New Efficient Route to Dissymmetric 2,4-Di(het)aryl-pyrido[3,2-d]pyrimidines via Regioselective Cross-Coupling Reactions

The first access to dissymmetric 2,4-di(het)aryl-pyrido[3,2-d]pyrimidines III is reported. Two mild alternative routes led to the rarely targeted compounds from 2,4-dichloro- and 2-chloro-4-isopropylsulfanyl-pyrido[3,2-d]pyrimidine by two successive palladium-catalyzed reactions involving an original regioselective chlorine discrimination. Alternatively, type III compounds were elaborated from 2 by C-2 chlorine further displacement of the C-4 isopropylsulfanyl group, which acted as a temporary C-4 protecting group. These results open the way to innovative synthesis strategies of various bis-functionalized pyrimidine series.