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. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:136–140, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10008