Cyclocondensation of oxoketene dithioacetals with 3-aminopyrazoles: a facile highly regioselective general route to substituted and fused pyrazolo ]pyrimidines
3-amino-5-methylthio-4-phenylpyrazole (1b) withα-oxoketene dithioacetals (2a-j derived from acyclic active methylene ketones affords 5-methylthio-6,7-substituted pyrazolo[1,5-a]pyrimidines (3a-J) exclusively. The reaction was found to be equally successful for the synthesis of 7-styryl,7-(4-aryl-1,3-butadienyl) and 7-(6-aryl-1,3,5-hexatrienyl)pyrazolopyrimidines (7a-f) from the respective enoylketene dithioacetals (6a-f)