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■ An Efficient Synthesis for Pyrimido[4',5':4,5]thieno[2,3-c]pyridazine Derivatives via Intramolecular Aza-Wittig Reaction-Heterocyclization Strategy

José M. Quintela,* Rafael Alvarez-Sarandés, M. Carmen Veiga, and Carlos Peinador

*Departamento de Química Fundamental Industrial, Facultad de Ciencias, Universidad de La Coruña, Campus de A Zapateria, s/n, E-15071, La Coruña, Spain

Abstract

A ready one-pot preparation for substituted pyrimidothienopyridazines is reported. Aza-Wittig reaction of iminophosphorane (3), derived from ethyl 5-amino-3,4-diphenylthieno[2,3-c]pyridazine-6-carboxylate (2), with isocyanates, followed by heterocyclization on addition of amines provided a novel synthetic route to the functionalized pyrimido[4’,5’;4,5]thieno[2,3-c]pyridazines (6). The guanidine-type intermediate compounds (5) derived from addition of amines to the carbodiimides (4) could be isolated and characterized, thus confirming the suggest reaction pathway.