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\begin{document}

\title{Cobalt-Catalyzed Switchable {[}4 + 1{]} and {[}4 + 1 + 1{]}
Spirocyclization of Aromatic Amides with
2-Diazo-1H-indene-1,3(2H)-dione: Access to Spiro
Indene-2,1'-isoindolinones and Spiro Isochro-man-3,1'-isoindolinones}



\author[1]{Bin Li}%
\author[1]{Mengmeng Xie}%
\author[1]{Jingyu Li}%
\author[1]{Nana Shen}%
\author[1]{Xinying Zhang}%
\author[1]{Xuesen Fan}%
\affil[1]{Henan Normal University}%


\vspace{-1em}



  
  \date{May 17, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Herein we report a condition-controlled divergent synthesis of spiro
indene-2,1'-isoindolinones and spiro isochroman-3,1'-isoindolinones
through cobalt-catalyzed formal {[}4 + 1{]} and {[}4 + 1 + 1{]}
spirocyclization of aromatic amides with
2-diazo-1H-indene-1,3(2H)-dione. When the reaction is carried out under
air in ethyl acetate, spiro indene-2,1'-isoindolinones are formed
through Co(II)-catalyzed C-H/N-H {[}4 + 1{]} spirocyclization. When the
reaction is run under O2 in CH3CN, on the other hand, spiro
isochroman-3,1'-isoindolinones are generated through Baeyer-Villiger
oxidation of the in situ formed spiro indene-2,1'-isoindolinones with O2
as a cheaper and environmental-friendly oxygen source. In general, these
protocols have advantages such as using non-precious and earth-abundant
metal catalyst, no extra additive, high efficiency and regioselectivity.
A gram-scale synthesis and the removal of the directing group further
highlight its utility.%
\end{abstract}%



\sloppy


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

Cobalt-Catalyzed Switchable {[}4 + 1{]} and {[}4 + 1 + 1{]}
Spirocyclization of Aromatic Amides with 2-Diazo-1\emph{H}
-indene-1,3(2\emph{H} )-dione: Access to Spiro
Indene-2,1'-isoindolinones and Spiro Isochroman-3,1'-isoindolinones

Bin Li*, Mengmeng Xie, Jingyu Li, Nana Shen, Xinying Zhang, and Xuesen
Fan*

Pingyuan Laboratory, Key Laboratory of Green Chemical Media and
Reactions, Key Laboratory for Yellow River and Huai River Water
Environmental Pollution Control, Ministry of Education, School of
Environment, School of Chemistry and Chemical Engineering, Henan Normal
University, Xinxiang, Henan 453007, P. R. China.\selectlanguage{english}
\begin{longtable}[]{@{}l@{}}
\toprule
\textbf{Keywords}\tabularnewline
\midrule
\endhead
Spiro indene-2,1'-isoindolinones \textbar{} Spiro
isochroman-3,1'-isoindolinones \textbar{} Cobalt-catalyzed \textbar{}
Switchable {[}4 + 1{]} and {[}4 + 1 + 1{]} spirocyclization \textbar{}
Aromatic amides \textbar{}
2-Diazo-1\emph{H}-indene-1,3(2\emph{H})-dione\tabularnewline
\textbf{Comprehensive Summary}\tabularnewline
Herein we report a condition-controlled divergent synthesis of spiro
indene-2,1'-isoindolinones and spiro isochroman-3,1'-isoindolinones
through cobalt-catalyzed formal {[}4 + 1{]} and {[}4 + 1 + 1{]}
spirocyclization of aromatic amides with
2-diazo-1\emph{H}-indene-1,3(2\emph{H})-dione. When the reaction is
carried out under air in ethyl acetate, spiro indene-2,1'-isoindolinones
are formed through Co(II)-catalyzed C-H/N-H {[}4 + 1{]}
spirocyclization. When the reaction is run under O\textsubscript{2} in
CH\textsubscript{3}CN, on the other hand, spiro
isochroman-3,1'-isoindolinones are generated through Baeyer-Villiger
oxidation of the in situ formed spiro indene-2,1'-isoindolinones with
O\textsubscript{2} as a cheaper and environmental-friendly oxygen
source. In general, these protocols have advantages such as using
non-precious and earth-abundant metal catalyst, no extra additive, high
efficiency and regioselectivity. A gram-scale synthesis and the removal
of the directing group further highlight its utility.\tabularnewline
\bottomrule
\end{longtable}

\section*{}

{\label{section}}

Background and Originality Content

Spirocyclic skeletons have attracted tremendous interest among synthetic
and medicinal chemists, not only due to their peculiar high rigidity and
unique three-dimensional geometries, but also because they are
ubiquitous in natural products and possess multiple pharmaceutical
activities.\textsuperscript{{[}1{]}} In particular, spiro-isoindolinone
is an important scaffold that constitutes the core structure in
biologically active molecules endowed with anticancer, aldose reductase
inhibiting, and TNF-\selectlanguage{greek}α \selectlanguage{english}inhibiting activities (Figure
1).\textsuperscript{{[}2{]}} Owing to its significance, the development
of practical and economical methods for the preparation of
spiro-isoindolinone derivatives have always attracted considerable
interest for the synthetic community.\textsuperscript{{[}3{]}}

\textbf{Figure 1} Bioactive molecules containing spiro isoindolinone
moieties.

In recent years, directing group-assisted C-H bond activation (CHA)
strategy catalyzed by transition metal (TM) has evolved into one of the
practical tools for the construction of C-C and C-heteroatom bond due to
its excellent atom- and step-economy.\textsuperscript{{[}4{]}} In
particular, as the high natural abundance of the first row (3d)
transition metals renders the catalytic process cost-effective, it is a
great privilege to develop earth-abundant metal-catalyzed inert CHA
system performing reactions with common
substrates.\textsuperscript{{[}5{]}} In this regard, cobalt has emerged
as a versatile, efficient and less toxic metal-catalyst for CHA to
construct polycyclic molecular frameworks.\textsuperscript{{[}5-6{]}} On
the other hand, \emph{a} -diazo carbonyl compounds have been frequently
used as intriguing coupling partners in CHA through dediazonization to
generate metal-carbene species with high flexibility and diverse
reactivity for the synthesis of various organic functional
molecules.\textsuperscript{{[}7{]}} However, cobalt-catalyzed CHA
carbene insertion reaction has not been well exploited owing to lack of
efficient catalytic systems, and most of these transformations were
promoted by cyclopentadienyl (Cp*) Co(III) complexes, rather than cheap
and commercially available cobalt salt. Based on the fact that
8-aminoquinoline moiety are effective bidentate directing group and can
be conveniently removed, it has been used as a popular directing group
in TM-catalyzed CHA reactions.\textsuperscript{{[}8{]}} Recently, Li and
co-workers developed a unique strategy to provide a controllable \selectlanguage{greek}α- \selectlanguage{english}or
\selectlanguage{greek}β-\selectlanguage{english}functionalization of \selectlanguage{greek}α-\selectlanguage{english}diazoketones with aromatic amides for the
synthesis of isoindolinones via using a non-Cp* cobalt catalyst under
ligand-free conditions (Scheme 1a).\textsuperscript{{[}9{]}} Very
recently, Song's group disclosed an efficient
Co(acac)\textsubscript{2}catalyzed three-component coupling of
benzamides with diazo compounds and \emph{tert} -butyl hydroperoxide,
providing products with a quaternary carbon center in moderate to
excellent yields (Scheme 1b).\textsuperscript{{[}10{]}} However, the
cobalt-catalyzed C-H bond activation/spiroannulation reaction using
diazo compound as carbene precursor to construct spirocyclic framework
has not been reported. Enlightened by the aforementioned research and as
a continuation of our interest in TM-catalyzed
CHA\textsuperscript{{[}11{]}} and diazo
chemistry,\textsuperscript{{[}12{]}} we envisaged a tentative plan to
obtain spiro indene-2,1'-isoindolinones from Co-catalyzed {[}4 + 1{]}
spiroannulation reaction of aromatic amides with 2-diazo-1\emph{H}
-indene-1,3(2\emph{H} )-dione. Experimental studies showed that the
reaction could selectively furnish the initially designed spirocyclic
product through {[}4 + 1{]} spiroannulation or the unexpected spiro
isochroman-3,1'-isoindolinone derivative through {[}4 + 1 + 1{]}
oxidative spirocyclization under different reaction conditions. Notably,
the formation of spiro isochroman-3,1'-isoindolinone derivatives should
involve a Baeyer-Villiger oxidation of the in situ formed spiro
indene-2,1'-isoindolinones with O\textsubscript{2} as a cheaper and
cleaner oxygen source (Scheme 1c). It is worth mentioning that
{[}Cp*RhCl\textsubscript{2}{]}\textsubscript{2},
{[}Cp*IrCl\textsubscript{2}{]}\textsubscript{2} and {[}Ru(\emph{p}
-cymene)Cl\textsubscript{2}{]}\textsubscript{2} were found to be
inactive in the oxidative spiroannulation process. To the best of our
knowledge, such reaction patterns have not been disclosed previously.
Herein, we would like to report the detailed results.

\textbf{Scheme 1} Co-catalyzed CHA of aromatic amides with diazo
compounds

Results and Discussion

At the outset of our studies, the reaction feasibility was tested using
8-aminoquinolinebenzamide (\textbf{1a} ) with 2-diazo-1\emph{H} -indene-
1,3(2\emph{H} )-dione (\textbf{2} ) as the model substrates in the
presence of 10 mol \%
{[}Cp*Co(CO)I\textsubscript{2}{]}\textsubscript{2}and 2 equiv. of
Ag\textsubscript{2}CO\textsubscript{3} in 1,2-dichloroethane (DCE) at
100 \selectlanguage{ngerman}°C for 15 h (Table 1, entry 1). It is gratifying that the desired
product was obtained in 18\% yield as a white solid. Inspired by this
positive result, we then screened other simple cobalt salts including
Co(OAc)\textsubscript{2}, Co(acac)\textsubscript{2},
Co(acac)\textsubscript{3} and
Co(NO\textsubscript{3})\textsubscript{2}\textbf{·} 6H\textsubscript{2}O
(Table 1, entries 2-5). Among them, Co(acac)\textsubscript{2} was the
most effective catalyst that outperformed others to deliver
\textbf{3a}in 86\% yield. Subsequently, we tested various solvents
(toluene, CH\textsubscript{3}CN, tetrahydrofuran (THF), dioxane, ethyl
acetate (EA), CH\textsubscript{3}OH) as alternative solvents, and the
results confirmed that EA was the most appropriate solvent for this {[}4
+ 1{]} oxidative spirocyclization (Table 1, entries 6-11). Next,
Ag\textsubscript{2}O, AgOAc, Cu(OAc)\textsubscript{2} and
Mn(OAc)\textsubscript{2} were tried as oxidant in place of
Ag\textsubscript{2}CO\textsubscript{3}. It turned out that they were
less effective (Table 1, entries 12-15). As for the loading of oxidant,
we found that using 3 equiv. of
Ag\textsubscript{2}CO\textsubscript{3}increased the yield of \textbf{3a}
to 97\% (Table 1, entries 16-17). Moreover, decreasing or increasing the
reaction temperature did not give better yield of \textbf{3a} (Table 1,
entries 18-19). Furthermore, it should be noted that the reaction run in
CH\textsubscript{3}CN or dioxane not only afford \textbf{3a} in 57\% and
73\% yields, but also generate another unexpected spiro product
\textbf{4a} in 26\% and 19\% yields, respectively (Table 1, entries 7
and 9). It should be noteworthy that the structure of \textbf{4a} was
ascertained by X-ray single-crystal diffraction (see the SI). This
interesting result prompted us to have a further optimization study with
the prospect to find suitable reaction conditions to realize selective
and efficient synthesis of \textbf{4a} . When the reaction was carried
out in the presence of 3 equiv. of oxidant in CH\textsubscript{3}CN for
24 h, the yield of \textbf{4a} increased to 41\% (Table 1, entry 20).
Other oxidant such as 2,2,6,6-tetramethylpiperidine-1-oxyl
(TEMPO),\emph{tert} -butyl hydroperoxide (TBHP) and
K\textsubscript{2}S\textsubscript{2}O\textsubscript{8} were found to be
ineffective and delivered only product \textbf{3a} (Table 1, entries
21-23). To our delight, when this {[}4 + 1 +1{]} oxidative
spirocyclization reaction was carried out under an oxygen
atmosphere,\textbf{4a} was generated in 78\% yield. In this case, only
trace amount of \textbf{3a} was detected (Table 1, entry 24).

\textbf{Table 1} Optimization studies on the formation of \textbf{3a}and
\textbf{4a} \emph{\textsuperscript{a}}\selectlanguage{english}
\begin{longtable}[]{@{}llllll@{}}
\toprule
Entry & Catalyst & Oxidant (eq.) & Solvent & Yield
(\%)\emph{\textsuperscript{b}} & Yield
(\%)\emph{\textsuperscript{b}}\tabularnewline
\midrule
\endhead
& & & & \textbf{3a} & \textbf{4a}\tabularnewline
1\emph{\textsuperscript{c}} &
{[}Cp*Co(CO)I\textsubscript{2}{]}\textsubscript{2} &
Ag\textsubscript{2}CO\textsubscript{3} (2) & DCE & 18 & 0\tabularnewline
2 & Co(OAc)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(2) & DCE & 75 & 0\tabularnewline
3 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(2) & DCE & 86 & 0\tabularnewline
4 & Co(acac)\textsubscript{3} & Ag\textsubscript{2}CO\textsubscript{3}
(2) & DCE & 84 & 0\tabularnewline
5 &
Co(NO\textsubscript{3})\textsubscript{2}\selectlanguage{ngerman}\textbf{·}6H\textsubscript{2}O &
Ag\textsubscript{2}CO\textsubscript{3} (2) & DCE & 16 & 0\tabularnewline
6 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(2) & Toluene & 78 & 0\tabularnewline
7 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(2) & CH\textsubscript{3}CN & 57 & 26\tabularnewline
8 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(2) & THF & 51 & trace\tabularnewline
9 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(2) & Dioxane & 73 & 19\tabularnewline
10 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(2) & EA & 89 & trace\tabularnewline
11 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(2) & CH\textsubscript{3}OH & 0 & 0\tabularnewline
12 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}O (2) & EA & 50 &
trace\tabularnewline
13 & Co(acac)\textsubscript{2} & AgOAc (4) & EA & 65 &
trace\tabularnewline
14 & Co(acac)\textsubscript{2} & Cu(OAc)\textsubscript{2} (4) & EA & 0 &
0\tabularnewline
15 & Co(acac)\textsubscript{2} & Mn(OAc)\textsubscript{2} (2) & EA & 51
& 0\tabularnewline
16 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(1) & EA & 68 & 0\tabularnewline
17 & Co(acac)\textsubscript{2} & Ag\textsubscript{2}CO\textsubscript{3}
(3) & EA & 97 & 0\tabularnewline
18\emph{\textsuperscript{d}} & Co(acac)\textsubscript{2} &
Ag\textsubscript{2}CO\textsubscript{3} (3) & EA & 85 & 0\tabularnewline
19\emph{\textsuperscript{e}} & Co(acac)\textsubscript{2} &
Ag\textsubscript{2}CO\textsubscript{3} (3) & EA & 90 & 0\tabularnewline
20\emph{\textsuperscript{f}} & Co(acac)\textsubscript{2} &
Ag\textsubscript{2}CO\textsubscript{3} (3) & CH\textsubscript{3}CN & 49
& 41\tabularnewline
21\emph{\textsuperscript{f}} & Co(acac)\textsubscript{2} & TEMPO (3) &
CH\textsubscript{3}CN & 19 & 0\tabularnewline
22\emph{\textsuperscript{f}} & Co(acac)\textsubscript{2} & TBHP (3) &
CH\textsubscript{3}CN & 81 & 0\tabularnewline
23\emph{\textsuperscript{f}} & Co(acac)\textsubscript{2} &
K\textsubscript{2}S\textsubscript{2}O\textsubscript{8} (3) &
CH\textsubscript{3}CN & 36 & 0\tabularnewline
24\emph{\textsuperscript{f g}} & Co(acac)\textsubscript{2} &
Ag\textsubscript{2}CO\textsubscript{3} (3) & CH\textsubscript{3}CN &
trace & 78\tabularnewline
\bottomrule
\end{longtable}

\emph{\textsuperscript{a}} Reaction conditions: Unless otherwise
mentioned, 0.2 mmol of \textbf{1a} , 0.3 mmol of \textbf{2} , 0.04 mmol
of catalyst, 1.5 mL of solvent, 100 \selectlanguage{ngerman}°C, air, 15
h.\emph{\textsuperscript{b}} Isolated yields.
\emph{\textsuperscript{c}}0.01 mmol of catalyst was used.
\emph{\textsuperscript{d}} 80 °C.\emph{\textsuperscript{e}} 120 °C.
\emph{\textsuperscript{f}} 24 h.\emph{\textsuperscript{g}} Under
O\textsubscript{2}.

With the optimal reaction conditions in hand, we first studied the
substrate scope of the {[}4 + 1{]} spirocyclization reaction by reacting
various aromatic amides (\textbf{1} ) with \textbf{2} (Scheme 2). The
results demonstrated that substrate \textbf{1} with either an
electron-donating group (EDG) such as methoxy, \emph{tert} -butyl,
methyl and phenyl or electron-withdrawing group (EWG) such as halides,
trifluoromethyl as the R\textsuperscript{1} unit attached on the
4-pisition of the phenyl ring worked smoothly to give the desired
products (\textbf{3b} -\textbf{3i} ) in good to excellent yields. In
following study, it was found that substrates \textbf{1} bearing 3-
methoxy, 3-methyl, 3-chloro and 3-bromo substituted phenyl scaffold
coupled readily with \textbf{2} , delivering products\textbf{3j}
-\textbf{3m} in good yields, respectively, at the less hindered position
in a highly regioselective manner. The structure of\textbf{3k} was
confirmed by single-crystal X-ray diffraction analysis (see the SI).
Moreover, the reaction of substrates \textbf{1} having 2-methyl,
2-chloro or 2-bromo substituted phenyl ring with \textbf{2}afforded the
corresponding {[}4 + 1{]} spiroannulation products in diminished yields
probably due to the steric perturbation of these substrates (\textbf{3n}
-\textbf{3p} ). Additionally, the reaction of\emph{N}
-(quinolin-8-yl)-2-naph- thamide and\emph{N}
-(quinolin-8-yl)-1-naphthamide with \textbf{2} also proceeded smoothly
to generate \textbf{3q} and \textbf{3r} in 89\% and 54\% yields,
respectively. Furthermore, we were pleased to find that
5-methoxyquinolin-8-amine and 5-chloroquinolin- 8-amine as directing
groups were also compatible with this transformation to
afford\textbf{3s} and \textbf{3t} in good yields. Unfortunately,
2-methoxy-\emph{N} -(quinolin-8-yl)benzamide and\emph{N}
-(quinolin-8-yl)furan -2-carboxamide failed to provide the desired
product, presumably because of the coordination of the oxygen with the
Co-catalyst. In addition, 2-diazocyclopentane-1,3-dione and
2-diazocyclohexane- 1,3-dione could not participate in this reaction
under the standard conditions.

\textbf{Scheme 2} Substrate scope for the synthesis of\textbf{3}
\textsuperscript{\emph{a} ,\emph{b}}

\emph{\textsuperscript{a}} Reaction conditions: Unless otherwise
mentioned, 0.2 mmol of \textbf{1a} , 0.3 mmol of \textbf{2} , 0.04 mmol
of Co(acac)\textsubscript{2}, 0.6 mmol of
Ag\textsubscript{2}CO\textsubscript{3}, 1.5 mL of EtOAc, 100 °C, air, 15
h. \emph{\textsuperscript{b}} Isolated yields.\emph{\textsuperscript{c}}
under Ar.

Next, we investigated the substrate scope of the {[}4 + 1 + 1{]}
spirocyclization reaction for the preparation of spiro
isochroman-3,1'-isoindolinone \textbf{4} (Scheme 3). Various aromatic
amides \textbf{1} bearing diverse functional groups such as
methoxy,\emph{tert} -butyl, methyl, phenyl fluoro, chloro, or bromo,
trifluoromethyl on the \emph{para} -, \emph{meta} -, or \emph{ortho}
-site of phenyl moiety smoothly underwent the {[}4 + 1 + 1{]}
spirocyclization reactions, delivering products \textbf{4b} -\textbf{4p}
in moderate to good yields. Of note, 2-methyl, 2-fluoro, 2-chloro, or
2-bromo substituted \emph{N} -(quinolin-8-yl)benzamides reacted with
\textbf{2}under standard conditions for the formation of \textbf{4a} ,
furnishing the corresponding products \textbf{4m} -\textbf{4p} in
58-70\% yields. We assumed that under the conditions of generating
\textbf{4} , the solvent CH\textsubscript{3}CN could replace
quinolin-8-amine serve as a ligand for the Co-catalyst, reducing the
influence of steric hindrance effect. To our delight, the developed
methodology is also applicable for\emph{N}
-(quinolin-8-yl)-1-naphthamide,\emph{N} -(5-methoxyquinolin-8-yl)
benzamide and\emph{N} -(5-chloroquinolin-8-yl)benzamide giving
corresponding annulated product \textbf{4q} -\textbf{4s} in good yields.

In order to get more insights into the reaction mechanism, a series of
control experiments were conducted (Scheme 4). First, deuterium
incorporation experiments were performed by treating \textbf{1a} with
CD\textsubscript{3}OD or D\textsubscript{2}O under the standard
conditions for \textbf{3a} , and the results showed that no H/D exchange
was detected. Furthermore, the same results were observed when
treating\textbf{1a} and \textbf{2} with CD\textsubscript{3}OD or
D\textsubscript{2}O under the standard conditions. These results
indicated that the C\selectlanguage{english}-H bond cleavage is irreversible (Scheme 4a).
Second, the intermolecular competition reaction of the 1:1

\textbf{Scheme 3} Substrate scope for the synthesis of\textbf{4}
\textsuperscript{\emph{a} ,\emph{b}}

\emph{\textsuperscript{a}} Reaction conditions: 0.2 mmol of \textbf{1a}
, 0.3 mmol of \textbf{2a} , 0.04 mmol of Co(acac)\textsubscript{2}, 0.6
mmol of Ag\textsubscript{2}CO\textsubscript{3}, 1.5 mL of
CH\textsubscript{3}CN, 100 degC, O\textsubscript{2}, 24
h.\emph{\textsuperscript{b}} Isolated yields.

mixture of methoxy substituted benzamide (\textbf{1b} ) and
trifluoromethyl substituted benzamide (\textbf{1i} ) with \textbf{2}
gave a mixture of \textbf{3b} and \textbf{3i} in 18\% and 17\% yields,
respectively. This outcome suggests that electron-rich substrate is
slightly favorable for this reaction than an electron-deficient one
(Scheme 4b). Third, an intermolecular competitive reaction was performed
by treating an equimolar mixture of \textbf{1a}
and\textbf{1a-\emph{d}\textsubscript{5}} with \textbf{2} , from
which\textbf{3a} and \textbf{3a-\emph{d}\textsubscript{4}} were gained
in a ratio of 0.53:0.47 upon analyzing \textsuperscript{1}H NMR spectra,
and competitive kinetic isotope effect (KIE) value of 1.13 was
calculated, revealing that the C(sp\textsuperscript{2})\selectlanguage{english}-H bond
activation might not be involved in the turnover-limiting step (Scheme
4c).

Furthermore, to testing the proposal that \textbf{4a} might be formed
through transformation of \textbf{3a} , we performed a series of control
experiments (Scheme 5). Firstly, \textbf{3a} was subjected to the
standard reaction conditions for the formation of \textbf{4a} ,
affording\textbf{4a} in 87\% yield. In contrast, under Ar atmosphere,
\textbf{4a}was not observed (Scheme 5a and 5b). Secondly, \textbf{4a}
was generated in 84\% yield in the presence of 0.5 eq.
Ag\textsubscript{2}CO\textsubscript{3} and O\textsubscript{2}. However,
no desired product was yielded in the absence silver salt (Scheme 5c and
5d). Finally, \textbf{3a} could not be converted \textbf{4a} under
standard conditions in the presence of radical scavengers such as TEMPO
and BHT (2,6-di-tert-butyl-4-methylphenol) (Scheme 5e). These results
showed that \textbf{4a} was formed by oxygen participation in
Baeyer-Villiger oxidation of \textbf{3a} promoted by
Ag\textsuperscript{+}.

On the basis of control experiments and known
reports,\textsuperscript{{[}9-13{]}} a plausible mechanism for the
cobalt-catalyzed {[}4 + 1{]} and {[}4 + 1 + 1{]} spirocyclization
reactions have been depicted in Scheme 6. At first, the coordination of
the two nitrogen atom of \textbf{1a} to a Co(III) complex generated via
oxidant by Ag\textsubscript{2}CO\textsubscript{3} forms the
five-membered cobaltacycle intermediate \textbf{I} , which undergoes the
concerted metalation-deprotonation pathway to give
intermediate\textbf{II} . The coordination of \textbf{2} to the metal
center in\textbf{II} followed by release of N\textsubscript{2} affords
the cobalt-carbene species intermediate \textbf{III} . Subsequently,

\textbf{Scheme 4} Mechanistic studies (I)

\textbf{Scheme 5} Mechanistic studies (II)

the migratory insertion yields intermediate \textbf{IV} , which
undergoes reductive elimination to form the {[}4 + 1{]} spirocyclization
product\textbf{3a} and delivers Co(I) complex, which is then reoxidized
to regenerate the active Co(III) species. In another aspect, under the
promotion of Ag\textsuperscript{+} and O\textsubscript{2}, the in situ
formed \textbf{3a} undergoes a Baeyer-Villiger oxidation to generate the
product \textbf{4a} .\textsuperscript{{[}13{]}}

To demonstrate the synthetic utility of the current protocol, the large
scale experiment and directing group removal experiment were performed.
As shown in Scheme 7a and 7b, a mixture of \textbf{1a} (3 mmol)
and\textbf{2a} (4.5 mmol) was subjected to the aforementioned both
standard reaction conditions, yielding the {[}4 + 1{]} and {[}4 + 1 +
1{]} spirocyclization products \textbf{3a} and \textbf{4a} in 80\% and
62\% yields, respectively. On the other hand, \textbf{3s} and
\textbf{4r}could be easily transformed into
spiro{[}indene-2,1'-isoindoline{]}-1,3,3'-trione \textbf{5} and
spiro{[}isochroman-3,1'-isoindoline{]}-1,3',4-trione \textbf{6} through
removing the 5-methoxyquinolin-8-amine directing group in moderate
overall yields, respectively (Scheme 8).

\textbf{Scheme 6} Proposed mechanism

\textbf{Scheme 7} Enlarged scale synthesis of \textbf{3a} and

\textbf{5a}

\textbf{Scheme 8} Removal of directing group

Conclusions

In summary, we have reported condition controlled Co(II)-catalyzed
selective {[}4 + 1{]} and {[}4 + 1 + 1{]} spirocyclization reactions of
aromatic amides with 2-diazo-1\emph{H} -indene-1,3(2\emph{H} )-dione
leading to the construction of spiro indene-2,1'-isoindolinones and
spiro isochroman-3,1'-isoindolinones. This current protocol features
with earth-abundant and cheap metal catalyst, avoidance of external
additives, low-cost, clean and abundant oxygen source, and valuable
products with moderate to excellent yields. Moreover, gram-scale
synthesis and the removal of the directing group further demonstrate the
practicability of this protocol to potential industrial applications.

Experimental

\textbf{General procedure for the synthesis of 3}

To a reaction tube equipped with a stir bar were added\emph{N}
-(quinolin-8-yl)benzamide (\textbf{1a} , 50 mg, 0.2 mmol),
2-diazo-1\emph{H} -indene-1,3(2\emph{H} )-dione (\textbf{2} , 52 mg, 0.3
mmol), Co(acac)\textsubscript{2} (10 mg, 0.04 mmol),
Ag\textsubscript{2}CO\textsubscript{3} (165 mg, 0.6 mmol) and ethyl
acetate (1.5 mL). The tube was then sealed, and the mixture was stirred
at 100 degC (metal module heating) under air for 15 h. Upon completion, it
was cooled to room temperature, filtered through a pad of celite, and
concentrated under reduced pressure. The residue was purified by silica
gel column chromatography using petroleum ether/ethyl acetate (3:1) as
eluent to afford \textbf{3a} . Other products \textbf{3b}
-\textbf{3t}were obtained in a similar manner.

\textbf{General procedure for the synthesis of 4}

To a reaction tube equipped with a stir bar were added\emph{N}
-(quinolin-8-yl)benzamide (\textbf{1a} , 50 mg, 0.2 mmol),
2-diazo-1\emph{H} -indene-1,3(2\emph{H} )-dione (\textbf{2} , 52 mg, 0.3
mmol), Co(acac)\textsubscript{2} (10 mg, 0.04 mmol),
Ag\textsubscript{2}CO\textsubscript{3} (165 mg, 0.6 mmol) and
CH\textsubscript{3}CN (1.5 mL). The tube was then sealed, and the
mixture was stirred at 100 degC (metal module heating) under
O\textsubscript{2} for 24 h. Upon completion, it was cooled to room
temperature, filtered through a pad of celite, and concentrated under
reduced pressure. The residue was purified by silica gel column
chromatography using petroleum ether/ethyl acetate (3:1) as eluent to
afford \textbf{4a} . Other products \textbf{4a-4s} were obtained in a
similar manner.

\textbf{Synthesis of spiro{[}indene-2,1'-isoindoline{]}-1,3,3'-trione
(5)}

i) 2'-(5-Methoxyquinolin-8-yl)spiro{[}indene-2,1'-isoindoline{]}-
1,3,3'-trione (\textbf{3s} , 84 mg, 0.2 mmol) was placed in a 10 mL
two-necked reaction flask, which was filled with nitrogen by using the
standard Schlenk technique. DCM (1.0 mL) was sequentially injected via a
syringe. To the suspension was added BBr\textsubscript{3} (0.24 mL, 1M
in THF, 0.24 mmol) at 0 degC (ice-water bath). The mixture was stirred at
0 degC (ice-water bath) for 5 min and then allowed to warm to room
temperature for 18 h. The resulting mixture was quenched with water at 0
degC and extracted with ethyl acetate three times. The combined organic
layer was washed with water and dried over anhydrous
Na\textsubscript{2}SO\textsubscript{4}.

ii) The crude product dissolved in MeCN/H\textsubscript{2}O
(MeCN/H\textsubscript{2}O = 4:1, 2 mL),
Ce(NH\textsubscript{4})\textsubscript{2}(NO\textsubscript{3})\textsubscript{6}(CAN,
658 mg, 1.2 mmol) was added to the mixture with a portion at room
temperature, and the mixture was stirred for 12 h at 60 degC (oil bath).
After the reation completed, H\textsubscript{2}O (5 mL) was added and
the mixture was extracted with ethyl acetate (3 mL x3). Combined organic
phase was dried over anhydrous Na\textsubscript{2}SO\textsubscript{4},
filtered through Celite and the filtrate was concentrated. The crude
residue was purified by flash chromatography in petroleum ether:ethyl
acetate= 1:1 to give \textbf{5} as white soild (27 mg, 51\%).

\textbf{Synthesis of
spiro{[}isochroman-3,1'-isoindoline{]}-1,3',4-trione (6)}

i) 2'-(5-methoxyquinolin-8-yl)spiro{[}isochroman-3,1'-isoindo-
line{]}-1,3',4-trione (\textbf{4r} , 87 mg, 0.2 mmol) was placed in a 10
mL two-necked reaction flask, which was filled with nitrogen by using
the standard Schlenk technique. DCM (1.0 mL) was sequentially injected
via a syringe. To the suspension was added BBr\textsubscript{3} (0.24
mL, 1M in THF, 0.24 mmol) at 0 degC (ice-water bath). The mixture was
stirred at 0 degC (ice-water bath) for 5 min and then allowed to warm to
room temperature for 18 h. The resulting mixture was quenched with water
at 0 degC and extracted with ethyl acetate three times. The combined
organic layer was washed with water and dried over anhydrous
Na\textsubscript{2}SO\textsubscript{4}.

ii) The crude product dissolved in MeCN/H\textsubscript{2}O
(MeCN/H\textsubscript{2}O = 4:1, 2 mL),
Ce(NH\textsubscript{4})\textsubscript{2}(NO\textsubscript{3})\textsubscript{6}(CAN,
658 mg, 1.2 mmol) was added to the mixture with a portion at room
temperature, and the mixture was stirred for 12 h at 60 degC (oil bath).
After the reation completed, H\textsubscript{2}O (5 mL) was added and
the mixture was extracted with ethyl acetate (3 mL x3). Combined organic
phase was dried over anhydrous Na\textsubscript{2}SO\textsubscript{4},
filtered through Celite and the filtrate was concentrated. The crude
residue was purified by flash chromatography in petroleum ether:ethyl
acetate= 1:1 to give \textbf{6} as white soild (25 mg, 45\%).

Supporting Information

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

Acknowledgement

We are grateful to the National Natural Science Foundation of China
(22101075, U2004189), Central Plains Science and Technology Innovation
Leader Project (224200510009), Postdoctoral Research Grant in Henan
Province (202103085), Henan Key Laboratory of Organic Functional
Molecules and Drug Innovation, and 111 Project (D17007) for financial
support.

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\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:} Authors Names &\tabularnewline
\bottomrule
\end{longtable}

\textbf{Entry for the Table of Contents}\selectlanguage{english}
\begin{longtable}[]{@{}l@{}}
\toprule
\textbf{Cobalt-Catalyzed Switchable {[}4 + 1{]} and {[}4 + 1 + 1{]}
Spirocyclization of Aromatic Amides with
2-Diazo-1\emph{H}-indene-1,3(2\emph{H})-dione: Access to Spiro
Indene-2,1'-isoindolinones and Spiro Isochroman-3,1'-isoindolinones}
Author, Corresponding Author,* and Author \emph{Chin. J. Chem.}
\textbf{2023}, \emph{41}, XXX---XXX. \textbf{DOI:
10.1002/cjoc.202300XXX}\tabularnewline
Herein we report a condition-controlled divergent synthesis of spiro
indene-2,1'-isoindolinones and spiro isochroman-3,1'-isoindolinones
through cobalt-catalyzed formal {[}4 + 1{]} and {[}4 + 1 + 1{]}
spirocyclization of aromatic amides with
2-diazo-1\emph{H}-indene-1,3(2\emph{H})-dione.\tabularnewline
\bottomrule
\end{longtable}

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