A facile one-pot regioselective synthesis of [1,2,4]triazolo[4,3-a]5(1H)-pyrimidinones via tandem Japp-Klingemann, smiles rearrangement, and cyclization reactions

Coupling of active [(4-oxo-6-phenyl-3H-pyrimidin-2-yl)thio]methine compounds (3) with diazotized anilines in the presence of base gave [1,2,4]triazolo[4,3-a]pyrimidines (7). The latter products were also obtained by reactions of hydrazonoyl chlorides (10) with either 6-phenyl-2-thiouracil (1) or the 2-methylthio derivative 9. The mechanisms and the regiochemistry of the reactions studied are discussed. (C) 2002 Wiley Periodicals, Inc.