Phosphazene-Catalyzed Cascade Esterification/Stereoselective Aza-Michael Addition of Chiral β-Trifluoromethyl-α,β-unsaturated N-Acylated Oxazolidin-2-ones

Upon treatment of chiral β-trifluoromethyl-α,β-unsaturated N-acylated oxazolidin-2-ones with a range of alcohols using phosphazene base as a catalyst, the unexpected cascade esterification/stereoselective aza-Michael addition was observed. The reactions proceeded with high diastereoselectivities (up to ≧ 99:1) to give a series of enantioenriched aza-Michael addition products in good to high yields. The structure and stereochemistry of the representative aza-Michael adduct were confirmed by X-ray analysis. The plausible mechanism was proposed on the basis of the experimental results. The synthetic transformations of chiral aza-Michael addition products were also demonstrated highlighting the synthetic application of the present work.