Abstract: 2-Methylsulphanyl-5-aminothiazole-4-carboxamide 1 has been used as a convenient precursor for the synthesis of new thiazolo [4, 5-e][1, 2, 4-triazolo][4, 3-c] pyrimidines 5 and the corresponding tetrazolo analogue 7. A mesoionic isomer 8 seems to exist along with 7. Interesting heteroarylthiazolo pyrimidine motifs have also been prepared via suitably substituted thiazolo [5, 4-d] pyrimidines.