Mechanism and Origins of Enantioselectivity of Rhodium‐Catalyzed [4+3] Annulation of Benzosilacyclobutenes with 7‐Oxabenzonorbornadienes

Abstract

ABSTRACT Rhodium‐catalyzed asymmetric [4+3] annulation of benzosilacyclobutenes with 7‐oxabenzonorbornadienes provides an efficient route to enantioenriched seven‐membered sila‐heterocycles. In this study, density functional theory calculations were performed to elucidate the reaction mechanism and the origins of the enantioselectivity. The catalytic cycle is initiated by C─Si oxidative addition to generate the Rh(III) metallacyclic intermediate. However, the subsequent migratory insertion followed by the β‐O elimination pathway was found to be kinetically infeasible. Instead, the computations reveal that the Rh(III) metallacyclic intermediate undergoes Si─Cl reductive elimination to generate the Rh(I)‐aryl species, from which the annulation proceeds through migratory insertion, β‐O elimination, and σ‐bond metathesis. The C─Si oxidative addition step constitutes the rate‐determining step, whereas the migratory insertion step is responsible for controlling the enantioselectivity. Structural and distortion/interaction analyses demonstrate that the stereochemical outcome is predominantly governed by the steric repulsion between the chiral ligand and the 7‐oxabenzonorbornadiene substrate.