Nonracemic Allylic Boronates through Enantiotopic-Group-Selective Cross-Coupling of Geminal Bis(boronates) and Vinyl Halides

Under the influence
of a chiral palladium catalyst, 1,1-bis­(pinacolboronate)
esters undergo asymmetric cross-coupling with bromoalkenes to generate
nonracemic allyl boronates with high levels of enantioselectivity.
The so-formed allyl boronates may be oxidized with hydrogen peroxide
to provide secondary allylic alcohols or with nitrosobenzene to furnish
nonracemic tertiary allylic alcohols. Mechanistic experiments suggest
the operation of a pathway involving outer-sphere stereoinvertive
transmetalation.