σ-Bond Migration Assisted Decarboxylative Activation of Vinylene Carbonate in Rh-Catalyzed 4+2 Annulation: A Theoretical Study

As a C2 synthon, vinylene carbonate has been used instead of acetylene in transition-metal catalyzed-coupling reactions. In this study, the mechanism of the vinylene carbonate activation mode for the Rh(III)-catalyzed 4 + 2 annulation of benzamide and vinylene carbonate reaction is proposed, and it was investigated by DFT with the M06 density functional. The computational results show that the proposed reaction pathway, which includes the insertion of vinylene carbonate into an Rh-C bond, decarboxylation of the seven-membered rhodacycle intermediate, protonation of the ketonate rhodium intermediate, deprotonation of the benzamide, and catalyst regeneration, is the most favorable pathway. The 1,2-rhodium migration process can assist decarboxylative activation of vinylene carbonate, which is the rate-determining step in the catalytic cycle. The IRC calculation clearly revealed a quasi-synchronized process to directly afford a cyclic ketonate rhodium intermediate by the release of carbon dioxide.