Stereoselective α-Acylvinyl Additions Using Lewis Acids

Significance

Silyloxyallenes, synthesized from acylsilanes via a [1,2]-Brook rearrangement, perform stereoselective α -acylvinyl additions to aldehydes when catalyzed by scandium(III). Excellent yields and control over E:Z geometry is seen, with the Z-isomer favored. A variety of alkyl and aryl aldehydes react with siloxyallenes containing diverse β-substituents. Although attempts to control the enantioselectivity of the acyl addition with a chiral allene were unsuccessful, use of a chiral chromium Lewis acid with racemic silyloxyallene resulted in 92% ee.