A CHALLENGING SYNTHETIC APPROACH TO PHOSPHONIUM YLIDE-BETAINES OF THEPYRIMIDINE SERIES

Adducts of the available ylide [GRAPHICS] with acylisocyanates and the ir thio analogues undergo facile cyclization, promoted by hydrogen chl oride in methanol, to give high yields of oxo-1,6-dihydropyrimidin-5-y l-triphenylphosphonium chlorides suitable to prepare several types of phosphonium ylide-betaines of the pyrimidine series, the structure of which was established by chemical transformations and X-ray diffractio n analysis. Despite the mesomeric character of these heterocyclic nucl eophilic agents, they are alkylated in a regioselective manner, which proves this approach to be important for the synthesis of non-phosphor ylated pyrimidine derivatives, which are otherwise difficult to obtain . (C) 1996 Elsevier Science Ltd