Asymmetric umpolung α-arylation and α-azidation of Evans’ propionyloxazolidin-2-one

Umpolung of enolates is a valuable strategic alternative to classical chemistry. It allows an orthogonal way of planning synthesis and opens exciting opportunities for developing novel reactions. Recently, we reported that ketones can form discrete electrophilic enolonium species under mild conditions through the influence of a hypervalent iodine reagent. We now report that also imides are able to form useful elononium species. We have applied this finding to the asymmetric reaction of chiral Evans’ acyl-oxazolidin-2-ones with azide and aromatic nucleophiles. The reaction affords the products in yields ranging from 70 to 90% as single diastereoisomers. The azido products may be used as intermediates for the preparation of unnatural amino acids.