Stereoselective synthesis of ( E )-halomethylidene[1,3]thiazolo[3,2- a ]thieno[3,2- e ]pyrimidinium and analogous [1,3]oxazolo[3,2- a ]thieno[3,2- e ]pyrimidinium halides starting from 3- N -substituted 2-propargylthio(oxy)thieno[2,3- d ]pyrimidin-4-ones

A convenient procedure for the stereoselective synthesis of [1,3]thiazolo[3,2- a ]thieno[3,2- e ]pyrimidinium halides and analogous [1,3]oxazolo[3,2- a ]thieno[3,2- e ]pyrimidinium halides 5 and 6 is reported. 2-Propargylthio-3- R -thieno[2,3- d ]pyrimidin-4-ones and 2-propargyloxy-3- R -thieno[2,3- d ]pyrimidin-4-ones were treated with bromine or iodine in AcOH to afford ( E )-halomethylidene[1,3]thiazolo[3,2- a ]thieno[3,2- e ]pyrimidinium and ( E )-halomethylidene-[1,3]oxazolo[3,2- a ]thieno[3,2- e ]pyrimidinium halides, respectively.