title: Asymmetric conjugate 1,4-addition of arylboronic acids to alpha, beta-unsaturated esters catalyzed by Rhodium(I)/(S)-binap
abstract: Arylboronic acids underwent the conjugate 1,4-addition to alpha, beta-unsaturated esters to give beta-aryl esters in high yields in the presence of a rhodium(I) catalyst. The addition of arylboronic acids to isopropyl crotonate resulted in high yields and high enantioselectivity exceeding 90% ee in the presence of 3 mol % of Rh(acac)(C(2)H(4))(2) and (S)-binap at 100 degrees C. The rhodium/(S)-binap complex provided (R)-3-phenylbutanoate in the addition of phenylboronic acid to benzyl crotonate. The effects on the enantioselectivity of chiral phosphine ligands, rhodium precursors, and substituents on alpha,beta-unsaturated esters are discussed, as well as the mechanistic aspect of the catalytic cycle.
authors.affiliation: Division of Molecular Chemistry, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan.
authors.initials: S
authors.lastname: Sakuma
authors.initials: M
authors.lastname: Sakai
authors.initials: R
authors.lastname: Itooka
authors.initials: N
authors.lastname: Miyaura