Highly Diastereo- and Enantioselective Synthesis of 3,6′-Bisboryl-anti-1,2-oxaborinan-3-enes: An Entry to Enantioenriched Homoallylic Alcohols with A Stereodefined Trisubstituted Alkene

A Cu-catalyzed regio-, diastereo-, and enantioselective carboboration of 1,1-bisboryl-1,3-butadiene is developed to generate enantioenriched 3,6 '-bisboryl-anti-1,2-oxaborinan-3-enes. DFT calculations indicate that the initial diene 1,2-borocupration forms a (3)eta-allylic copper as the most stable intermediate. Subsequent aldehyde addition, however, operates under Curtin-Hammett control via a more reactive alpha,alpha-bisboryl tertiary allylcopper species to furnish products with high enantioselectivities. The three boryl groups in the products are properly differentiated and can undergo a variety of chemoselective transformations to produce enantioenriched homoallylic alcohols with a stereodefined trisubstituted alkene.