Axel Monsees

Synthesis of new chiral monodentate phosphines and their use in asymmetric hydrogenation

Abstract A general synthesis of chiral 4,5-dihydro-3 H -dinaphthophosphepines 1a – g is described. The resulting ligands represent a new class of monodentate chiral phosphines. First applications of 1a – g in the rhodium-catalyzed asymmetric hydrogenation of unsaturated carboxylic acid derivatives demonstrate the usefulness of our ligands. Enantioselectivities up to 95% ee for the hydrogenation of methyl α-acetamidocinnamate were obtained in the presence of 1d . This result represent the highest enantioselectivity reported for asymmetric hydrogenation in the presence of monodentate phosphines.

Synthesis of new chiral monodentate aminophosphinites and their use in catalytic asymmetric hydrogenations

Abstract A general synthesis of chiral 4-amino-4,5-dihydro-3H-dinaphthophosphepines 5a–f is described. The resulting monodentate chiral aminophosphinites have been tested in the rhodium-catalyzed asymmetric hydrogenation of methyl α-acetamidocinnamate and methyl α-acetamidoacrylate. Enantioselectivities up to 96% ee were obtained in the presence of 5a and sodium dodecylsulfonate in toluene.

Chiral pyrophosphites—synthesis and application as ligands in Rh(I)-catalyzed asymmetric hydrogenation

Abstract Enantiopure pyrophosphites have been prepared for the first time based upon two independent synthetic pathways. The new ligands based on binaphthols, which are remarkably stable towards oxidation, were tested in the Rh(I)-catalyzed asymmetric hydrogenation of functionalized olefins, where up to 70% ee could be achieved.

Chiral Oxo- and Oxy-Functionalized Diphosphane Ligands Derived from Camphor for Rhodium(I)-Catalyzed Enantioselective Hydrogenation

The synthesis of two series of diastereomeric oxo- and oxy-substituted diphosphanes 7a−9a and 7b−9b, as well as an analogous nonfunctionalized diphosphane 17, was performed starting from (R)-camphor. The new diphosphanes were used as ligands in the enantioselective rhodium(I)-catalyzed hydrogenation of functionalized olefins − α- and β-dehydroamino acids and their esters − in order to elucidate the effect of the oxo- and oxy-functional groups. The enantioselectivities, ranging from 2−90% ee, and the rates were strongly dependent on the type and relative position of the oxo or oxy substituent in the catalyst. Possible explanations for the effects are given. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

A new hydroxydiphosphine as a ligand for Rh(I)-catalyzed enantioselective hydrogenation

Abstract A new diphosphine ligand bearing a hydroxy group in the backbone was synthesized starting from 9-bromocamphor. The rhodium(I) complex based on this ligand was tested in the hydrogenation of α- and β-amino acid precursors. The activity and selectivity of the catalyst were found to be strongly dependent upon the nature of the substrate. Thus, β-acetylamino carboxylates were obtained with up to 97% ee.