The reactions of 2-alkynylbenzaldehydes with hydrazides: a route to isoquinoline N-imines

Abstract

Sulphonyl- and acyl-hydrazones of 2-ethynylbenzaldehyde cyclise in the presence of base to give Isoquinoline N-imines in moderate yield. The suggested mechanism involves primaryformation ofthe hydrazone anion followed by nucleophilic attack on the alkyne bond, either by the anionic nitrogen to give an unstable 3H-2,3-benzodiazepine which rearranges to the Isoquinoline N-imine, or by the neutral imine nitrogen to give the Isoquinoline system directly. Attempts to extend the reaction to the semicarbazone and 2,4-dinitrophenylhydrazone were not successful.