REACTIONS OF 5-CYANO-1,4-DIPHENYLPYRIDAZINO[4,5-A]INDOLIZINES WITH DIMETHYL ACETYLENEDICARBOXYLATE - REGIOSELECTIVE FORMATION OF 1 2 MICHAEL TYPE ADDUCTS/

Reactions of 5-cyano-1,4-diphenylpyridazino[4,5-a]indolizines with dim ethyl acetylenedicarboxylate afforded the 1:2 adducts regioselectively and, unexpectedly, in a Michael fashion rather than in a 1,3-dipolar manner. The structure of the products was established by X-ray crystal lography. Regiospecific formation of the observed product 3 can be exp lained by the higher nucleophilicity of the nitrogen at the 2 position than at the 3 position of the 5-cyano-1,4-di-phenylpyridazino[4,5-a]i ndolizine 1 owing to the contribution of a resonance structure 5 to th e hybrid. This favors two successive Michael additions to two equivale nts of dimethyl acetylenedicarboxylate affording the observed 1:2 addu cts 3.