β-Branched α-Halo Carboxylic Acid Derivatives via Stereoselective 1,4 Addition of Dialkylaluminum Chlorides to α,β-Unsaturated N-Acyloxazolidinones

The stereoselective synthesis of β-branched α-halo carboxylic acids containing two newly formed chiral centers is accomplished by a reaction cascade consisting of the 1,4 addition of dialkylaluminum chlorides to α,β-unsaturated N -acyloxazolidinones and subsequent reaction of the intermediate aluminum enolates with N -halosuccinimide. The most efficient stereocontrol in these tandem processes has been achieved with oxazolidinones derived from glucosamine. Not only aryl substituted but also purely aliphatic β-branched α-halo carboxylic acids can be stereoselectively synthesized by this method. However, the reactions of β-aryl α,β-unsaturated N -acyloxazolidinones show the highest diastereoselectivity and give one out of four possible diastereomers in high excess.