Cascade Reaction by Chemo‐ and Biocatalytic Approaches to Obtain Chiral Hydroxy Ketones and anti 1,3‐Diols

A chemo‐ and biocatalytic cascade approach was applied for the stereoselective synthesis of hydroxy ketones and the corresponding 1,3‐diols. A new class of tridentate N,N,O ligands was used with copper(II) complexes for the asymmetric β‐borylation of α,β‐unsaturated compounds. The complex containing ligand L5 emerged as the best performer, and it gave the organoborane derivatives with good ee values. The corresponding keto–alcohol compounds were then bioreduced by yeasts. The biotransformation set up with Rhodotorula rubra allowed (R)‐keto–alcohols and (S,S)‐diols to be obtained with up to 99 % ee and up to 99 % de in favor of the anti enantiomers.