The readily available 4-mercapto-6-methyl-2-phenyl-5-acetylpyrimidine (1) was alkylated with a variety of activated halomethylene compounds to give the corresponding thieno [2,3-d] pyrimidine derivatives 3a-h via the intermediate alkylmercaptopyrimidine derivatives 2b-h. The biological activity of the new compounds was screened against several strains of bacteria.