An Efficient Semipinacol Rearrangement toward α,β-Unsaturated Ketones via Lewis Acid and Base Synergistic Catalysis.

An efficient semipinacol rearrangement undergoing 1,2-migration toward α,β-unsaturated ketones via a synergistic Lewis acid and base cocatalysis strategy is developed, providing a direct and efficient access to diverse and valuable 1,4-dicarbonyl compounds bearing α-stereocenters with high atom economy, in which the catalytic base has played an essential role for the expected reactivity. Benefited from this method, a series of semipinacol rearrangement that otherwise could not be realized from previous reports could be successfully achieved, including the 1,2-aryl migration and 1,2-cycloalkyl migration overcoming the limitation of strained ring and rearomatization, thus bringing more opportunity for the practical application of related 1,4-dicarbonyl compounds. Classical substrate scope studies disclose the regularity on migration sequence. Further mechanistic studies confirm the 1,2-migration mechanism and give comprehensive insights for this transformation.