Practical by Ligand Design: A New Class of Monodentate Phosphoramidite Ligands for Rhodium‐Catalyzed Enantioselective Hydrogenations

A new class of low‐cost and easy‐to‐prepare monodentate phosphoramidite ligands (CydamPhos) has been developed from readily accessible and cheap trans ‐1,2‐diaminocyclohexane as starting material through a three‐step transformation. This type of ligands exhibited excellent enantioseletivities and high activities in rhodium(I)‐catalyzed asymmetric hydrogenations of dehydro‐α‐amino acid methyl esters 9 ( ee : 96.2–99.8 %) and acetylenamides 11 (91.8–98.8 %). The remarkable substituent effects exhibited by the ligands on the enantioselective control of the catalysis are rationalized on the basis of molecular structure of the catalyst precursor.