Catalytic enantioselective hydrosilylation of ketones with rhodium-phosphite complexes containing a TADDOLate and a dihydrooxazole unit

New types of chiral phosphorus/nitrogen ligands, capable of forming six-mem bered-ring metal chelates have been prepared from alpha,alpha,alpha',alpha' -tetraaryl-1,2-dioxolane-4,5-dimethanols (TADDOLs), PCl3, and dihydrooxazol e alcohols (from amino acids) (7 in Scheme 1). The X-ray crystal structure of a Rh complex of one of these ligands, 8b, has been determined (Scheme 2 and Fig.). Enantioselective hydrosilylations of dialkyl and aryl alkyl keto nes with Ph2SiH2/0.01 equiv. Rh-1.7 have been studied and found to provide secondary alcohols in enantiomer ratios of up to 97: 3 (Scheme 3 and Table) . The ligand prepared from (R,R)-TADDOL and the (R)-valine-derived (R)-alph a,alpha-dimethyl-4-isopropyl-4,5-dihydro gives better results than the (R,R ,S)-isomer (7d vs. 7c in Scheme 3), and an i-Pr group on the 4,5-dihydrooxa zole ring gives rise to a slightly better selectivity than a Ph group. With the (R,R,R)-ligands the hydrogen transfer occurs from the Re face of the o xo groups (Sclleme 4).