I 2 -DMSO-Mediated Construction of 2,3- and 2,4-Disubstituted Pyrimido[1,2- b ]indazole Skeletons.

An efficient synthetic method for constructing 2,3- and 2,4-disubstituted pyrimidio[1,2- b ]indazole skeletons through I 2 -DMSO-mediated and substrate-controlled regioselective [4 + 2] cyclization is reported. The reaction conditions are mild, its operation is simple, and the substrate scope is wide. More than 60 pyrimidio[1,2- b ]indazole derivatives have been synthesized, providing a new methodology for constructing related molecules and potentially enriching bioactive-molecule libraries.