N-Phenylcampholylhydroxamic Acid

[62668-00-2]  · C16H23NO2  · N-Phenylcampholylhydroxamic Acid  · (MW 261.40)

(chiral ligand in asymmetric epoxidation of allylic alcohols1)

Solubility: sol toluene, acetonitrile.

Preparative Method: phenylhydroxylamine (2 equiv) is added to a solution of campholyl chloride (1 equiv) in acetonitrile.1

Asymmetric Epoxidation.

N-Phenylcampholylhydroxamic acid has been used as a chiral ligand in the transition metal-catalyzed asymmetric epoxidation of allylic alcohols.1 Three allylic alcohols [geraniol (1), (E)-a-phenylcinnamyl alcohol (2), and 1-hydroxymethyl-2-methylcyclohexene (3)] have been oxidized to the corresponding epoxides in the presence of the chiral hydroxamate complex of vanadium. The best asymmetric induction (50% ee) is observed for alcohol (2) at -78 °C. Generally, low temperature reactions give higher asymmetric inductions but lower yields. The optimum inductions are attained when a 5:1 ratio of hydroxamic acid and Vanadyl Bis(acetylacetonate) is used. t-Butyl Hydroperoxide gives substantially better inductions than Cumyl Hydroperoxide. The asymmetric oxidation is proposed to go through the intermediate (4),1,2 in which the alcohol is coordinated to the metal during the oxygen atom transfer step.

1. Michaelson, R. C.; Palermo, R. E.; Sharpless, K. B. JACS 1977, 99, 1990.
2. Chong, A. O.; Sharpless, K. B. JOC 1977, 42, 1587.

Sangho Koo

Myong Ji University, Seoul, Korea

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