Diastereoselective Addition Reactions of Furyl Aldehydes Using Chiral Boronates as Auxiliary:  Application to the Enantioselective Synthesis of 2,3-Disubstituted Furyl Alcohols^†

The addition reactions of various nucleophiles to a furyl aldehyde bearing a chiral boronate at the C-3 position furnished chromatographically separable diastereomers. The R diastereoselection was more favorable when no additive was added. Surprisingly, when lithium alkoxides were selected as additives, the S diastereoselection is superior instead. Further transformation of C−B bonds to C−C bonds was achieved by using standard Suzuki coupling conditions to give optically active 2,3-disubstituted furyl alcohols.