Effect of the Structure of 1-Aza-1,3-dienes on 1,2- versus 3,4-Selectivity in Cycloaddition Reactions with Homophthalic Anhydride†

Abstract

The reaction of homophthalic anhydride 1 with N-(cinnamylidene)tritylamine 2a proceeds as a 3,4-cycloaddition to give 4-oxo-1,2,3,4-tetrahydronaphthalene-1-carboxylic acids 3, with N-(cinnamylidene)benzylamine 2b as a 1,2-cycloaddition with the predominant formation of a 1-oxo-1,2,3,4-tetrahydroisoquinoline-4-carboxylic acid, and with either 2a or cinnamaldehyde in the presence of Et ₃ N with the formation of a 2-oxonaphtho[1,2-b]pyran-6-carboxylic acid.