Cyclization of 2-furan-2-yl-4-mercapto-6-methylpyrimidine-5-carbonitrile 1 with ethyl chloroacetate gave o-aminoester thienopyrimidine derivative 3, which was reacted with a variety of reagents to give a series of novel thienopyrimidines including tetrazolyl thienopyrimidine, pyrrolylthienopyrimidine, pyrimidothienotriazine, and thienodipyrimidines. Some of the synthesized compounds were tested for their antibacterial activities against Gram-positive and Gram-negative bacteria.