245503-15-5Relevant academic research and scientific papers
Catalytic enantioselective hydrosilylation of ketones with rhodium- phosphite complexes containing a TADDOLate and a dihydrooxazole unit
Heldmann, Dieter K.,Seebach, Dieter
, p. 1096 - 1110 (1999)
New types of chiral phosphorus/nitrogen ligands, capable of forming six- membered-ring metal chelates have been prepared from α,α,α',α'-tetraaryl- 1,2-dioxolane-4,5-dimethanols (TADDOLs), PCl3, and dihydrooxazole 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 ketones with Ph2SiH2/0.01 equiv. Rh1·7 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)-α,α- dimethyl-4-isopropyl-4,5-dihydrooxazole-2-methanol gives better results than the (R,R,S)-isomer (7d vs. 7c in Scheme 3), and an i-Pr group on the 4,5- dihydrooxazole 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 oxo groups (Scheme 4).
