New Diphosphite Ligands for Catalytic Asymmetric Hydrogenation: The Crucial Role of Conformationally Enantiomeric Diols

Abstract

Efficient catalysis of asymmetric hydrogenations is possible with complexes of the type 1 which contain chiral diphosphites as ligands. Thus the Rh‐catalyzed hydrogenation of dimethyl itaconate with a catalyst containing 1,4:3,6‐dianhydro‐D‐mannite and conformationally enantiomeric diols is highly enantioselective.

One-pot multi-substrate enantioselective conjugate addition of diethylzinc to nitroalkenes

“…14,15 Phosphoramidite F, which contains the atropisomeric bisphenol moiety, 29 reported by Alexakis, 30 gives even higher enantioselectivities for almost all products, leading to 77% for 4c. For 4b 71% ee is obtained, whereas only moderate ees have been reported until now for this substrate.…”

Phosphonites Based on the Paracyclophane Backbone: New Ligands for Highly Selective Rhodium-Catalyzed Asymmetric Hydrogenation

“…See ref for bidentate phosphites having a chiral backbone and their use in rhodium-catalyzed hydrogenation of dimethyl itaconate. The stereochemistry of the product is determined by the stereochemistry of the P/O unit.…”

“…In conclusion, the synthesis of the common reactive intermediate pseudo-ortho-bis(dichlorophosphino)paracy- clophane (4) and the ready availability of the bisaryloxy building blocks has allowed the generation of a new class of phosphonites based on the paracyclophane backbone. Two ligands bearing the biphenoxy unit and the chiral binaphthoxy unit were identified as useful ligands for asymmetric hydrogenation.…”

“…Rhodium and ruthenium catalysts bearing chiral chelating diphosphine ligands have proved, over the past 30 years, to be the most effective catalysts for asymmetric hydrogenation. However, it has recently been shown that some of the results obtained with chelating phosphines can be matched by the use of bidentate phosphinites, phosphonites, phosphites, or phosphoroamidites . In addition, chiral monodentate phosphonites, phosphites, and phosphoroamidites 5 have in some cases proved to be as effective as the analogous bidentate ligands.…”

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“…10 Reetz has recently reported that asymmetric alkene hydrogenation with biphenyl-based bisphosphite ligands displays an analogous difference between ligand diastereomers. 11 Our results obtained using diastereomeric structures of 2 indicate that achiral transformations mediated by bisphosphites are likewise effected by ligand structure.…”