Borane-Catalyzed Divergent Hydrogenative and Silylative Reduction of Quinolinium Salts

A B(C6F5)3-catalyzed chemoselective reduction of quinolinium salts was developed. This method afforded two distinct products in good to high yields by solvent modulation. In 1,4-dioxane, the reaction proceeds selectively to silylative reduction products, whereas in 1,2-dichloroethane, it gives direct hydrogenative reduction products. The selectivity may depend on the stability of silylium cations, which determines whether the key enamine intermediate undergoes silylation or protonation to form different products.