Oxyallyl Cation Capture via Electrophilic Deborylation of Organoboronates: Access to α,α'-Substituted Cyclic Ketones

An umpolung strategy to synthesize alpha,alpha'-substituted cyclic ketones through the nucleophilic addition of organoboronates to alpha-hydroxyl silyl enol ethers is described. The reaction proceeds via the trapping of in situ generated oxyallyl cations via the electrophilic deborylation of C(sp(2)) and C(sp) borates. This efficient and straightforward method provides direct access to alpha-substituted silyl enol ethers in high yield with complete regioselectivity. Desilylation in a one-pot procedure provides the corresponding alpha,alpha'-disubstituted ketones with high diastereoselectivity.