Reactions of diene-conjugated 1,3-dipolar intermediates: the formation of cyclopropa[c]isoquinolines from benzonitrile o-alkenylbenzyl ylides and their rearrangements to benzazepines

Abstract

The diene-conjugsted nitrile ylides 19, generated by the 1,3-dehydrochlorination of imidoyl chlorides 18, cyclise at room temperature to give the cyclopropa[c]isoquinolines 21 in a stereospecific reaction. Thermal decomposition of the latter when R1 or R2= H involves an equilibration between exo and endo isomers (Scheme 4) accompanied by a slower ring expansion to give 1H-2-benzazepines. In cases where neither R1 or R2= H the thermal decomposition follows another path (Scheme 5) to give 5H-2-benzazepines. In contrast 32 and 38, the thiophene analogues of 19, do not give cyclopropa[b]thienopyridines 33 and 39, respectively but instead give the thienoazepines 35 and 41.