Synthesis of 5,6-dihydrothieno(and furo)pyrimidines bearing an active methine group at the 4-position

The reactions of 2-benzamido-4,5-dihydro-3-thiophene(and -3-furan)carbonitriles (1a-c and 4a-c) with ethyl acetoacetate in the presence of tin(IV) chloride and triethylamine provided the corresponding ethyl 2-(5,6-dihydro-2-phenylthieno(and furo)[2,3-d]pyrimidin-4-yl)-3-oxobutanoates (2a-c and 9a-c). Similarly, compounds 1a-c and 4a-c reacted with dialkyl malonates to give the corresponding dialkyl(5,6-dihydro-2-phenylthieno(and furo)[2,3-d]pyrimidin-4-yl)propanedioates (5a-c, 6a-c, 10a-c and 11a-c).