Biocatalysis is recognized as a useful tool for organic synthesis, especially for the asymmetric synthesis of natural products. As part of our efforts to synthesize versatile chiral building blocks by adopting biocatalysis, we developed the lipase-catalyzed desymmetrization of the meso-glycol 1 and the meso-diacetate 2 to afford both enantiomers of the ketol acetate 4 as an optically pure state, respectively. The desymmetrization of the meso-glycol 5 was also achieved to give the monoacetate (-)-6, which was led in three steps to the decalin (+)-19. Enantiomerization of (+)-19 was readily accomplished to give (-)-19. On the other hand, baker's yeast reduction of the β-keto ester 7 proceeded in a highly enantioselective manner and furnished the homochiral piperidone (-)-8 in good yield. The enantiomer (+)-8 was obtained by the lipase-mediated optical resolution of (±)-8. Thus, we achieved highly efficient synthesis of both enantiomers of chiral building blocks 4, 6, 8. The versatility of 4, 6 and 8 for natural product synthesis was demonstrated by the first total synthesis of(-)-cassine (11), (+)-spectaline (12), (-)-indolizidine 235B' and the formal synthesis of (-)-dihydropinidine, (-)-indolizidine 207A, 209B, (-)-polygodial, (-)-warburganal, (-)-drimenin, and prosopinie, respectively.
