Asymmetric Silyl Transfer by Transition-Metal-Free NHC Catalysis

Significance

Following their previous report regarding the C-B bond-formation reaction pro­moted by NHC (K.-S. Lee, A. R. Zhugralin, A. H. Hoveyda J. Am. Chem. Soc. 2009, 131, 7253), the authors report an asymmetric C-Si bond-formation reaction using chiral NHC in aqueous medium. By subjecting the imidazolinium salt and silyl boronic ester in the presence of a stoichiometric base, the complex A, which can undergo a silyl transfer reaction, could be observed by ^¹¹B NMR spectroscopy. The presented method shows high selectivity for the C-Si bond formation with good to excellent enantioselectivity. Various substrate classes are tolerated under the reaction conditions, including cyclic and acyclic enones, α,β-unsaturated esters, and enals.