An unusual Michael addition of 3,3-dimethoxypropanenitrile to 2-aryl acrylates: A convenient route to 4-unsubstituted 5,6-dihydropyrido[2,3-d] pyrimidines

(Chemical Equation Presented) An unusual Michael addition between 2-aryl-substituted acrylates and 3,3-dimethoxypropanenitrile which leads, depending on the reaction temperature (60 or -78 °C, respectively), to a 4-methoxymethylene-substituted 4-cyanobutyric ester or to a 4-dimethoxymethyl 4-cyanobutyric ester is described. These compounds can be subsequently converted to 4-unsubstituted pyrido[2,3-d]-pyrimidines upon treatment with a guanidine system under microwave irradiation.