Enantiodivergent Preparation of Optically Active Oxindoles Having a Stereogenic Quaternary Carbon Center at the C3 Position via the Lipase-Catalyzed Desymmetrization Protocol: Effective Use of 2-Furoates for Either Enzymatic Esterification or Hydrolysis

Both enantiomers of oxindoles 2a−h, having a stereogenic quaternary carbon center at the C3 position and a different N-protective group, were readily prepared by the lipase-catalyzed desymmetrization protocol. Thus, the transesterification of the prochiral diols 3a−h with 1-ethoxyvinyl 2-furoate 5 was catalyzed by Candida rugosa lipase to give (R)-(+)-2a−h (68−99% ee), in which the use of a mixed solvent, iPr2O (diisopropyl ether)−THF, was crucial. The same lipase also effected the enantioselective hydrolysis of the difuroates 4a−h in a mixture of iPr2O, THF, and H2O to provide the enantiomers (S)-(−)-2a−h (82−99% ee). The products 2 obtained by both methods were stable against racemization. These enzymatic desymmetrization reactions were also applicable for other typical symmetrical difuroates 12b and 15b to provide the racemization-resistant products 13b and 16b.