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

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.