A general synthesis of chiral 4,5-dihydro-3H-dinaphthophosphepines 1a–g is described. The resulting ligands represent a new class of monodentate chiral phosphines. First applications of 1a–g in the rhodium-catalyzedasymmetrichydrogenation of unsaturated carboxylic acid derivatives demonstrate the usefulness of our ligands. Enantioselectivities up to 95% ee for the hydrogenation of methyl α-acetamidocinnamate
The rhodium-catalyzed asymmetric hydrogenation of different acyclic and cyclic enol carbarnates to give optically active carbarnates has been examined in the presence of chiral monodentate ligands based on a 4,5-dihydro-3H-dinaphthophosphepine motif 4. The enantioselectivity is largely dependent upon the reaction conditions, the nature of substituents on the phosphorus ligand and structure of the enol carbamate. By applying the optimized reaction conditions, enantioselectivities of up to 96% ee have been achieved. (c) 2007 Elsevier Ltd. All rights reserved.
Enantioselective Hydrogenation ofβ-Ketoesters with Monodentate Ligands