1-Phenylisoindole 1 and 2-phenyl-1-phenylimino-2,3-dihydro-1H-isoindole 11 (electron donors) reacted with tetracyanoethyiene (TCNE) and gave 3-dicyanomethyleneisoindole 2 and 1 T phenylisoindol-3one 3. Using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 2,3,5,6-tetrachloro-1,4-benzoquinone (CHL-p) as π-acceptors afforded mainly 3,3'-bisphenylisoindole 4 as well as condensation products. 2,3-Dichloro-1,4-naphthoquinone (DCHNQ) gave miscellaneous reaction products, in addition to the isoindole dimer 4. The two donor systems exhibit, in general, the same behaviour towards the π-acceptors investigated.
Introduction:Among the fused five membered heterocylic systems, indole and isoindole are of interest in connection with our previous investigation on isoindolines (1-5). Whereas indole chemistry has long enjoyed considerable attention, its isomer isoindole, has not received the same interest due to its unstability under normal reaction conditions (6). Consequently, isoindoles are considered as highly reactive intermediates, whose activity, however, may be reduced by substitution in the position three of the five membered ring.
Results and Discussions:As a part of our continuing study in the synthesis of new heterocyclic ring systems via charge-transfer (CT) complexation (7-12), we became interested in employing 1-phenylisoindoles 1 (13) and 2-phenyl-1phenylimino-2,3-dihydro-1H-isoindole 11 (14) as electron donors in donor-acceptor reactions. Our overall strategy is outlined in Schemes 1 and 2.1-Phenyl-3-dicyanomethyleneisoindole 2 and 1-phenylisoindol-3-one 3 (15) were obtained by addition of equimolar amounts of tetracyanoethyiene (TCNE) to 1-phenylisoindole 1 in ethyl acetate, after CT complexes have been formed initially (Scheme 1).On the other hand, upon adding ethyl acetate solutions of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to the solution of donor 1 a pink colour was observed (CT-complex), which rapidly changed to brown for helpful discussions and technical assistance.
Experimental:Melting points are uncorrected. IR spectra (KBr) were obtained on Nicolet 320 FT-IR. 1 H-NMR (400.134MHz.) and 13 C-NMR (100.164 MHz.) spectra were measured on Bruker AM 400 and the chemical shifts were expressed as δ (ppm) using Me 4 Si an internal reference. J values were expressed in Hz. Mass spectra were recorded on a Finnigan MAT 8430 instrument at 70 e.
