Three successive and regiocontroled palladium cross-coupling reactions to easily synthesize novel series of 2,4,6-tris(het)aryl pyrido[1′,2′:1,5]pyrazolo[3,4-d]pyrimidines†
The first access to tris(het)arylated pyrido[1′,2′:1,5]pyrazolo[3,4-d]pyrimidine derivatives is reported. The series were generated from 4-chloroaminopyridinium, which afforded the key intermediate bearing three leaving groups, i.e. a C-2 methylsulfanyl, a lactame carbonyl group in C-4 and a chlorine atom in C-6. The regioselective reactions led to the tris(het)aryl derivatives with satisfying to high yields. The three successive cross-coupling reactions occurred first in C-6 by the displacement of chlorine, next in C-4 position by a sequential Pd-catalyzed phosphonium coupling and finally in C-2 under a Pd/Cu-catalyzed desulfitative cross-coupling reaction. The optimization and scope of each reaction are discussed and the original compounds characterized.