Studies on heterocyclic analogues of azulene. Part 2. Cycloaddition reactions of aza-analogues of azulene with dimethyl acetylenedicarboxylate: intermediacy of a 1,8-dipolar species

Abstract

Cyclohepta[b]pyrroles (1) and cycloheptimidazole (2) react with dimethyl acetylenedicarboxylate to give 2H-2a-azacyclopent[cd]azulenes (3) and 3H-2a-azacyclopenta[ef]heptalenes (4), and 3H-1,2a-diazacyclopenta[ef]-heptalene (5), respectively, in low to moderate yields. The formation of these products is explained in terms of 1,8-dipolar cycloaddition reactions.