Add time:09/04/2019         Source:sciencedirect.com

Fiftyeight prochiral ketones have been used inenantioselective hydrosilylation with diphenylsilane promoted by in-situ catalysts consisting of [Rh(cod)Cl]2 and the chiral ligands (4S-2-methyl-2-(2-pyridyl)-4-carbomethoxy-1,3-thiazolidine (A) and (4S)-2-(2-pyridyl)-4-carbethoxy-1,3-thiazolidine (B). Hydrolysis of the silyl ethers gave the corresponding secondary alcohols. Aryl methyl ketones were reduced with ee's better than 80% irrespective of whether the substituents Me, Cl, F, OMe were in o-, m-,. or p-position of the phenyl ring. The only exceptions were ketones containing the p-OMe substituent, for which a “p-methoxy effect” diminished the optical yields. Heterocyclic ketones were also hydrosilylated with high optical inductions, e.g. 2-acetylpyridine with 88.5% ee. Linear alkyl ketones with the CO group in the 2-position (methyl ketones) gave up to 50% ee R, in contrast to the corresponding ethyl ketones with the CO group in 3-position, which gave predominantely S-configurated products. In 35 cases the asymmetric inductions were higher with ligand B than with ligand A.

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