\documentclass[10pt]{article}

\usepackage{fullpage}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{titlesec}
\usepackage[section]{placeins}
\usepackage{xcolor}
\usepackage{breakcites}
\usepackage{lineno}
\usepackage{hyphenat}





\PassOptionsToPackage{hyphens}{url}
\usepackage[colorlinks = true,
            linkcolor = blue,
            urlcolor  = blue,
            citecolor = blue,
            anchorcolor = blue]{hyperref}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother


\usepackage{natbib}




\renewenvironment{abstract}
  {{\bfseries\noindent{\abstractname}\par\nobreak}\footnotesize}
  {\bigskip}

\titlespacing{\section}{0pt}{*3}{*1}
\titlespacing{\subsection}{0pt}{*2}{*0.5}
\titlespacing{\subsubsection}{0pt}{*1.5}{0pt}


\usepackage{authblk}


\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\providecommand{\tightlist}{\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}%

\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[greek,ngerman,english]{babel}



\usepackage{float}








\begin{document}

\title{Low-energy driven ring-opening behavior of benzocyclobutene derivatives}



\author[1]{Ziwei Yuan}%
\author[1]{Quan Sun}%
\author[2]{Jinchong Xiao}%
\author[1]{Pingxia Zhang}%
\author[3]{Konstantin Levchenko}%
\author[3]{Dmitry Demin}%
\author[1]{Wenxin Fu}%
\affil[1]{Institute of Chemistry Chinese Academy of Sciences}%
\affil[2]{Hebei University}%
\affil[3]{MIREA Russian Technological University}%


\vspace{-1em}



  
  \date{May 26, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
It's urgent to develop benzocyclobutene (BCB)-based polymers with low
curing temperatures for temperature-sensitive applications such as
liquid crystal display (LCD) and flexible electronics. Herein, the
effect of substituents on the ring-opening behavior of BCB derivatives
was investigated. The ring-opening activation energy barriers (\selectlanguage{greek}Δ\selectlanguage{english}GA) of
BCB derivatives with one or two substituents on the four-membered alkyl
ring were systematically calculated using the B3LYP function. Both mono-
and di-substituted BCBs adopted the conrotatory ring-opening process,
obeying the Woodward-Hoffmann's Rules upon heating. The
mono-/di-substituted BCBs ex-hibited 8.2 -- 69\% lower \selectlanguage{greek}Δ\selectlanguage{english}GA compared with
BCB, attributed to the electronic effects of the substituents.
Disubstituted BCBs with both electron-donating and electron-withdrawing
groups, e.g., 1-NH2-8-NO2-BCB, demonstrated the lowest \selectlanguage{greek}Δ\selectlanguage{english}GA. In addition,
BCB derivatives with amide/ester/acyloxy group modified on C1 position
were synthesized as model molecules, and their ring-opening temperature
can be decreased by 20 \selectlanguage{ngerman}°C compared to the unsubstituted one, also
consistent with our calculation results. This work combined the
theoretical calculation method with experimental results to provide
valuable insights into the design and synthesis of BCB derivatives and
next-generation BCB functional packaging materials with low ring-opening
temperatures.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy


\textbf{Cite this paper:}\emph{Chin. J. Chem.} \textbf{2023} , \emph{41}
, XXX---XXX. \textbf{DOI: 10.1002/cjoc.202300XXX}

Low-energy driven ring-opening behavior of benzocyclobutene derivatives

Ziwei Yuan,\textsuperscript{a,c} Quan Sun,\textsuperscript{a,b} Jinchong
Xiao,*\textsuperscript{,\emph{c}} Pingxia
Zhang,*\textsuperscript{,a}Konstantin S. Levchenko,\textsuperscript{d}
Dmitry Y. Demin,\textsuperscript{d} and Wenxin Fu*\textsuperscript{,a,b}

\textsuperscript{a} Laboratory of Science and Technology on High-Tech
Polymer Materials, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, China\textsuperscript{b} University of Chinese Academy
of Sciences, Beijing 100049, China\textsuperscript{c} College of
Chemistry and Material Science, Hebei University, Baoding 071002,
China\textsuperscript{d} MIREA --- Russian Technological University,
Moscow 119454, Russian Federation\selectlanguage{english}
\begin{longtable}[]{@{}l@{}}
\toprule
\textbf{Keywords}\tabularnewline
\midrule
\endhead
Benzocyclobutene \textbar{} Low curing temperature \textbar{} Activation
energy barrier \textbar{} Electronic effect \textbar{} Captodative
effect\tabularnewline
\textbf{Comprehensive Summary}\tabularnewline
. It's urgent to develop benzocyclobutene (BCB)-based polymers with low
curing temperatures for temperature-sensitive applications such as
liquid crystal display (LCD) and flexible electronics. Herein, the
effect of substituents on the ring-opening behavior of BCB derivatives
was investigated. The ring-opening activation energy barriers
(\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}) of BCB derivatives with one or two substituents on
the four-membered alkyl ring were systematically calculated using the
B3LYP function. Both mono- and di-substituted BCBs adopted the
conrotatory ring-opening process, obeying the Woodward-Hoffmann's Rules
upon heating. The mono-/di-substituted BCBs exhibited 8.2 -- 69\% lower
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} compared with BCB, attributed to the electronic
effects of the substituents. Disubstituted BCBs with both
electron-donating and electron-withdrawing groups, e.g.,
1-NH\textsubscript{2}-8-NO\textsubscript{2}-BCB, demonstrated the lowest
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}. In addition, BCB derivatives with
amide/ester/acyloxy group modified on C\textsubscript{1} position were
synthesized as model molecules, and their ring-opening temperature can
be decreased by 20 \selectlanguage{ngerman}°C compared to the unsubstituted one, also consistent
with our calculation results. This work combined the theoretical
calculation method with experimental results to provide valuable
insights into the design and synthesis of BCB derivatives and
next-generation BCB functional packaging materials with low ring-opening
temperatures.\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{ngerman}

\section*{}

{\label{section}}

Background and Originality Content

Electrocyclic reaction as one of the widely used synthetic methods in
organic chemistry,\textsuperscript{1} exhibits excellent regio- and
stereo-control in construction of polycyclic scaffolds like
cyclopentanes, lactones, and cyclohexanones. The different ring-opening
stereochemical pathways are commonly described in terms of conrotatory
and disrotatory. In 1950s, The Frontier Molecular Orbital Theory
(FMO)\textsuperscript{2} proposed by Fukui successfully explained the
reactivity and regioselectivity phenomena of electrocyclic reaction.
Later, in 1969, Woodward and Hoffmann summarized the rule of
stereoselectivity for pericyclic reactions by the principle of symmetry
conservation of molecular orbitals.\textsuperscript{3} The
thermal-induced ring-opening of cyclobutene is a typical case of
electrocyclic reaction,\textsuperscript{4} and numerous studies have
investigated the effect of substituents on the ring-opening energy
barrier of cyclobutene and the torquoselectivity during the ring-opening
process.\textsuperscript{5} However, as a member of strained
four-membered cyclic ring family, benzocyclobutene (BCB) with
4\selectlanguage{greek}π-\selectlanguage{english}electron system stabilizing the cyclobutene ring can also undergo the
ring-opening reaction under heating conditions, but has received little
attention.\textsuperscript{6}

The thermal-induced ring-opening process of BCB\textsuperscript{7} also
follows the stereoselective rule of the electrocyclic reaction.
Moreover, the ring-opening reaction proceeds via a conrotatory pathway
to yield the unstable diene \emph{o} -quinodimethane (Scheme 1), due to
the loss of aromaticity after ring-opening.\textsuperscript{5e, 8}During
the ring-opening process, the C\textsubscript{1}-C\textsubscript{8} \selectlanguage{greek}σ
\selectlanguage{english}bond and the C\textsubscript{2}-C\textsubscript{7} \selectlanguage{greek}π \selectlanguage{english}bond are cleaved,
and two new \selectlanguage{greek}π \selectlanguage{english}bonds are formed: C\textsubscript{1}-C\textsubscript{2}
and C\textsubscript{7}-C\textsubscript{8}. Resins containing multiple
BCB functional groups are thermosetting materials, derived from
Diels--Alder (D-A) reaction by exploiting the high reactivity of\emph{o}
-quinodimethane.\textsuperscript{9} After fully cured, BCB resins
demonstrated high thermal stability, excellent mechanical and
low-dielectric properties,\textsuperscript{10} and have been widely used
as an advanced packaging material for the microelectronic
industry.\textsuperscript{11}

BCB resins have been reported as an organic passivation layer and
packaging material in liquid crystal displays (LCDs), owing to its
moderate curing temperature ([?] 250 \selectlanguage{ngerman}°C).\textsuperscript{11a, 12} As LCDs
keep developing towards multifunctional and flexible wearable devices,
the flexible substrate cannot withstand the high curing temperature,
which may damage the internal components of electronic products, thereby
limiting the further applications of BCB resins. It was found that
modifying the phenyl ring of BCB derivatives had no significant effect
on reducing its ring-opening temperature (peak temperature of DSC
curves), whereas modifications on the four-membered alkyl ring could
substantially influence the ring-opening activation
energy.\textsuperscript{11d, 13} Chino et al. synthesized four BCB
derivatives with electron-donating groups (methoxy, hydroxyl, acetoxyl,
(trimethylsilyl)oxyl groups on C\textsubscript{1}) and three ones with
electron-withdrawing groups (cyano-, chloro-, bromo-groups on
C\textsubscript{1}). All of them demonstrated low ring-opening
temperatures (\textless{} 200 °C).\textsuperscript{14} Dobish et al.
reported a polyacrylate modified with 1-alkoxy substituted BCB as the
pendant side chains, successfully reducing the cross-linking temperature
by 100 °C for the formation of intra-molecular
nanoparticles.\textsuperscript{11e} Hayes et al. synthesized
1-alkoxyl/hydroxyl/carbonyl group substituted BCB derivatives,
exhibiting ring-opening temperatures as low as 148 - 231 °C, and
believed that there might be an electronic relationship between the
structure of BCB ring and the temperature at which electrocyclic ring
opening occured.\textsuperscript{11d}

As early as 1978, Roth et al. experimentally linked the thermal
ring-opening reaction of BCB to D-A reaction to obtain a ring-opening
activation energy barrier (\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}) of 39.9 kcal/mol for
BCB.\textsuperscript{15} Chino et al. characterized the
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} as the enthalpy change, and utilized semi-empirical
molecular orbital calculations to determine the barrier, as well as
predicted the ring-opening temperatures of monosubstituted BCBs at
C\textsubscript{1}-position.\textsuperscript{16} Nava et al. analyzed
the effects of three factors on the stability of the closed and open
ring forms of cyclobutene and BCB: hyperconjugation, \selectlanguage{greek}π-\selectlanguage{english}delocalization
and ring strain.\textsuperscript{5e} Even so, the stereoelectronic
effect of substituents on the four-membered ring should be the interior
cause to influence the stability of BCB.\textsuperscript{17} To the best
of our knowledge, how substituents influence the ring-opening behavior
of BCBs has not been systematically studied yet. In this work, density
functional theory (DFT) calculations were employed to reveal the effects
of different types (electron-withdrawing/donating groups) and numbers
(one or two) of substituents on C\textsubscript{1} and
C\textsubscript{8} position of BCBs on their corresponding ring-opening
tendencies. Furthermore, a series of BCB model compounds with
amide/ester/acyloxy modifications on C\textsubscript{1} position were
synthesized, to validate the theoretical calculation results (Scheme 1).
Our findings provide a theoretical support for the research and
development of novel low-temperature curable BCB resins, and expand its
potential applications on flexible electronics,\textsuperscript{13,
18}interfacial bonding materials,\textsuperscript{19} etc.

\textbf{Scheme 1} a) Scheme of ring-opening reaction of BCB and its
possible energy changes. b) Design of the mono-/di-substituted BCB
derivatives.

Results and Discussion

Mechanism of thermal-induced ring-opening of BCB derivatives

The thermal-induced ring-opening process of BCB to\emph{o}
-quinodimethane generally follows the principle of molecular orbital
symmetry.\textsuperscript{3} According to the stereoselectivity rule of
the electrocyclization reaction, \emph{o} -quinodimethane owns eight
\selectlanguage{greek}π-\selectlanguage{english}electrons, and BCB adopts the conrotatory ring-opening pathway under
heating condition. In 2000, Sakai employed \emph{ab initio}molecular
orbital methods to investigate the transition state of the reaction
(\emph{o} -quinodimethane to BCB) on both conrotatory and disrotatory
paths, revealing a minimal difference in activation energy between them
(less than 8 kcal/mol).\textsuperscript{20} The planarity of the BCB
system significantly influences the ring-opening mechanism. Due to the
partial connection of the alkyl ring to a rigid benzene ring, the system
possesses a high degree of planarity that favors alkyl ring-opening
through a conrotatory pathway. Lee et al. have confirmed that as the
planarity of a system increases, conrotatory ring-opening becomes more
favorable.\textsuperscript{5c}

The elucidation of ring-opening pathways for substituted BCB derivatives
is crucial. Upon introducing a substituent to the alkyl ring of BCB, two
torsional pathways can be taken: inward and outward. The specific
pathway is determined by the electronic effect between the
\emph{p}orbital of the substituent and the orbital of the broken \selectlanguage{greek}σ \selectlanguage{english}bond
(C\textsubscript{1}-C\textsubscript{8} bond) at the transition state. By
conducting calculations (Figure 1), it was determined that the \selectlanguage{greek}σ-\selectlanguage{english}bond
(C\textsubscript{1}-C\textsubscript{8}) was broken at the highest
occupied molecular orbital (HOMO) of transition state, with the lowest
unoccupied molecular orbital (LUMO) of the \selectlanguage{greek}σ\selectlanguage{english}* orbital. In case of an
electron-donating group, such as NH\textsubscript{2}, presented as a
substituent at C\textsubscript{1} position, the HOMO orbital experienced
strong repulsion due to the filled \emph{p} orbital of the substituent
interacting with the orbital of the broken \selectlanguage{greek}σ \selectlanguage{english}bond during inward pathway.
For LUMO orbitals, rotation of the substituent inward results in the
formation of a node-like structure between the \emph{p} orbital of the
substituent and the orbital of the broken bond, causing the transition
state to become unstable.

However, this pathway cannot be applied to electron-withdrawing groups.
In 1992, Jefford et al. experimentally and theoretically explored the
torquoselectivity of ring opening of 1-substituted BCBs, such as
1-CN-BCB and 1-COOH-BCB, utilizing D-A reaction of BCB derivatives with
maleic anhydride, and inferred the \emph{o} -quinodimethane conformation
accordingly. It was found that 1-CN-BCB, 1-COOH-BCB and 1-COOMe-BCB were
ring-opened outwards, whereas the 1-formyl substituted one turned
inwards.\textsuperscript{7} Therefore, further investigation was
required to understand the reasons behind the torquoselectivity of
ring-opening for different substituents. In order to shed light on this
matter, nine different substituents with different electronic effects
were selected to verify the ring-opening pathway. Through DFT
calculations, the conrotatory pathway can be determined.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\textbf{Figure 1} HOMO and LUMO orbitals of the transition states of
1-NH\textsubscript{2}-BCB and 1-NO\textsubscript{2}-BCB.

Ring-opening of C\textsubscript{1}-position monosubstituted BCB
derivatives

Previous experimental and theoretical studies found that a high
activation energy barrier was required in the thermal-induced
ring-opening of BCB due to the loss of aromaticity.\textsuperscript{5e,
15, 17} Meanwhile, the ring-opening temperature of BCB derivatives
should be associated with the ring-opening activation energy barrier
(\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}). The higher \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} corresponded to
the higher ring-opening temperature, and vice versa. Four
electron-donating groups (NH\textsubscript{2}, OH,
OCOCH\textsubscript{3}, CH\textsubscript{3}), three electron-withdrawing
groups (NO\textsubscript{2}, CN, COOH), and two halogen substituents
(Br, F) were selected to study the effect of substituents at the
C\textsubscript{1} position on \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}. The ring-opening
temperatures of 1-Br-BCB,1-OH-BCB,1-COOH-BCB were defined by
differential scanning calorimetry (DSC) (Table S1, Figure S1). Among
them, the ring-opening temperature of 1-COOH-BCB was basically
consistent with the reported one. Whereas, the ring-opening temperature
of 1-OH-BCB, presenting at 156 \selectlanguage{ngerman}°C, was much higher than the previous
report of 80 °C.\textsuperscript{17} Besides, according to Chino's
report,\textsuperscript{16} 1-Br-BCB demonstrated an endothermic peak,
not matched with the regular exothermic effect of ring-opening reaction
and D-A reaction. But 1-Br-BCB based on our synthetic procedure
exhibited an exothermic peak with ring-opening temperature of 150 °C.
The \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of unsubstituted BCB was obtained as 37.20
kcal/mol at B3LYP/6-311G(d,p) with dispersion correction introduced,
which was consistent with the experimental value (40
kcal/mol).\textsuperscript{5c, 15} A positive correlation between
temperature and energy barrier was determined (Table S1). Extensive
calculations were performed at this level, and the results were shown in
Figure 2a and 2b.

The substituents on the alkyl ring can effectively reduce
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}, and \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} is related to the
electronic activities of the substituents. The introduction of the
strong electron-donating NH\textsubscript{2} group at
C\textsubscript{1}position (1-NH\textsubscript{2}-BCB), resulted in the
lowest \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} value, which was 13.13 kcal/mol (35.3\%)
lower than that of unsubstituted BCB. The \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of
1-OH-BCB and 1-OCOCH\textsubscript{3}-BCB were 27.59 and 31.82 kcal/mol,
which were 9.61 and 5.38 kcal/mol (25.8\%, 14.5\%) lower than that of
unsubstituted BCB, respectively. A clear correlation can be observed
between the electron-donating abilities of substituents and the
corresponding \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} values: substituents with higher
electron-donating ability exhibited lower \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} values,
which was consistent with the substituent effect of thermal ring-opening
of cyclobutene.\textsuperscript{5a} Furthermore, a strong linear
relationship existed between the electron-donating ability of the
substituents and the corresponding \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} values.

Different from the electron-donating effect, although the introduction
of electron-withdrawing group at the C\textsubscript{1} position of BCB
can also result in a decrease of \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}, no direct
relationship was found between the electron-withdrawing ability of the
substituents and \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} values. Compared with 1-COOH-BCB
(with \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of 34.15 kcal/mol) and
1-NO\textsubscript{2}-BCB (with \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of 33.4 kcal/mol),
1-CN-BCB decreased \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} to 31.08 kcal/mol, 6.12 kcal/mol
(16.5\%) lower than the unsubstituted BCB. As for the two halogen
substituents, 1-Br-BCB was about 33.59 kcal/mol, and comparatively the
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of 1-F-BCB was 0.36 kcal/mol lower than that of
1-Br-BCB, owing to its stronger electron-withdrawing ability.

The Gibbs free energy change (\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{R}) of the ring-opening
reaction can actually evaluate the stabilities of initial (cyclic ring)
and final (conjugated diene) state. From 1-NH\textsubscript{2}-BCB to
1-CH\textsubscript{3}-BCB, as the electron-donating ability decreased,
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{R} gradually increased from 1.46 to 8.94 kcal/mol. On
the other hand, for electron-withdrawing groups, the
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{R}increased from 3.01, 4.23 to 9.85 kcal/mol with
increasing electron-withdrawing abilities from 1-COOH-BCB, 1-CN-BCB to
1-NO\textsubscript{2}-BCB. Besides, the \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{R} of the two
halogen-substituted BCBs (1-F-BCB and 1-Br-BCB) were higher than that of
unsubstituted BCB (9.63 kcal/mol). Based on the above calculation
results, the stronger electron-donating or weaker electron-withdrawing
ability the substituent group owned, the more stable the ring-opened
diene intermediate was.

Ring-opening of C\textsubscript{1} and C\textsubscript{8}-position
disubstituted BCB derivatives

To further understand the electronic effect on the ring-opening of BCB,
eight substituents with different electronic effects, including
NH\textsubscript{2}, OH, OCOCH\textsubscript{3}, CH\textsubscript{3} as
electron-donating groups, and NO\textsubscript{2}, CN, Br, COOH as
electron-withdrawing groups, were selected to modify the
C\textsubscript{1} and C\textsubscript{8} positions of BCB. All possible
arrangements of substituents were considered. The results were shown in
Figure 2c and 2d. Interestingly, four distinct conclusions can be drawn
regarding the relationship between the \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of these
disubstituted BCBs and its corresponding substituent effects.

(1) The \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of the disubstituted BCB was lower than that
of the corresponding monosubstituted BCB. Specifically, when
R\textsubscript{1} was fixed as NH\textsubscript{2} and
R\textsubscript{2} varied from NH\textsubscript{2} to
NO\textsubscript{2} (named as
1-NH\textsubscript{2}-8-R\textsubscript{2}-BCB),
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}decreased from 21.49 kcal/mol to 11.54 kcal/mol, less
than that of 1-NH\textsubscript{2}-BCB (24.06 kcal/mol). A similar trend
was observed when R\textsubscript{1} was fixed as OH and other groups.
(Figure 2c).

(2) The \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of the disubstituted BCB with an
electron-donating group was lower than that with electron-withdrawing
groups. In the diagonal position in Figure 2c (R\textsubscript{1} =
R\textsubscript{2}), from
1-NH\textsubscript{2}-8-NH\textsubscript{2}-BCB to
1-NO\textsubscript{2}-8-NO\textsubscript{2}-BCB, as the
electron-withdrawing ability of R\textsubscript{1} and
R\textsubscript{2} increased simultaneously,
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}increased. From
1-NO\textsubscript{2}-8-NH\textsubscript{2}-BCB to
1-NO\textsubscript{2}-8-NO\textsubscript{2}-BCB, where
R\textsubscript{1} was fixed as NO\textsubscript{2}, as the
electron-withdrawing ability of R\textsubscript{2} increased,
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} increased gradually. Similar trends were observed
when R\textsubscript{2} was fixed as other electron-withdrawing groups.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

\textbf{Figure 2} a) Calculated \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} and b)
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{R} of C\textsubscript{1}-position monosubstituted BCB
derivatives. c) Calculated \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} and d)
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{AC} of disubstituted BCB derivatives.

Furthermore, when R\textsubscript{1} changed from CH\textsubscript{3} to
NH\textsubscript{2} and R\textsubscript{2} was fixed as
NH\textsubscript{2} (i.e.,
1-CH\textsubscript{3}-8-NH\textsubscript{2}-BCB to
1-NH\textsubscript{2}-8-NH\textsubscript{2}-BCB), the
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of disubstituted BCB decreased from 21.49 to 16.55
kcal/mol, indicating a decrease in \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} with increasing
electron-donating ability of substituents.

(3) An extra reduction of \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} was observed, known as the
``captodative effect'',\textsuperscript{5a} when R\textsubscript{1} was
an electron-donating group (NH\textsubscript{2}, OH,
OCOCH\textsubscript{3}, CH\textsubscript{3}) and R\textsubscript{2} was
an electron-withdrawing group (NO\textsubscript{2}, CN and COOH).

``Captodative effect'' (\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{AC}): \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{AC} =
{[}\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A of BCB} - \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A of 1-R1-8-R2-BCB}{]}
- {[}\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A of BCB} - \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A of 1-R1-BCB}{]} -
{[}\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A of BCB} - \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A of 1-R2-BCB}{]}. For
example, \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{AC} of
1-NH\textsubscript{2}-8-NO\textsubscript{2}-BCB = (37.2 -11.54) - (37.2
-24.07) - (37.2 -33.4) = 8.73 kcal/mol.

All BCB molecules with ''captodative effect'' were listed in Figure 2d.
Among them, \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{AC} of
1-NH\textsubscript{2}-8-NO\textsubscript{2}-BCB was the largest. The
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{AC} of 1-NH\textsubscript{2}-8-R\textsubscript{2}-BCB
was larger than that of 1-OH-8-R\textsubscript{2}-BCB,
1-OCOCH\textsubscript{3}-8-R\textsubscript{2}-BCB and
1-CH\textsubscript{3}-8-R\textsubscript{2}-BCB, respectively. The
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{AC} increased with the electron-donating ability of
R\textsubscript{1}.

(4) In addition to the calculation of \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}, the
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{R} for the ring-opening reaction of disubstituted BCBs
were also determined (Figure S2). For a fixed R\textsubscript{1} and
varying R\textsubscript{2} as electron-donating groups
(NH\textsubscript{2}, OH, OCOCH\textsubscript{3}, CH\textsubscript{3}),
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{R} decreased gradually with the increase in the
electron-donating ability, similar to the trend observed for
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}. Intriguingly, when R\textsubscript{1} =
NH\textsubscript{2} and R\textsubscript{2} changed from
NH\textsubscript{2}, COOH, CN to NO\textsubscript{2}, the
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{R} of the four compounds were less than zero. Moreover,
the \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of these four BCBs were the lowest among all the
disubstituted BCBs, with values of 16.55, 13.46, 11.82, and 11.54
kcal/mol, respectively. This indicated that the ring-opening of these
four disubstituted BCBs may spontaneously proceed towards\emph{o}
-dimethylquinone at 25 \selectlanguage{ngerman}°C.

Ring-opening of monosubstituted BCB with complex electronic effect at
C\textsubscript{1}-position

For practical applications in microelectronic packaging, the
low-temperature cured BCB units are still required to be chemically
modified into a polymerizable monomer. Therefore, the simple
electron-donating/withdrawing groups at C\textsubscript{1} position may
further undergo coupling reactions to yield intricate pendant bonds,
demonstrating complex electronic and steric effects, such as ester,
amide, ether, etc., which could have a substantial impact on the
corresponding \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}.

\textbf{Scheme 2} Synthetic routes of compounds\textbf{3}
\textasciitilde{}\textbf{8} .

To investigate the \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of monosubstituted BCBs with
complex electronic effect at C\textsubscript{1} position and varying
spatial structures, we designed eight BCB molecules and six of them
(compounds \textbf{3} \textasciitilde{} \textbf{8} ) were synthesized
(Scheme 2). The ring-opening temperatures of compounds
\textbf{3}\textasciitilde{} \textbf{8} were further determined by DSC to
verify their corresponding \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} and the results were
shown in Figure 3.

The DSC curves for compounds \textbf{3}
\textasciitilde{}\textbf{8}showed very similar ring-opening temperatures
at around 230 \selectlanguage{ngerman}°C, which was only about 20 °C lower than that of pristine
BCB (Figure 3b). Consistently, their calculated \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} were
also distributed around 31 kcal/mol, slightly lower than that of BCB
(6.2 kcal/mol, 16.7\%, Figure 3a). Notably, compounds \textbf{1} and
\textbf{2}exhibited lower \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} values of 25.42 and 27.13
kcal/mol, respectively, which were significantly lower than those of
compounds\textbf{3} \textasciitilde{}\textbf{8} . This effect can be
attributed to the strong electron-donating effect of the
NH\textsubscript{2} group. Based on the DFT calculations and DSC
results, we found that modification on simple groups such as
NH\textsubscript{2}, OH COOH, could greatly change the electronic
effect. And spatial structure of different substituents had little
effect on the \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} and ring-opening temperatures of BCBs,
consistent with Willson et al.'s report.\textsuperscript{11d}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image8/image8}

\end{center}
\end{figure}

\textbf{Figure 3} a) The calculated \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of
compounds\textbf{1} \textasciitilde{}\textbf{8} . b) DSC curves of
compounds\textbf{3} \textasciitilde{}\textbf{8.}

Conclusions

A systematic study of the substituent effect on the ring-opening
behavior of BCB derivatives has been presented. The principal findings
were as follows: the mono-/di-substituted BCBs, no matter with
electron-donating groups or electron-withdrawing groups, demonstrated
8.2 -- 69\% lower \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} than the unsubstituted one. The
stronger electron-donating ability the substituents owned, the lower
\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} values it exhibited (e.g.,
1-NH\textsubscript{2}-BCB). The disubstituted BCBs with both an
electron-donating group and an electron-withdrawing group at
C\textsubscript{1}- and C\textsubscript{8}-position, respectively,
exhibited the lowest \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A} of 11.54 kcal/mol, possibly due
to the captodative effect between two substituents with distinct
electronic attributes. Moreover, complex pendant chemical bonds, such as
amide (CONHR), ester (COOR), acyloxy (OCOR), can substantially modify
its electronic effect and \selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}. These complex pendant
substituents can reduce the ring-opening temperature by 20 \selectlanguage{ngerman}°C compared
to unsubstituted BCB, similar to the effects of electron-withdrawing
groups. These results offer a theoretical basis for developing BCB-based
functional materials with low curing temperatures and further promote
the expansion of BCB application fields in high-temperature sensitive
fields such as advanced displays and flexible electronics.

Experimental

Compound \textbf{3} : 100mg 1-OH-BCB and 78mg propionic acid were added
in a 25mL round-bottomed flask, then 5mL dry DCM was injected. And 191mg
EDC and 122mg DMAP were added whereupon it was cooled. The mixture was
stirred overnight under a nitrogen atmosphere at room temperature. After
the reaction was completed, the solution was washed with 0.1mol/L HCl
solution (60mL) and DCM (20 mL × 3). Repeat with saturated salt and DCM.
The organic layer was dried over MgSO\textsubscript{4} and evaporated in
vacuo. Compound 7 was obtained as a colorless liquid with a yield of
80.5\%. \textsuperscript{1}H NMR (300 MHz, Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}7.32
(dq, \emph{J} = 8.3, 4.2 Hz, 1H), 7.24 (s, 1H), 7.15 (d, \emph{J} = 7.2
Hz, 1H), 5.93 (d, \emph{J} = 4.7 Hz, 1H), 3.67 (dd, \emph{J} = 14.5, 4.6
Hz, 1H), 3.22 (d, \emph{J} = 14.6 Hz, 1H), 2.39 (q, \emph{J} = 7.6 Hz,
2H), 1.18 (t, \emph{J} = 7.6 Hz, 3H). \textsuperscript{13}C NMR (75 MHz,
Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}174.50, 144.35, 142.76, 129.94, 127.51, 123.57,
123.20, 77.25, 71.48, 38.95, 27.52, 9.06.

Compound \textbf{4} : 100 mg 1-OH-BCB, 175 mg benzoyl chloride were
added in a 25 mL round-bottomed flask. Then 5mL dry DCM was injected,
cooled in an ice bath for 5 min, 168 mg Et\textsubscript{3}N was added,
and stirred at room temperature overnight. After the reaction was
completed, the reaction solution was washed with saturated salt
water(60mL) and DCM (20mL \selectlanguage{ngerman}× 3). The organic layer was dried over
MgSO\textsubscript{4} and evaporated in vacuo. Compound 8 was obtained
as light yellow liquid with a yield of 81.7\%. \textsuperscript{1}H NMR
(400 MHz, Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}8.12 -- 8.06 (m, 2H), 7.56 (t,
\emph{J}= 7.4 Hz, 1H), 7.44 (t, \emph{J} = 7.8 Hz, 2H), 7.38 -- 7.32 (m,
2H), 7.29 (d, \emph{J} = 8.4 Hz, 1H), 7.19 (d, \emph{J} = 7.2 Hz, 1H),
6.18 (dd, \emph{J} = 4.6, 2.0 Hz, 1H), 3.78 (dd, \emph{J} = 14.5, 4.5
Hz, 1H), 3.39 (d, \emph{J} = 13.7 Hz, 1H). \textsuperscript{13}C NMR (75
MHz, Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}166.58, 144.31, 142.80, 133.04, 130.06,
129.72, 128.35, 127.58, 123.73, 123.25, 77.24, 72.02, 39.09.

Compound \textbf{5} : 300 mg 1-COOH-BCB and 8mL sulfoxide chloride were
added in a 25 mL round-bottomed flask. The mixture was refluxed at 80\selectlanguage{ngerman}°C
for 3 h until no bubbles were generated. The excess sulfoxide chloride
was evaporated in vacuo, then it was diluted by 2mL dry DCM. 219mg
n-butylamine, 310 mg triethylamine and 2 mL dry DCM were added to
another flask. And acyl chloride, diluted by 2mL dry DCM, was dropwised
under ice bath. The reaction solution was stirred at room temperature
overnight. After the reaction was finished, the reaction solution was
washed with saturated salt water(60mL) and DCM (20mL × 3). The organic
layer was dried over MgSO\textsubscript{4} and evaporated in vacuo. A
light yellow solid was obtained with a yield of 94\%.
\textsuperscript{1}H NMR (300 MHz, DMSO-\emph{d\textsubscript{6}} ) \selectlanguage{greek}δ
\selectlanguage{english}7.98 (d, \emph{J} = 5.9 Hz, 1H), 7.24 -- 7.15 (m, 2H), 7.13 -- 7.07 (m,
2H), 4.16 (t, \emph{J} = 3.9 Hz, 1H), 3.08 (qd, \emph{J} = 6.7, 3.8 Hz,
2H), 1.46 -- 1.20 (m, 5H), 0.87 (t,\emph{J} = 7.2 Hz, 3H).
\textsuperscript{13}C NMR (75 MHz, Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}171.88,
144.95, 142.81, 128.47, 127.68, 123.56, 122.17, 48.02, 39.28, 35.73,
31.66, 20.03, 13.75.

Compound \textbf{6} : 300mg 1-COOH-BCB and 226mg phenylamine were added
in a 25mL round-bottomed flask, then 10mL dry DCM was injected. And
389mg EDC and 248mg DMAP were added whereupon it was cooled. The mixture
was stirred overnight under a nitrogen atmosphere at room temperature.
After the reaction was completed, the solution was washed with 0.1mol/L
HCl solution (60mL) and DCM (20 mL \selectlanguage{ngerman}× 3). Repeat with saturated salt and
DCM. The organic layer was dried over MgSO\textsubscript{4} and
evaporated in vacuo. Compound 6 was obtained as a white solid with a
yield of 93\%. \textsuperscript{1}H NMR (400 MHz, DMSO-\emph{d}
\textsubscript{6}) \selectlanguage{greek}δ \selectlanguage{english}10.18 (s, 1H), 7.63 (d, \emph{J} = 8.0 Hz, 2H),
7.30 (t, \emph{J} = 7.7 Hz, 2H), 7.25 -- 7.17 (m, 3H), 7.14 (d,\emph{J}
= 6.0 Hz, 1H), 7.04 (t, \emph{J} = 7.4 Hz, 1H), 4.44 (dd,\emph{J} = 5.3,
2.8 Hz, 1H), 3.42 (dd, \emph{J} = 14.0, 2.8 Hz, 1H), 3.35 (dd, \emph{J}
= 14.0, 5.3 Hz, 1H). \textsuperscript{13}C NMR (75 MHz,
Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}170.19, 144.90, 142.30, 137.64, 129.01, 128.83,
127.94, 124.47, 123.73, 122.32, 119.89, 77.25, 48.83, 35.69.

Compound \textbf{7} : 200 mg of 1-COOH-BCB, 730 \selectlanguage{greek}µ\selectlanguage{english}L of MeOH were placed
in a schlenk tube. Then 333 \selectlanguage{greek}µ\selectlanguage{english}L of concentrated
H\textsubscript{2}SO\textsubscript{4} was added and refluxed overnight.
After the reaction was completed, the reaction solution was washed with
brine(60mL) and DCM (20mL \selectlanguage{ngerman}× 3). The organic layer was dried over
MgSO\textsubscript{4} and evaporated in vacuo. Compound 8 was obtained
as colorless liquid with a yield of 66\%. \textsuperscript{1}H NMR (400
MHz, Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}7.25 -- 7.21 (m, 2H), 7.17 (d, \emph{J} =
5.9 Hz, 1H), 7.10 (t, \emph{J} = 4.3 Hz, 1H), 4.32 (t, \emph{J} = 4.2
Hz, 1H), 3.74 (s, 3H), 3.50 -- 3.46 (m, 2H). \textsuperscript{13}C NMR
(75 MHz, Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}172.71, 144.22, 142.74, 128.21, 127.36,
122.92, 122.55, 77.24, 52.04, 45.79, 34.05.

Compound \textbf{8} : 200 mg 1-COOH-BCB and 5mL sulfoxide chloride were
added in a 25 mL round-bottomed flask. The mixture was refluxed at 80\selectlanguage{ngerman}°C
for 3 h until no bubbles were generated. The excess sulfoxide chloride
was evaporated in vacuo, then it was diluted by 2mL dry DCM. 188 mg
phenol, 280 mg triethylamine and 3 mL dry DCM were added to another
flask. And acyl chloride, diluted by 2mL dry DCM, was dropwised under
ice bath. The reaction solution was stirred at room temperature
overnight. After the reaction was finished, the reaction solution was
washed with brine(60mL) and DCM (20mL × 3). The organic layer was dried
over MgSO\textsubscript{4} and evaporated in vacuo. A colorless liquid
was obtained with a yield of 71\%. \textsuperscript{1}H NMR (300 MHz,
Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}7.36 (t, \emph{J} = 7.7 Hz, 2H), 7.22
(d,\emph{J} = 6.8 Hz, 3H), 7.16 -- 7.04 (m, 3H), 4.54 (dd, \emph{J} =
5.4, 3.0 Hz, 1H), 3.58 (qd, \emph{J} = 14.3, 4.2 Hz,
2H).\textsuperscript{13}C NMR (75 MHz, Chloroform-\emph{d} ) \selectlanguage{greek}δ \selectlanguage{english}170.69,
150.81, 144.22, 142.40, 129.66, 129.43, 128.47, 127.57, 125.87, 123.08,
122.60, 121.51, 115.27, 77.24, 46.05, 34.02.

Supporting Information

The supporting information for this article is available on the WWW
under https://doi.org/10.1002/cjoc.2023xxxxx.

Acknowledgement

This work was supported by the National Natural Science Foundation of
China (No. 22075298, 2022000168) and Beijing Municipal Natural Science
Foundation (No. 2212053).

References

\begin{enumerate}
\tightlist
\item
  (a)Ding, H.; Bian, M.; Li, L., Recent Advances on the Application of
  Electrocyclic Reactions in Complex Natural Product
  Synthesis.\emph{Synthesis} \textbf{2017,} \emph{28} , 4383-4413;
  (b)Cai, Y.; Tang, Y.; Atodiresei, I.; Rueping, M., Catalytic
  Asymmetric Piancatelli Rearrangement: Bronsted Acid Catalyzed 4pi
  Electrocyclization for the Synthesis of Multisubstituted
  Cyclopentenones. \emph{Angew. Chem. Int. Ed.} \textbf{2016,}\emph{55}
  , 14126-14130; (c)Dolbier, W. R.; Koroniak, H.; Houk, K. N.; Sheu, C.
  M., Electronic control of stereoselectivities of electrocyclic
  reactions of cyclobutenes: A triumph of theory in the prediction of
  organic reactions. \emph{Acc. Chem. Res.} \textbf{1996,}\emph{29} ,
  471-477; (d)Houk, K. N.; Li, Y.; Evanseck, J. D., Transition
  Structures of Hydrocarbon Pericyclic-Reactions.\emph{Angew. Chem. Int.
  Ed.} \textbf{1992,} \emph{31} , 682-708; (e)Woodward, R. B.; Hoffmann,
  R., Stereochemistry of Electrocyclic Reactions. \emph{J. Am. Chem.
  Soc.} \textbf{1965,} \emph{87} , 395-397.
\item
  Houk, K. N., Fontier molecular-orbital theory of cycloaddition
  reactions. \emph{Acc. Chem. Res.} \textbf{1975,} \emph{8} , 361-369.
\item
  (a)Hoffmann, R.; Woodward, R. B., Orbital symmetry control of chemical
  reactions. \emph{Science} \textbf{1970,} \emph{167} , 825-831;
  (b)Woodward, R. B.; Hoffmann, R., Conservation of Orbital
  Symmetry.\emph{Angew. Chem. Int. Ed.} \textbf{1969,} \emph{8} ,
  781-853.
\item
  Sadana, A. K.; Saini, R. K.; Billups, W. E., Cyclobutarenes and
  related compounds. \emph{Chem. Rev.} \textbf{2003,} \emph{103} ,
  1539-1602.
\item
  (a)Sheikh, N. S., Captodative substitution induced acceleration effect
  towards 4\selectlanguage{greek}π \selectlanguage{english}electrocyclic ring-opening of substituted
  cyclobutenes.\emph{RSC Adv.} \textbf{2016,} \emph{6} , 25503-25510;
  (b)Lee, P. S.; Zhang, X. Y.; Houk, K. N., Origins of inward
  torquoselectivity by silyl groups and other sigma-acceptors in
  electrocyclic reactions of cyclobutenes. \emph{J. Am. Chem. Soc.}
  \textbf{2003,} \emph{125} , 5072-5079; (c)Lee, P. S.; Sakai, S.;
  Horstermann, P.; Roth, W. R.; Kallel, E. A.; Houk, K. N., Altering the
  allowed/forbidden gap in cyclobutene electrocyclic reactions:
  Experimental and theoretical evaluations of the effect of planarity
  constraints. \emph{J. Am. Chem. Soc.} \textbf{2003,} \emph{125} ,
  5839-5848; (d)Brown, C. L.; Bowser, B. H.; Meisner, J.; Kouznetsova,
  T. B.; Seritan, S.; Martinez, T. J.; Craig, S. L., Substituent Effects
  in Mechanochemical Allowed and Forbidden Cyclobutene Ring-Opening
  Reactions. \emph{J. Am. Chem. Soc.}\textbf{2021,} \emph{143} ,
  3846-3855; (e)Nava, P.; Carissan, Y., On the ring-opening of
  substituted cyclobutene to benzocyclobutene: analysis of pi
  delocalization, hyperconjugation, and ring strain.\emph{Phys. Chem.
  Chem. Phys.} \textbf{2014,} \emph{16} , 16196-203.
\item
  Kotha, S.; Lahiri, K.; Tangella, Y., Recent Advances in
  Benzocyclobutene Chemistry. \emph{Asian J. Org. Chem.}
  \textbf{2021,}\emph{10} , 3166-3185.
\item
  Jefford, C. W.; Bernardinelli, G.; Wang, Y.; Spellmeyer, D. C.; Buda,
  A.; Houk, K. N., Torquoselectivity in the Electrocyclic Conversion of
  Benzocyclobutenes to Ortho-Xylylenes. \emph{J. Am. Chem.
  Soc.}\textbf{1992,} \emph{114} , 1157-1165.
\item
  Segura, J. L.; Martin, N., o-Quinodimethanes: Efficient intermediates
  in organic synthesis. \emph{Chem. Rev.} \textbf{1999,} \emph{99} ,
  3199-3246.
\item
  (a)Levchenko, K. S.; Chudov, K. A.; Adamov, G. E.; Poroshin, N. O.;
  Shmelin, P. S.; Grebennikov, E. P.; Parshikov, Y. G., Photocurable and
  Thermosetting Polymer Materials on the Basis of Benzocyclobutene and
  Its Derivatives for Electronics. \emph{Russ. J. Gen.
  Chem.}\textbf{2019,} \emph{88} , 2793-2812; (b)Cao, K.; Yang, L.;
  Huang, Y.; Chang, G.; Yang, J., High temperature thermosets derived
  from benzocyclobutene-containing main-chain oligomeric
  carbosilanes.\emph{Polymer} \textbf{2014,} \emph{55} , 5680-5688.
\item
  (a)Chen, X.; Wang, J.; Sun, J.; Fang, Q., High performance low
  dielectric polysiloxanes with high thermostability and low water
  uptake. \emph{Mater. Chem. Front.} \textbf{2018,} \emph{2} ,
  1397-1402; (b)Li, M.; Sun, J.; Fang, Q., A fluoropolymer with a low
  dielectric constant at a high frequency derived from bio-based
  anethole.\emph{Polym. Chem.} \textbf{2021,} \emph{12} , 4501-4507;
  (c)Hou, J.; Sun, J.; Fang, Q., A fluorinated low dielectric polymer at
  high frequency derived from allylphenol and benzocyclobutene by a
  facile route. \emph{Eur. Polym. J.} \textbf{2022,} \emph{163} .
\item
  (a)Zuo, X.; Yu, R.; Shi, S.; Feng, Z.; Li, Z.; Yang, S.; Fan, L.,
  Synthesis and Characterization of Benzocyclobutene-Functionalized
  Photosensitive Siloxane Thermosets. \emph{J. Polym. Sci., Part A:
  Polym. Chem.} \textbf{2009,} \emph{47} , 6246-6258; (b)Zuo, X.; Zhao,
  X.; Liu, B.; Yang, S.; Fan, L., Synthesis and properties of
  fluorinated bis-benzocyclobutene-terminated arylene ether
  monomers.\emph{J. Appl. Polym. Sci.} \textbf{2009,} \emph{112} ,
  2781-2791; (c)Wu, S.; Peng, Q.; Deng, Y.; Shi, Q.; Ma, J.; Huang, Y.;
  Yang, J., Preparation and performance of low-dielectric
  benzocyclobutene resins containing dicyclopentadiene. \emph{J. Vinyl
  Addit. Technol.}\textbf{2022,} \emph{28} , 631-639; (d)Hayes, C. O.;
  Chen, P.-h.; Thedford, R. P.; Ellison, C. J.; Dong, G.; Willson, C.
  G., Effect of Ring Functionalization on the Reaction Temperature of
  Benzocyclobutene Thermoset Polymers. \emph{Macromolecules}
  \textbf{2016,} \emph{49} , 3706-3715; (e)Dobish, J. N.; Hamilton, S.
  K.; Harth, E., Synthesis of low-temperature benzocyclobutene
  cross-linker and utilization.\emph{Polym. Chem.} \textbf{2012,}
  \emph{3} , 857-860.
\item
  (a)Schuck, M. H.; McKnight, D. J.; Johnson, K. M., Spin-cast
  planarization of liquid-crystal-on-silicon microdisplays. \emph{Opt.
  Lett.} \textbf{1997,} \emph{22} , 1512-1514; (b)So, Y.-h.; Stark, E.
  J.; Li, Y.; Kisting, S.; Achen, A.; Baranek, K.; Scheck, D.; Hetzner,
  J.; Folkenroth, J. J.; Topper, M.; Baumgartner, T.,
  Aqueous-Base-Developable Benzocyclobutene (BCB)-Based Material Curable
  in Air. \emph{IEEE Trans. Adv. Packag.} \textbf{2006,} \emph{29} ,
  741-750.
\item
  Hallani, R. K.; Moser, M.; Bristow, H.; Jenart, M. V. C.; Faber, H.;
  Neophytou, M.; Yarali, E.; Paterson, A. F.; Anthopoulos, T. D.;
  McCulloch, I., Low-Temperature Cross-Linking Benzocyclobutene Based
  Polymer Dielectric for Organic Thin Film Transistors on Plastic
  Substrates. \emph{J. Org. Chem.} \textbf{2020,} \emph{85} , 277-283.
\item
  (a)Chino, K.; Takata, T.; Endo, T., Polymerization of
  o-quinodimethanes bearing electron-donating groups in situ formed by
  thermal isomerization of benzocyclobutenes.
  \emph{Macromolecules}\textbf{1997,} \emph{30} , 6715-6720; (b)Chino,
  K.; Takata, T.; Endo, T., Polymerization of o-quinodimethanes. III.
  Polymerization of o-quinodimethanes bearing electron-withdrawing
  groups formed in situ by thermal ring-opening isomerization of
  corresponding benzocyclobutenes. \emph{Polym. Chem.} \textbf{1999,}
  \emph{37} , 1555-1563.
\item
  Biermann, W. R. R. M., Das Energieprofil des
  o-Chinodimethan-Benzocyclobuten-Gleichgewichtes. \emph{Chem.
  Ber.}\textbf{1978,} \emph{111} , 3892-3903.
\item
  Chino, K.; Endo, T., Prediction of Thermal Isomerization Temperatures
  of Substituted Benzocyclobutenes to o-Quinodimethanes by
  Semi-Empirical Molecular Orbital Calculation. \emph{Lett. Org.
  Chem.}\textbf{2011,} \emph{8} , 138-142.
\item
  Balaban, A. T., Aromaticity and Conjugation in 1,2-Benzoquinone
  Valence Isomers and Congeners. In \emph{Adv. Heterocycl. Chem.} ,
  Elsevier, Vol. 113, \textbf{2014} , pp 111-142.
\item
  Motala, M. J.; Blanton, E. W.; Hilton, A.; Heller, E.; Muratore, C.;
  Burzynski, K.; Brown, J. L.; Chabak, K.; Durstock, M.; Snure, M.;
  Glavin, N. R., Transferrable AlGaN/GaN High-Electron Mobility
  Transistors to Arbitrary Substrates via a Two-Dimensional Boron
  Nitride Release Layer. \emph{ACS Appl Mater Interfaces}
  \textbf{2020,}\emph{12} , 21837-21844.
\item
  (a)Quellmalz, A.; Wang, X.; Sawallich, S.; Uzlu, B.; Otto, M.; Wagner,
  S.; Wang, Z.; Prechtl, M.; Hartwig, O.; Luo, S.; Duesberg, G. S.;
  Lemme, M. C.; Gylfason, K. B.; Roxhed, N.; Stemme, G.; Niklaus, F.,
  Large-area integration of two-dimensional materials and their
  heterostructures by wafer bonding. \emph{Nat. Commun.} \textbf{2021} ;
  (b)Roelkens, G.; Zhang, J.; Bogaert, L.; Billet, M.; Wang, D.; Pan,
  B.; Kruckel, C. J.; Soltanian, E.; Maes, D.; Vanackere, T.;
  Vandekerckhove, T.; Cuyvers, S.; De Witte, J.; Lufungula, I. L.; Guo,
  X.; Li, H.; Qin, S.; Muliuk, G.; Uvin, S.; Haq, B.; Op de Beeck, C.;
  Goyvaerts, J.; Lepage, G.; Verheyen, P.; Van Campenhout, J.; Morthier,
  G.; Kuyken, B.; Van Thourhout, D.; Baets, R., Micro-Transfer Printing
  for Heterogeneous Si Photonic Integrated Circuits. \emph{IEEE J. Sel.
  Top. Quantum Electron.} \textbf{2023,} \emph{29} ; (c)Sun, Q.; Zi-Wei
  Yuan; Fan, W.-J.; Li, M.-L.; Fu, W.-X., Low Dielectric
  Benzocyclobutene-type Polymers Based on Facile Synthesis of Linear
  Fluorinated Monomer. \emph{Chin. J. Polym. Sci.} \textbf{2023} .
\item
  Sakai, S., Theoretical studies of the electrocyclic reaction
  mechanisms of o-xylylene to benzocyclobutene. \emph{J. Phys. Chem.
  A}\textbf{2000,} \emph{104} , 11615-11621.
\end{enumerate}\selectlanguage{english}
\begin{longtable}[]{@{}l@{}}
\toprule
Manuscript received: XXXX, 2023 Manuscript revised: XXXX, 2023
Manuscript accepted: XXXX, 2023 Accepted manuscript online: XXXX, 2023
Version of record online: XXXX, 2023\tabularnewline
\bottomrule
\end{longtable}

The Authors\selectlanguage{english}
\begin{longtable}[]{@{}lll@{}}
\toprule
& After acceptance, please insert a group photo of the authors taken
recently. &\tabularnewline
& \textbf{Left to Right:} Ziwei Yuan, Quan Sun, Jinchong Xiao, Pingxia
Zhang, Konstantin S. Levchenko, Dmitry Y. Demin, and Wenxin Fu
&\tabularnewline
\bottomrule
\end{longtable}

\textbf{Entry for the Table of Contents}\selectlanguage{english}
\begin{longtable}[]{@{}l@{}}
\toprule
\textbf{Low-energy driven ring-opening behavior of benzocyclobutene
derivatives} Ziwei Yuan,\textsuperscript{a,c} Quan
Sun,\textsuperscript{a,b} Jinchong Xiao,*\textsuperscript{,c} Pingxia
Zhang,*\textsuperscript{,a} Konstantin S. Levchenko,\textsuperscript{d}
Dmitry Y. Demin,\textsuperscript{d} and Wenxin Fu*\textsuperscript{,a,b}
\emph{Chin. J. Chem.} \textbf{2023}, \emph{41}, XXX---XXX. \textbf{DOI:
10.1002/cjoc.202300XXX}\tabularnewline
The ring-opening behaviors of benzocyclobutene derivatives with one or
two substituents on the four-membered ring were studied by both
theoretical calculation and experimental verification. Their
ring-opening activation energy barriers (\selectlanguage{greek}Δ\selectlanguage{english}G\textsubscript{A}) could be
reduced by 8.2 -- 69 \% lower than unsubstituted one's, which provided a
theoretical basis for developing next-generation low-temperature-curing
low-k materials.\tabularnewline
\bottomrule
\end{longtable}

\selectlanguage{english}
\FloatBarrier
\end{document}

