One-Pot Three-Step Synthesis of Pyrazinothienopyrimidines Using Tandem Aza-Wittig/Electrocyclic Ring Closure

A facile and efficient one-pot procedure for the preparation of pyrazino[3',2':4,5]thieno[3,2-d]pyrimidines following a tandem aza-Wittig/electrocyclic ring closure strategy is described. The one-pot, three-step reaction between 3-amino-2-formylthieno[2,3b]pyrazine, primary amines, dichlorotriphenylphosphine and heterocumulenes, proceeded effectively and the yields of the products were higher than in the stepwise process. The products can also be prepared directly by a one-pot, two-step reaction using the same aldehyde, dichlorotriphenylphosphine and isocyanates. The advantages of the present method are easily accessible starting materials, experimental simplicity of the one-pot procedure, and good yields.