Facile Entries for Regioselective Synthe sis of [1,2,4]Triazolo- [4,3-a]pyrimidin-5(1H)-ones from 2-Thiouracil

A.S. Shawali^a,*, I.M. Abbas^a and A.M. Mahran^b

^a Department of Chemistry, Faculty of Science, University of Cairo,Giza,Egypt ^b National Research Centre, Dokki, Giza, Egypt

 Three new alternative synthetic strategies  based on reactions of hydrazonoyl halides 3 with 2-methylthiouracil 2 and treatment of either 2 -pyrimidinyl thiohydrazonates 8 or the diazonium coupling products of active (pyrimidin-2-ylthio)methylene compounds 12 with sodium ethoxide in ethanol are described for the title compounds. The mechanisms and regiochemistry of the studied reactions are discussed.

Keywords: Heterocycles, Hydrazones, Rearrangement, Synthetic methods, 1,2,4-Triazolo-pyrimidine