EFFECT OF THE STRUCTURE OF 1-AZA-1,3-DIENES ON 1,2-SELECTIVITY VERSUS3,4-SELECTIVITY IN CYCLOADDITION REACTIONS WITH HOMOPHTHATIC ANHYDRIDE

The reaction of homophthalic anhydride 1 with N-(cinnamylidene)trityta mine 2a proceeds as a 3,4-cycloaddition to give 4-oxo-1,2,3,4-tetrahyd ronaphthalene-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 Et3N with the formation of a 2-oxona phtho[1,2-b]pyran-6-carboxylic acid.