1,3-Dipolar cycloaddition of azolium dicyanomethylides

Abstract

1,3-Dipolar cycloaddition of azolium N-dicyanomethylides, which have an azomethine ylide structure, to acetylenic dipolarophiles affords azolopyridine derivatives. The initial cycloadduct has been isolated for the first time. Using unsymmetrical dipolarophiles, only one of the two possible regioisomers has been obtained. The orientation problem has been approached theoretically by a second-order perturbational treatment, which also gives good results in the case of the reaction of an azomethine imine, 1-ethylbenzotriazolium 3-dicyanomethylide.