Synthesis of [1]benzothieno[3,2-d]pyrimidines substituted with electron donating substituents on the benzene ring

Various 2-fluorobenzonitriles were converted to the corresponding 3-amino[1]benzothiophenecarboxylic acid esters, which in turn were annulated with formamidine or various equivalents to produce the desired tricyclic benzothienopyrimidines. Various methoxy and nitro/amino substituents were placed on the phenyl ring, requiring several different strategies to prepare the desired benzothiophenes. Several different pyrimidone annulations were also required. The use of an electron rich 2-bromobenzonitrile in a four-step one-pot low temperature lithiation sequence to produce highly electron-rich amino[1]benzothiophenecarboxylate esters is also described. The synthesis of 7-amino-8-fluoro[1]benzothieno[3,2-d]pyrimid-4(3H)-one was relatively straightforward, but synthesis of the corresponding 7-amino-8-protio analogue proved to be very difficult, and required several approaches before a successful one was found.