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DOI: 10.1055/sos-SD-021-00911

Whitehead, A.; Sieck, S. R.; Mukherjee, S.; Hanson, P. R.Science of Synthesis, (200521923.

Cationic rhodium catalysts have been used for the asymmetric hydrogenation of enamido[‌52‌] and enol esters.[‌53‌] These catalysts, in conjunction with C2-symmetric diphosphine ligands (DuPHOS and BPE, see Scheme 19), can also asymmetrically hydrogenate acylphosphonate enolates in good ee and yield of the resulting α-hydroxy phosphonates.[‌54‌] O-Alkylation of acylphosphonates, formed from acid chlorides 60 and trimethyl phosphite, with benzoic anhydride and 1,8-diazabicyclo[5.4.0]undec-7-ene affords a number of benzoyl enol ethers 61 exclusively as the E-isomer in 4386% yield (Scheme 19). Treatment of a benzoyl enol ether 61 with a rhodium catalyst under hydrogen pressure (4 atm) gives the desired product 62. Enantiomeric excess ranges from 6096% and either enantiomer can be obtained depending on the configuration of the chiral rhodium ligand.

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