Convenient General Asymmetric Synthesis of Roche Ester Derivatives through Catalytic Asymmetric Hydrogenation: Steric and Electronic Effects of Ligands

An efficient and concise asymmetric hydrogenation of acrylate esters promoted by the cationic ruthenium monohydride complex Ru(H)(η⁶‐cot)SYNPHOS]⁺BF₄^? is reported. A full investigation of the effects of catalyst precursors, solvents, temperature, hydrogen pressure, substrates as well as steric and electronic properties of ligands was carried out. The corresponding valuable Roche ester derivatives were obtained in good to excellent isolated yields and high enantioselectivities under mild conditions. The robustness and practicability of this highly enantioselective hydrogenation was demonstrated by the synthesis of the 3‐hydroxy‐2‐methylpropanoic acid tert‐butyl ester on a multigram scale, resulting in excellent yield and ee up to 94%.