Reductive Carbocyclization of Homoallylic Alcohols to syn-Cyclobutanes by a Boron-Catalyzed Dual Ring-Closing Pathway

The organoborane-catalyzed reductive carbocyclization of homoallylic alcohols has been developed by using hydrosilanes as reducing reagents to provide a range of 1,2-disubstituted arylcyclobutanes. The reaction proceeds in a cis-selective manner with high efficiency under mild conditions. Mechanistic studies, including deuterium scrambling and Hammett studies, and DFT calculations, suggest a dual ring-closing pathway.