Baker's yeast-mediated approach to (-)-cis- and (+)-trans-Aerangis lactones.

The first enantioselective synthesis of natural (-)-cis-Aerangis lactone (-)-1a and its (+)-trans-diastereoisomer (+)-lb is described. The key steps in the synthesis are: (i) the enantiospecific and 100% diastereoselective baker's yeast reduction of 1,4-keto acid 2, to afford enantiopure trans- cognac lactone (+)-10; (ii) the regioselective PPL-mediated hydrolysis of the primary acetate moiety of diacetate (+)-(3S,4R)-3, obtained from (+)-10. Chain elongation by one carbon atom via cyanide substitution, and inversion of the configuration of C(5) in nitrile derivative (+)-21a are also required to complete the synthetic route to (-)-1a.