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

Cyclic phosphonites and phosphites2–4are readily available from Cl2PR and (R,R)‐ or (S,S)‐α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols (= TADDOLs1, which, in turn, are only two steps away from tartrate); the X‐ray crystal structure of one representative, the phenyl phosphonite2b, was determined. Five previously described and six new ones of the chiral P derivatives were tested as ligands for RhI‐ and PdO‐catalyzed reactions such as hydrocarbonylations, hydroborations, and hydrosilylations of CC 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 Ph2SiH2(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 phosphonite3dand 0.02 mol‐equiv. of Rh (Table 1).