Highly diastereoselective domino synthesis of 6-spirosubstituted pyrido[2,3-d]pyrimidine derivatives in water.

A highly diastereoselective domino reaction of 2,6-diaminopyrimidine-4-one with structurally diverse aryl aldehydes and various barbituric acids in water under microwave irradiation is described. The products are 6-spiro-substituted pyrido[2,3-d]pyrimidines with high diastereoselectivities (up to 99: 1) in which the major diastereomer bears a cis relationship between substituents at the 5- and 7-positions. Furthermore, the mechanism for diastereoselectivity was confirmed by DFT (B3LYP) calculations.