Spirocyclisation reactions of diethyl pyridazine-4,5-dicarboxylate with 1,3-binucleophiles

Abstract

Treatment of diethyl pyridazine-4,5-dicarboxylate (1) and diethyl 3,6-dimethylpyridazine-4,5-dicarboxylate (2) with 1,3-diphenylguanidine in the presence of sodium hydride, gave ethyl 4-oxo-1-phenyl-2-(phenylimino)-l,3,7,8-tetra-azaspiro[4,5]deca-6,9-diene-10-carboxylate (11) and its 6,9-dimethyl derivative (13), respectively. The influence of the nature of the substituents on the spirocyclisation reaction was investigated by studying the reactivity of the esters (3)–(6) towards the same reagents. The ester (1) condensed with diethyl succinate to yield a small amount of diethyl 5,8-dihydroxyphthalazine-6,7-dicarboxylate (18), but reacted with diethyl glutarate and diethyl acetonedicarboxylate to give the diazaspirodecadienes (19) and (20), respectively.