Syntheses and cycloadditions of ethyl 2-(benzylidene)hydrazino-1- azaazulene-3-carboxylates with dimethyl acetylenedicarboxylate

Article abstract of DOI:10.1246/bcsj.66.3735

Syntheses and cycloadditions of ethyl 2-(benzylidene)hydrazino-1- azaazulene-3-carboxylates were investigated. Condensations of ethyl 2- hydrazino-1-azaazulene-3-carboxylate with benzaldehyde and p-methoxy- benzaldehyde gave corresponding hydrazones in good yields. Reactions of ethyl 2-(benzylidene)hydrazino-1-azaazulene-3-carboxylate (2a) and ethyl 2-(p- methoxybenzylidene)hydrazino-1-azaazulene-3-carboxylate with dimethyl acetylenedicarboxylate gave novel 1:2-adducts, 4a,11,11a-triazaindeno[5,6- a]azulene derivatives and 2-methoxycarbonylimino-1-(2-pyrrolylmethyl)-1- azaazulene derivatives as major products. Reaction of 2a with electron deficient olefins (tetracyanoethylene, N-methylmaleimide) gave no cycloadduct but a cyclization product of 2a, 3-phenyl-1,2,3a-triazacyclopent[a]azulene- 9-carboxylate. The structures of the obtained compounds were analyzed by inspections of their physical and spectral data, and by single-crystal X-ray analyses of some of these compounds. The reaction mechanisms of these reactions are discussed.