Application of the aza-Wittig reaction to the synthesis of pyrazinothienotriazolopyrimidinones: a new tetracyclic ring system

A simple one-pot and efficient method is described for the synthesis of pyrazinothienopyrimidines 6 by domino processes involving aza-Wittig/intermolecular nucleophilic addition/intramolecular cyclization. A tandem aza-Wittig reaction of phosphazenes 7, derived from 6, with heterocumulenes (isocyanates, carbon disulfide or carbon dioxide) generates the pyrazinothienotriazolopyrimidinones 9, 11 and 12, respectively. Pyrazino[2′,3′:4,5]thieno[3,2-d]-1,2,4-triazolo[1,5-a]pyrimidin-4(3H)-ones 15 and bis(pyrazinothienotriazolopyrimidinones) 17 were synthesized by the intermolecular aza-Wittig reaction of phosphazenes 7 with acyl chlorides or α,ω-dichlorides followed by heterocyclization via imidoyl chloride intermediate 16. Further S-alkylation of 11 and reaction of 6 with phosgeniminium chloride produce 2-alkylthio- and 2-N,N-dimethylaminopyrazinothienotriazolopyrimidinones 13 and 19, respectively.