Stereoselective Access to Silicon-Stereogenic Silacycles via the Carbene-Catalyzed Desymmetric Benzoin Reaction of Siladials

The catalytic asymmetric synthesis of silicon-stereogenic organosilicon compounds has been a long-standing challenging task and was recently accomplished through a handful of transition-metal-catalyzed approaches. Herein we report an organocatalytic desymmetrization strategy for constructing optically active silicon-stereogenic silacycles. In the presence of a chiral N-heterocyclic carbene (NHC) catalyst, two identical formyl groups on the tetrasubstituted silanes are successfully discriminated to undergo stereoselective intramolecular benzoin reactions, affording enantioenriched dibenzo­[b,f]­silepin-10-ones featuring carbon- and silicon-stereogenic centers at the 1,4-positions, respectively. This catalytic process can be readily expanded to the gram scale, and the products can be further converted to other valuable molecules. DFT calculations were also conducted to unveil the reaction mechanism and the origins of the stereoselectivities.