Selective Synthesis of Alkylboronates by Copper(I)-Catalyzed Borylation of Allyl or Vinyl Arenes

An efficient copper-catalyzed borylation reaction of allyl or vinyl arenes with bis(pinacolato)diboron has been developed, without using ligands. Markovnikov-selectivity is observed in the borylation of allyl arenes with bis(pinacolato)diboron, while the regioselectivity is completely opposite when styrene derivatives are used as substrates. A mechanism involving CuB species regioselectively adding olefin double bonds to form the alkylcopper or ?3-benzyl copper intermediate, which is followed by protonation to obtain products, is proposed