Scalable Ruthenium-Catalyzed Asymmetric Synthesis of a Key Intermediate for the β2-Adrenergic Receptor Agonist

An enantioselective and robust synthetic process to obtain a useful intermediate for the β2-adrenergic receptor agonist is described. Asymmetric transfer hydrogenation of ketone 1c by (S,S)-3b (Ms-DENEB) afforded chiral alcohol 2c in 71% isolated yield and 99% ee. The deprotection completed the synthesis of (R)-5 in 41% overall yield from 1b, which is readily commercially available.