One-Pot Synthesis of Pyrazinothienopyrimidinones

Significance

A three-step synthesis of pyrazino[2′,3′:4,5]thieno[3,2-d]pyrimidines is reported. The thiophene ring annulation to the pyrazine is achieved in very good yields by treatment of 3-benzenesulfonylpyrazine-2-carbonitrile with 2-mercaptoacetate. The pyrimidinone ring closure is effected via an aza-Wittig/heterocumulene-mediated annulation strategy. The products are formed in very good yields for R¹ = amine substituents, while corresponding ether substituents give lower yields. The reaction proceeds via a carbodiimide as was verified by direct synthesis of the proposed intermediate and conversion into the products under the given conditions.