New short syntheses of isoquinoline-4-carboxylic acid and 2-aza-3,3a-dihydroazulene-3a-carboxylic acid derivatives
Abstract
Cyclopropylideneacetates (2a,b) undergo a formal [2 + 4] cycloaddition with (diphenylmethylene)amine (DPMA-H)(1) to yield dihydro-1-phenylisoquinoline-4-carboxylate (8a) and 1-phenylisoquinoline-4-carboxylate (7b); the Michael adduct of DPMA-H onto (2b), on the other hand, under basic conditions gives 1-phenyl-2-aza-azulene-3a-carboxylate (12) exclusively.