Synthesis of alpha-Borylmethyl-(E)-allylborons via Cu-Catalyzed Diboration of 1-Substituted Allenols and Their Application in Stereoselective Aldehyde Allylation

Abstract

1,2-Diborons with one boron atom each in the allyl and homoallyl positions are of great utility, especially as doubleallylation reagents. However, only a few synthetic methods have been reported to date and have a limited substrate scope. Herein, we developed the Cu-catalyzed regio- and stereoselective synthesis of alpha-borylmethyl-(E)-allylborons from easily accessible 1-substituted allenols and bis(pinacolato)diboron. Importantly, this method allowed the highly efficient and regioselective formation of doubleallylating diborons with diverse substituents, which would be otherwise cumbersome to synthesize, and could be successfully performed on a gram scale. The synthetic application of alpha-borylmethyl-(E)-allylborons was demonstrated by the enantio- and (Z)selective allylation of aldehydes via Brunsted acid catalysis. Furthermore, (E)-allyl and (E)-homoallyl diols with excellent diastereoselectivity were generated by the Lewis acid catalyzed diastereo- and (E)-selective allyl transfer of (E)-allyldiborons to aldehydes. Using this strategy, the key intermediate in the construction of the C7-C12 fragment of (-)-discodermolide was also synthesized.