The first enantioselective synthesis of natural (−)-cis-Aerangis lactone (−)-1a and its (+)-trans- diastereoisomer (+)-1b 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. ...