By: William Sommer and Daniel Weibel, ChemFiles 2008, 8.2, 81.

Rewarded by a Nobel Prize in 2001 for his pioneering work in asymmetric synthesis, Knowles was the first to develop a transition-metal chiral catalyst based on a chiral diphosphine ligand, DIPAMP, that could transfer chirality to a prochiral substrate with high enantiomeric excesses. He demonstrated that a chiral diphosphine chelated to rhodium could give access to catalysis mimicking enzyme selectivity. To demonstrate the activity and selectivity of this new ligand, Knowles synthesized L-DOPA, a treatment for Parkinson's disease, requiring the selective hydrogenation of an alkene. The synthesis of L-DOPA starts with the asymmetric hydrogenation of (Z)-2‑acetamido-3-(3,4‑dihydroxyphenyl)acrylic acid using the Rh-DIPAMP complex followed by deprotection of the amine. This process has been scaled up at Monsanto (Scheme 1). 1

Scheme 1

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  1. Knowles, W. S. Acc. Chem. Res. 1983, 16, 106.

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