Asymmetric hydroesterification of styrene using catalysts with planar-chiral ferrocene oxazoline ligands

Chiral P,N-ferrocene ligands, 1-diphenylphosphino-1′-(S)-4-isopropyl-2.5-oxazolinyl]-2′-(S_p)-(trimethylsilyl)-ferrocene and its diastereomer, and 1-diphenylphosphino-1′-(S)-4-isopropyl-2.5-oxazolinyl]-2′(S_p)-(diphenylphosphino)-ferrocene and its diastereomer were used in the palladium-catalyzed asymmetric hydroesterification of styrene. The role of these ligands, which contain central, axial, and planar chirality, on the stereochemical outcome was investigated. A significant effect of using CuCl₂ as a co-catalyst on the reaction was observed. Excellent regioselectivity (b/n >99:1) with low ee (28%) was obtained in the presence of CuCl₂; moderate enantioselectivity (64% ee) but low regioselectivity (b/n, 40/60) was obtained in the absence of CuCl₂.