A series of 1-glycosyl-2-glycosylthiopyrimidine (4), annelated pyrimidine derivatives. pyrazolo[3.4-d]pyrimidine (8), ditetrazolo[1,5-a;1',5'-c]pyrimidine (9), 2,9a,10-triazaanthracene (12), thieno[2,3-d]pyrimidine (14), 9-thia-1,3,5,7-tetraazafluorene-8-one (15), 7-oxa-9-thia-1,3,5-triazafluorene-8-one (16). 5-oxa-9-thia-1,3-diazafluorene (21a and 21b) derivatives have been synthesized via a sequence of heterocyclization reactions of suitably functionalized 6-[5-(4-bromophenyl)oxazol-4-yl]-1,2,3,4-ten-ahydro-2-thioxo-4-oxopyrimidine-S-carboninile (2) with different electrophiles and nucleophiles. The new compounds were prepared with the objective to study their pharmacological properties.