Density Functional Theory Study of the Mechanism and Origins of Stereoselectivity in the Asymmetric Simmons–Smith Cyclopropanation with Charette Chiral Dioxaborolane Ligand - Liang Yong

Asymmetric Simmons–Smith reaction using Charette chiral dioxaborolane ligand is a widely applied method for the construction of enantiomerically enriched cyclopropanes. The detailed mechanism and the origins of stereoselectivity of this important reaction were investigated using density functional theory (DFT) calculations. Our computational studies suggest that, in the traditional Simmons–Smith reaction conditions, the monomeric iodomethylzinc allyloxide generated in situ from the allylic alcohol and the zinc reagent has a strong tendency to form a dimer or a tetramer. The tetramer can easily undergo an intramolecular cyclopropanation to give the racemic cyclopropane product. However, when a stoichiometric amount of Charette chiral dioxaborolane ligand is employed, monomeric iodomethylzinc allyloxide is converted into an energetically more stable four-coordinated chiral zinc/ligand complex. The chiral …