Biocatalytic approaches to both enantiomers of (2R*,3S*)-2-allyloxy-3,4,5,6-tetrahydro-2H-pyran-3-ol

Both enantiomers of (2R*,3S*)-2-allyloxy-3,4,5,6-tetrahydro-2H-pyran-3-ol, a precursor of chiral auxiliary for asymmetric addition of organometallics, and its analog, (2S,3S)-2-ethoxy-3,4,5,6-tetrahydro-2H-pyran-3-ol were prepared by biocatalytic optical resolutions. Lipase-catalyzed enantioselective acetylation of the racemate in organic solvent worked well with a high enantioseleclivity. Pseudomonas cepacia lipase was most effective (E = 11-17) for the kinetic resolution. Under the optimized condition, the products, (2R,3S)-2-allyloxy-3,4,5,6-tetrahydro-2H-pyran-3-ol and (2S,3S)-2-ethoxy analog with more than 97% e.e. were obtained in 31-45% yield with 52-62% conversion. The enantiomer, (2S,3R)-2-allyloxy compound was secured by two ways. The repetition of the lipase-catalyzed acetylation on partially enantiomerically enriched substrate afforded the acetate with a high e.e. (97%). A newly developed double resolution procedure in one-pot reaction was also successful. In this case, the apparent E value via two steps became as high as 71.