Enantiomeric Purity Of Alcohols Research Articles

Asymmetric Hydrosilylation of 1-Alkenes Catalyzed by Palladium–MOP

Abstract Asymmetric hydrosilylation of simple terminal alkenes (RCH=CH2) with trichlorosilane at 40 °C in the presence of 1 × 10−3 or 1 × 10−4 molar amounts of palladium catalyst prepared in situ from [PdCl(η3-C3H5)]2 and (S)-2-diphenylphosphino-2′-methoxy-1,1′-binaphthyl ((S)-MeO-MOP) proceeded with unusual regioselectivity and with high enantioselectivity to give high yields of 2-(trichlorosilyl)alkanes together with a minor amount of 1-(trichlorosilyl)alkanes. Optically active alcohols, RCH(OH)CH3, were obtained by oxidation of the carbon–silicon bond. Regioselectivities for forming 2-silylalkanes over 1-silylalkanes and enantiomeric purities of alcohols are as follows: R = n-C4H9: 89/11, 94% ee (R). R = n-C6H13: 93/7 95% ee (R). R = n-C10H21: 94/6, 95% ee (R). R = PhCH2CH2: 81/19, 97% ee (S). R = PhCH2CH2CH2: 80/20, 92% ee (R). R = cyclo-C6H11: 66/34, 96% ee (R). A similar hydrosilylation of 1-alkenes, 4-pentenyl benzoate and 1,5-heptadiene gave corresponding 2-alkanols of 90% ee and 87% ee, respectively, the ester carbonyl and the internal double bond remaining intact.

Determination of the absolute configuration and enantiomeric purity of alcohols from the 13C‐NMR spectra of the corresponding MTPA esters

AbstractFrom a study of the 13C‐shift values of the MTPA esters of 3‐substituted cyclohexanols of known absolute configuration an empirical rule has been developed to determine the absolute configuration of chiral cyclohexanols. The method is based on the Dale–Mosher model, which was originally developed for 1H‐NMR spectra. The scope and limitations of this method are discussed. The enantiomeric purity of the alcohols can be determined simultaneously by integration of the signals in well‐resolved diastereotopic carbon pairs.