New efficient synthesis of pyrimido[1,6-c]quinazolin-4-ones by a Biginelli 3CC/Staudinger/aza-Wittig sequence

Abstract Dihydropyrimidinone azides 1 , obtained from trimethylsilyl chloride-catalyzed Biginelli reaction of 2-azidobenzaldehyde, ethyl acetoacetate, and urea (or thiourea) at room temperature, reacted with triphenylphosphine to give iminophosphorane 2 . A tandem aza-Wittig reaction of iminophosphorane 2 with isocyanate, acyl chloride or CS 2 in the presence of K 2 CO 3 or NEt 3 generated pyrimido[1,6- c ]quinazolin-4-ones 4 , 6 or 8 in moderate to good yield.