Monodentate phosphites with carbohydrate substituents and their application in rhodinm catalysed asymmetric hydrosilylation reactions

Several monodentate phosphites derived from D-glucofuranose were prepared a nd examined as ligands in the rhodium catalysed enantioselective hydrosilyl ation of acetophenone. A substantial Variation in the e.e. values, from rac emic to 58% e.e., was seen depending on the nature of the phosphite ligand used and the ligand to metal ratio. The reactivity of the selected phosphit e P(DAG)(3) towards [Rh(mu -Cl)(COD)](2) and [Rh(mu -Cl)(C2H4)(2)](2) (DAG= (1:2;5:6)-di(O-isopropylidene)-D-glucofuranosyl) allowed the synthesis of m onosubstitued Rh(Cl)(COD)P(dag), and [Rh(mu -Cl)(C2H4)P(dag)(3)](2) complex es, and the disubstituted Rh(Cl)(P(dag)(3))(2) and Rh(Cl)(C2H4)(P(dag)(3))( 2) complexes. This study indicated that the disubstituted compounds offer b etter enantioselectivities than the monosubstituted ones. (C) 2001 Elsevier Science Ltd. All rights reserved.