The preparation of some 1,7b-disubstituted cyclopropa[c]isoquinolines via nitrile ylide cyclisations and their rearrangement to 2-benzazepines and 4-alkenyl-1,4-dihydroisoquinolines

Abstract

Diene-conjugated nitrile ylides of the type 1a, having substituents other than hydrogen in the R¹ position, cyclise normally to give the C-7b substituted cyclopropa[c]isoquinolines 2a. In cases where R² or R³ = H the latter undergo the usual thermal rearrangement to give 5-substituted 2-benzazepines 5a. However, when R² and R³ ≠ H and either is a CH₃ group, then the presence of the C-7b substituent in 2a diverts the thermal rearrangement into a new reaction path leading to the formation of 1,4-dihydro-4-alkenylisoquinolines 14 in high yield.