BETA-BRANCHED ALPHA-HALO CARBOXYLIC-ACID DERIVATIVES VIA STEREOSELECTIVE 1,4-ADDITION OF DIALKYLALUMINUM CHLORIDES TO ALPHA,BETA-UNSATURATED N-ACYLOXAZOLIDINONES

The stereoselective synthesis of beta-branched alpha-halo carboxylic a cids containing two newly formed chiral centers is accomplished by a r eaction cascade consisting of the 1,4 addition of dialkylaluminum chlo rides to alpha,beta-unsaturated N-acyloxazolidinones and subsequent re action of the intermediate aluminum enolates with N-halosuccinimide. T he most efficient stereocontrol in these tandem processes has been ach ieved with oxazolidinones derived from glucosamine. Not only aryl subs tituted but also purely aliphatic beta-branched alpha-halo carboxylic acids can be stereoselectively synthesized by this method. However, th e reactions of beta-aryl alpha,beta-unsaturated N-acyloxazolidinones s how the highest diastereoselectivity and give one out of four possible diastereomers in high excess.