Asymmetric [2 + 2] cycloaddition of ketene with aldehydes catalysed by Me3Al complexes of axially chiral 1,1′-binaphthalene-2,2′-diol derivatives

Abstract

Asymmetric [2 + 2] cycloaddition of ketene 1 with the aldehydes 2a–f, catalysed by axially chiral Lewis acids 3a–c afforded optically active 4-substituted oxetan-2-ones 4a–f in up to 56% enantiomeric excess (e.e.); the stereoselectivity of the reaction depended on the structure of the chiral Lewis acids and of the aldehydes, the order of addition of compounds 1 and 2 and on the solvents employed.