Enantio- and Diastereoselective 1,2-Additions to α-Ketoesters with Diborylmethane and Substituted 1,1-Diborylalkanes

The catalytic enantioselective synthesis of boronate‐substituted tertiary alcohols through additions of diborylmethane and substituted 1,1‐diborylalkanes to α‐ketoesters is reported. The reactions are catalyzed by readily available chiral phosphine/copper(I) complexes and produce β‐hydroxyboronates containing up to two contiguous stereogenic centers in up to 99:1 e.r. and greater than 20:1 d.r. The utility of the organoboron products is demonstrated through several chemoselective functionalizations. Evidence indicates the reactions occur via an enantioenriched α‐boryl‐copper‐alkyl intermediate. Catalytic enantioselective synthesis of boronate‐substituted tertiary alcohols is possible through the title reaction. The reactions are catalyzed by chiral phosphine/copper(I) complexes and produce β‐hydroxyboronates containing up to two contiguous stereogenic centers. The utility of the organoboron products is demonstrated through several chemoselective functionalizations. pin=pinacolato, TMS=trimethylsilyl.