Highly Diastereo‐ and Enantioselective Syntheses of 3,6’‐Bisboryl‐anti‐1,2‐oxaborinan‐3‐enes: An Entry to Chiral 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 reveal that the initial diene 1,2-borocupration forms a  3 η- allylic copper as the most stable intermediate. However, subsequent aldehyde addition operates under the Curtin-Hammett principle via a less stable but more reactive α,α-bisboryl tertiary allylcopper species to furnish products with high enantioselectivities. Such reactivity via a tertiary allylic copper has no precedent in the literature. 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.