Extended dipolar cycloadditions

Abstract

Whilst the simple azomethine imine (5) undergoes the expected 1,3-dipolar cycloaddition to acetylenic esters, the extended azomethine imines (1) undergo 1,5-rather than 1,3-dipolar cycloaddition to give benzo[c][1,2,5]-triazepino[1,2-a]cinnolines (2), possibly by a stepwise mechanism 2-Alkyl-2λ⁵σ³-naphtho[1,8-de]triazines (12) and 2λ⁴σ²-naphtho[1,8-cd]thiadiazine (18) undergo 1,11-dipolar [12π+ 2π] cycloaddition to acetylenic esters to give the peri-bridged acenaphthylenes (14) and (19), after spontaneous dehydrogenation. It is suggested that these and other reactions in the literature illustrate the potential generality of extended dipolar cycloadditions.