A library of 20 monodentate phosphoramidite ligands has been prepared and applied in rhodium-catalyzed asymmetric hydrogenation. This resulted in the identification of two ligands, PipPhos and MorfPhos, that afford excellent and in several cases unprecedented enantioselectivities in the hydrogenation of N-acyldehydroamino acid esters, dimethyl itaconate, acyclic N-acylenamides, and cyclic N-acylenamides. In addition, a method for the parallel enantioselectivity determination of eight acylated amines is presented.

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In 2000, three research groups demonstrated that the widely held view that chiral bidentate ligands are necessary to achieve high enantioselectivity in rhodium-catalyzed hydrogenations needs revision. Monodentate phosphonites, [1a] phosphites [1b] and phosphoramidites [1c] proved to be highly versatile ligands for this important transformation and afforded excellent enantioselectivities for a broad range of substrates.

[reaction: see text] The synthesis and application of a new class of catechol-based phosphoramidites is described. Ees up to 99% were obtained in the rhodium-catalyzed asymmetric hydrogenation of dehydroamino acids and enamides.