Diversity-oriented synthesis of imidazo[2,1-a]isoquinolines

Herein, we report an efficient and practical strategy for the synthesis of five types of imidazo[2,1-a] isoquinolines via Cp*Rh-III-catalyzed [4+2] annulation of 2-arylimidazoles and alpha-diazoketoesters, whose structural and substituted diversity at 5- or 6-position can be precisely controlled by the alpha-diazoketoester coupling partners. Compared with previous reports, in this study, we merged two attractive C-C cleavage strategies (retro-Claisen and decarboxylation) into the classical C-H functionalization/condensation process by choosing appropriate ester groups (-COOEt, -COOtBu or -COOiPr) or inexpensive additives (HOAc or KOAc). Moreover, the synthetic efficacies of thesemethods were demonstrated by the concise synthesis of several bioactive compounds and the late-stage modification of representative drugs.