The Chemistry of The Sharpless Asymmetric Epoxidation
- In 1980, K. B. Sharpless (then at the Massachusetts Institute of Technology,
presently at the University of California San Diego, Scripps research Institute;
co-winner of the Nobel Prize for Chemistry in 2001) and co-workers reported the
“Sharpless asymmetric epoxidation”.
- Sharpless epoxidation involves treating an allylic alcohol with titanium(IV)
tetraisopropoxide [Ti(O–iPr) 4 ], tert-butyl hydroperoxide [t-BuOOH], and a
specific enantiomer of a tartrate ester.
OH OH
O
tert-BuOOH, Ti(O−Pri) 4
CH 2 Cl 2 , − 20 oC
(+)-diethyl tartate
Geraniol
77% yield
95% enantiomeric excess
- The oxygen that is transferred to the allylic alcohol to form the epoxide is derived
from tert-butyl hydroperoxide.
- The enantioselectivity of the reaction results from a titanium complex among the
reagents that includes the enantiomerically pure tartrate ester as one of the ligands.
R^3 OH
R^2 R^1
":O:.. "
":O:.. "
D-(−)-diethyl tartrate (
OH, T
O
unnatural)
L-(+)-diethyl tartrate (natural)
t-BuO i(OPr-i) 4
CH 2 Cl 2 , − 20 oC OH
R^2 R^1
R^3
70-87% yields
> 90% e.e.
“The First Practical Methods for Asymmetric Epoxidation”
Katsuki, T.; Sharpless, K. B. J. Am. Chem. Soc. 1980 , 102 , 5974-5976.
