Synthesis of Quaternary Carbon Stereocenters by Copper-Catalyzed Asymmetric Allylic Substitution of Allyl Phosphates with Arylboronates

A copper-catalyzed
asymmetric allylic substitution of γ,γ-disubstituted
allyl phosphates with arylboronates has been developed for the construction
of quaternary stereocenters. High regio- and enantioselectivities
have been achieved by employing a hydroxy-bearing chiral N-heterocyclic carbene ligand, and both E and Z substrates provide the same enantiomer as the major product.
The mechanistic aspect of this catalysis has also been investigated
to find that a 1:1 copper/ligand complex is most likely responsible
for the present asymmetric catalysis, and the reaction proceeds with
almost perfect 1,3-anti stereochemistry with respect
to the allylic electrophile.