A Versatile Bis-Allylboron Reagent for the Stereoselective Synthesis of Chiral Diols

Abstract

Allylboron reagents are popular in synthesis owing to their versatility and the predictable stereochemical outcomes of their reactions with carbonyl compounds. Herein, we describe the synthesis of (Z,Z)-hexadienyl bis-boronate 1, a configurationally stable, crystalline, and easy to handle compound, which represents a class of bis-allylic boron reagents with heretofore untapped synthetic potential. In combination with a chiral phosphoric acid catalyst, the reagent can be employed for the enantioselective allyl transfer reaction to a variety of one-pot transformations, enabling swift access to functionalized 1,n-diols. The in situ conversion of the reagent into the corresponding bis-borinic ester allows for the direct and diastereoselective two-fold allyl transfer to aldehydes. This affords C₂ - or C_i -symmetric stereotetrads containing a 1,4-diol moiety for natural product synthesis. The usefulness of our method was demonstrated with a short synthesis of the lignan (±)-neo-olivil.

Keywords: allyboron; chiral phosphoric acid; natural products; stereospecific reactions; synthetic methods.