Stereoselective Conjugate Addition of Mixed Organoaluminum Reagents to α,β-Unsaturated<i>N</i>-Acyloxazolidinones Derived from Carbohydrates
作者:Horst Kunz、Stephan Elzner、Steffen Maas、Stefan Engel
DOI:10.1055/s-2004-831173
日期:——
β-branched carboxylic acid derivatives was accomplished by conjugateaddition of mixed organoaluminum reagents to chiral α,β-unsaturated N-acyloxazolidinones. Mixed organoaluminum reagentswere generated in situ by transmetalation of Grignard or organolithium compounds with methylaluminum dichloride. Efficient stereocontrol was achieved using different bicyclic glycosamine-derived oxazolidinones, yielding
β-Branched α-Halo Carboxylic Acid Derivatives via Stereoselective 1,4 Addition of Dialkylaluminum Chlorides to α,β-Unsaturated <i>N</i>-Acyloxazolidinones
The stereoselective synthesis of beta-branched alpha-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 alpha,beta-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 beta-branched alpha-halo carboxylic acids can be stereoselectively synthesized by this method. However, the reactions of beta-aryl alpha,beta-unsaturated N-acyloxazolidinones show the highest diastereoselectivity and give one out of four possible diastereomers in high excess.