Enantioselective Copper-Catalyzed Desymmetric Olefination via the Boron-Wittig Reaction

Boron-Wittig reactions represent one of the important
tools for
stereoselective synthesis of multisubstituted alkenes. However, using
this strategy to build chiral frameworks is an extreme challenge.
Here, we present an enantioselective boron-Wittig olefination of bis[(pinacol)boron]methane
with biaryl dialdehydes. This protocol was facilitated by a Cu/SOP
catalytic system and offered an efficient desymmetrization for the
synthesis of axially chiral aryl alkenes. The good reactivity, outstanding
selectivity (chem and enantio), broad substrate and functionality
tolerance, and diverse product transformations ensured the potential
broad applicability. The stereoselectivity of the reaction was intricately
linked to a halogen ion, and a reasonable catalytic cycle was proposed.