Selective Synthesis of Bis(thieno[2,3-d]pyrimidin-4(3H)-ones)

The iminophosphorane 2 was obtained using ethyl 2-amino-4-trifluoromethyl-5-methyl-thiophene-3-carboxylate (1) as starting materials. Further aza-Wittig reactions of iminophosphorane 2 with aromatic isocyanate and primary diamine produced 2,2'-disubstituted bis(thieno[2,3-d]pyrimidin-4(3H)-ones) 3 in the presence of catalytic amounts of potassium carbonate in 70%similar to 87% yields. Aza-Wittig reactions of iminophosphorane 2 with alkyl isocyanate and primary diamine produced 3,3'-disubstituted bis(thieno[2,3-d]pyrimidin-4(3H)-ones) 4 in 38%similar to 57% yields. H-1 NMR of compound 3 revealed the exclusive selectivity of these ring closures toward the 2,2'-disubstituted position of pyrimidine moiety, and H-1 NMR of compound 4 revealed the exclusive selectivity of these ring closures toward the 3,3'-disubstituted position of pyrimidine moiety. The reaction mechanism was also proposed for the regioselectivity.