Oxazolidinones and Related Heterocycles as Chiral Auxiliaries/Evans and Post-Evans Auxiliaries

The application of optically active oxazolidinones and their sulfur-incorporating derivatives as chiral auxiliaries for the diastereoselective functionalization of carboxylic acids and related starting materials is described. Herein, seminal work and more recent contributions in this area covering the developments in the past 40 years are summarized. This review aims in demonstrating not only the broad and reliable, synthetic applicability of this auxiliary class but also the methodological impact on the area of diastereoselective chemistry in general. In the beginning, the preparation of the auxiliary by ex-chiral pool synthesis or enantioselective methods is reviewed. Following, the application of oxazolidinones and related derivatives in diastereoselective transformations is separately discussed for the electrophilic α-functionalization of enolates and aldol reactions. Herein, reported working models for explaining the stereochemical outcome of the transformations with respect to auxiliary structure and Lewis acid coordination are presented. In addition, the stereoselective transformation of α,β-unsaturated acyl-oxazolidinones by either conjugate additions or pericyclic reactions is summarized in detail. The discussion is extended toward the diastereoselective, electrophilic functionalization of vinyl-, alkynyl-, or allenyl-oxazolidinones extending the scope of the auxiliary towards the transformation of carbonyl compounds. Finally, this review is complemented by examples of the employment of oxazolidinones for the stereoselective reaction of auxiliary-bound carbenium ions or carbanions. Throughout this review, references for the application of this highly useful class of chiral auxiliary in the context of natural product synthesis are provided.