Cycloadditions of extended dipoles: reaction of imidoylazimines with ketens

Abstract

Diphenyl-, phenylmethyl-, and dimethyl-keten undergo 2 + 2 cycloaddition to the CN bond of benzo[c]cinnoline N-(N-arylbenzimidoyl)imides (1) to give (β-lactams (2). On heating, these (β-lactams give either benzocinnoline and 1,2,4,4-tetrasubstituted imidazolin-5-ones (5) or triazolobenzocinnolines (8) depending on whether the substituents on the keten or imide stabilise heterolytic C–C or C–N bond cleavage of the β-lactam ring. p-Toluonitrile oxide also undergoes addition to the CN bond of (1) although the initial adduct is not isolable owing to its ready hydrolysis. No products resulting from other modes of cycloaddition to the extended dipoles (1) are observed with dimethyl acetylenedicarboxylate or reactive dienes.