Database survey
A search of the Cambridge Structural Database (Version 5.38, update November 2016; Groom et al., 2016) for the substructure of 2-(alkylamino)-4-(alkylimino)naphthalen-1(4H)-one yielded 3 hits (we did not restrict the bonds types to the mayor tautomer). Two of the structures, ESOFID (Schweinfurth et al., 2016) and UDAZEF (Singh et al., 2007) use aromatic amines [aniline or substituted aniline] as the amine moiety. Only one structure, UDAZIJ (Singh et al., 2007), uses an aliphatic primary amine (n-butylamine) in the positions 2 and 4. UDAZIJ is noteworthy because the intramolecular N-H•••O bond is 2.34 (2) Å, much longer than compound (I), and that in the crystal lattice of UDAZIJ a dimeric assembly forms held together by intermolecular hydrogen bonding interactions between the N-H and carbonyl of adjoining molecules.
Synthesis and crystallization
The synthesis of (E)-2-(tert-butylamino)-4-(tert-butylimino)naphthalen-1(4H)-one is based on a new procedure (complete publication in progress). A total of 192 mg (1.00 mmol) of 4-chloronaphthalene-1,2-dione and 211 µL (2.00 mmol, 2 equiv.) of tert-butylamine were dissolved in tert-amyl alcohol (3.0 mL). This solution was stirred at 110 °C under a nitrogen atmosphere for 2 hours. After being allowed to cool to room temperature, the green-brownish solution (originally yellow) was diluted with saline water (30 mL) and extracted with ethyl acetate (3 X 20 mL). The combined organic layers were dried over Na2SO4, filtered, and then concentrated under reduced pressure. The crude material (249 mg, a brown dark solid) was separated by silica gel column chromatography using ethyl acetate to obtain the reaction product and the secondary product (compound (I); 119 mg, a dark brown oily solid). Compound (I) was further purified by another silica gel column chromatography using a gradient [100% dichloromethane (CH2Cl2) and then 100% methyl tert-butyl ether (C5H12O)], the fractions were dried under vacuum pressure to yield 14 mg of the pure product (5% yield) as a yellow oily solid. Part of the purified product was re-dissolved in methanol with a few drops of water and placed at room temperature for slow evaporation. After several days, yellow needle-like crystals were obtained. Mp (104-105) °C using a Fisher-Johns with calibrated thermometer; 1H-NMR (600 MHz, CDCl3) δ 8.46-8.48 (dd, J = 7.8, 1.3 Hz, 1 H), 8.09-8.12 (dd, J = 7.8, 1.3 Hz, 1 H), 7.61-7.64 (td, J = 7.8, 1.3 Hz, 1 H), 7.48-7.52 (td, J = 7.8, 1.2 Hz, 1 H), 6.36 (s, 1 H), 5.53 (br. s, 1 H), 1.56 (s, 9 H), 1.47 (s, 9 H).
Refinement details
Crystal data, data collection and structure refinement details are summarized in Table X. All hydrogen atoms are placed in calculated positions [C—H = 0.98–0.99 Å; U iso(H) = 1.2 or 1.5U eq(C)].