Asymmetric [2 + 2] cycloaddition of ketene with aldehydes catalysed by chiral bissulfonamide–trialkylaluminium complexes

Abstract
Asymmetric [2 + 2] cycloaddition of ketene with the aldehydes 1a–g, catalysed by 10 mol% of C2-symmetric bissulfonamide 2a–c–R3Al complexes afforded optically active 4-substituted oxetan-2-ones 3a–g in up to 74% enantiomeric excess.