Carbon Acid Induced Mukaiyama Aldol Type Reaction of Sterically Hindered Ketones

1,1,3,3-Tetrakis(trifluoromethanesulfonyl)propane (Tf₂CHCH₂CHTf₂) is one of the most effective Brønsted acid precatalysts for the Mukaiyama aldol type reactions of sterically hindered ketones. By using Tf₂CHCH₂CHTf₂ in a range from 0.5 to 2.0 mol %, the vinylogous Mukaiyama aldol reaction of α-substituted cyclohexanones with 2-silyloxyfurans smoothly proceeded to give the aldol products in excellent yield without the loss of diastereoselectivity. Under similar conditions, acyclic ketene silyl acetals also performed as nice nucleophiles toward sterically hindered ketones. These findings suggest that Tf₂CHCH₂CHTf₂ induced Mukaiyama aldol type reactions can overcome the steric hindrance between reaction sites.