Reactions of diene-conjugated 1,3-dipolar intermediates: a versatile and efficient route to dibenz[c,e]azepines via benzonitrile o-arylbenzyl ylides

Abstract

Diene-conjugated nitrile ylides of the type 1 in which both the α,β- and the γδ-double bonds are aromatic, and where R is either hydrogen or a para substituent, cyclise to give dibenz[c,e]azepines 21(Scheme 2) in high yield. This is in contrast to the analogous diazo system 2 in which cyclisation does not occur. The presence of an ortho methyl group in the ring under attack (1j, Scheme 3) prevents cyclisation via its steric limitation of conjugation in the transition state.