Enantioselective Syntheses of (<i>Z</i>)-6′-Boryl-<i>anti</i>-1,2-oxaborinan-3-enes via a Dienylboronate Protoboration and Asymmetric Allylation Reaction Sequence

Abstract

The enantioselective synthesis of 6′-boryl-anti-1,2-oxaborinan-3-enes is reported. A Cu-catalyzed highly stereoselective 1,4-protoboration of 1,1-bisboryl-1,3-butadiene is developed to generate (E)-α,δ-bisboryl-crotylboronate. The chiral phosphoric-acid-catalyzed asymmetric allylboration of aldehydes with the boron reagent produces 6′-boryl-anti-1,2-oxaborinan-3-enes with excellent Z-selectivities and enantioselectivities. The product contains a vinyl and alkyl boronate unit that can directly participate in a variety of subsequent transformations.

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