Catalytic Enantioselective Hydrosilylation of Aromatic Ketones Using Rhodium Complexes of TADDOL‐Derived Cyclic Phosphonites and Phosphites

Cyclic phosphonites and phosphites 2–4 are readily available from Cl 2 PR and ( R,R )‐ or ( S,S )‐α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols (= TADDOLs 1 , which, in turn, are only two steps away from tartrate); the X‐ray crystal structure of one representative, the phenyl phosphonite 2b , was determined. Five previously described and six new ones of the chiral P derivatives were tested as ligands for Rh I ‐ and Pd O ‐catalyzed reactions such as hydrocarbonylations, hydroborations, and hydrosilylations of CC bonds; while the resulting catalysts were highly active and regioselective, they did not lead to useful enantiomer enrichment in the products ( Scheme 1 ). In contrast, hydrosilylation of phenyl and 2‐naphthyl methyl or ethyl ketone by Ph 2 SiH 2 (1.2 equiv.) gave, after desilylation, the corresponding secondary alcohols of ( R )‐configuration with up to 87% ee in the presence of 0.1 equiv. of the penta(2‐naphthyl)‐substituted phosphonite 3d and 0.02 mol‐equiv. of Rh ( Table 1 ).