Versatile Homoallylic Boronates by Chemo- SN2’- Diastereo- and Enantioselective Catalytic Sequence of Cu–H Addition to Vinyl–B(pin)/Allylic Substitution

摘要

A highly chemo-, diastereo- and enantioselective catalytic method that efficiently combines a silyl hydride, vinyl–B(pin) (pin = pinacolato) and (E)-1,2-disubstituted allylic phosphates is introduced. Reactions, best promoted by a Cu-based complex with a chiral sulfonate-containing N-heterocyclic carbene, are broadly applicable. Aryl-, heteroaryl-, alkenyl, alkynyl and alkyl-substituted allylic phosphates may thus be converted to the corresponding homoallylic boronates and then alcohols (after C–B bond oxidation) in 46–91% yield and in up to >98% SN2’:SN2 ratio, 96:4 diastereomeric ratio and 98:2 enantiomeric ratio. The reasons why an NHC–Cu catalyst is uniquely effective (vs. the corresponding phosphine systems) and the basis for different trends in stereoselectivity are provided with the aid of DFT calculations.