8b,8c-Diazapyracylenes

Scheme 5 shows another synthetic sequence, which has led to the formation of 3,8-dicyano-8b,8c-diazapyracylene (92b).112... 

Two possible structures may be proposed for 8b,8c-diazapyracylene an MAT-bipyrryl core with two vinyl bridges (97a) and a cyclodo-... 

Ester groups, on the other hand, exert a sti ong effect on the shift of all protons of cycl[3,3,3]azines (2) (A = 2.49-4.70 ppm, see Table IV) thus demonstrating the greater importance of the 12 7r-perimeter as outlined in Section V. The chemical properties of the 8b,8c-diazapyracylene (92a) are consistent with the anticipated structure. Hydrogenation takes place only in the 3,4- and 7,8-positions to give 91a and 91b.,° 111... 

The two different routes which have been reported a (74JA6132) b (77CB2765)) for the synthesis of 8b,8c-diazapyracylenes (306) are shown in Scheme 47. 

The analogous structure 97a may be the most adequate representation for 8b,8c-diazapyracylenes since the interaction energy of the 14 r-periphery could hardly be sufficient to overcome the energy required for charge separation in 97b. The properties of diazapyracylenes (92) might be affected by a remarkable strain energy which has been calculated to be 52.6 kcal mol for the closely related pyracylene" 92a has been shown to be planar by X-ray analysis. "... 

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