Chiral Ketone Catalysts Derived from d-Fructose

Biographical Sketches

H.-Q. Ge was born in Hubei (China) in 1977. He achieved his ­Bachelor degree from the School of Chemistry and Material ­Science, Hubei University, China. He is currently in the second year of his Master-PhD through-train studies, working on the asym­metric epoxidation of olefins on organic-inorganic hybrid catalysts, under the supervision of Professors Q.-H. Xia and C.-P. Ye.

Introduction

In 1996, a new chiral ketone 1 (1,2;4,5-di-isopropylidene-d-erythro-2,3-hexodiuro-2,6-pyranose), derived from inexpensive d-fructose, was reported by Shi and co-workers as a highly active asymmetric epoxidation catalyst. [1] This rapidly developed into a new class of highly efficient catalysts for the asymmetric epoxidation of a wide range of olefins. [2]

Preparation

Ketones 1, 2 and 3 were prepared from d-fructose in excellent yields. [3a] [4] [5] Ketone 4 was prepared from d-glucose. [3c] [6]

Abstract

(A) Ketone 1 is an efficient epoxidation catalyst for trans-disubstituted and trisubstituted olefins with potassium peroxomonosulfate (Oxone) as the oxidant. [1] [3a] [7] Cheap dilute 30% H2O2, a green oxidant, shows an enantioselectivity comparable to that of Oxone. [8] [9]
(B) Hydroxyalkenes can be asymmetrically epoxidized by chiral ketone 1 with Oxone or H2O2. As shown, asymmetric epoxidation of trans-b-hydroxylmethylstyrene can be achieved in 98% ee and 85% yield. [10]
(C) A highly effective and mild asymmetric monoepoxidation of conjugated dienes with chiral ketone 1 and Oxone presents an ­efficient approach to prepare enantiomerically enriched vinyl ­epoxides. The enantiomeric excess for the major monoepoxides ranges from 89% to 97%. [11]
(D) For the asymmetric epoxidation of conjugated enynes using chiral ketone 1 as the catalyst and Oxone or H2O2 as the oxidant, a high ee up to 95% is obtained. [12] Double bonds in conjugated enynes can also be selectively epoxidized by ketone 2 and Oxone. [4]
(E) Chiral oxy-substituted epoxides or hydroxy ketones can be synthesized through the enantioselective epoxidation of chiral silyl enol ethers or enol esters catalyzed by ketone 1 and Oxone. [13]
(F) Through the asymmetric epoxidation of 2,2-disubstituted ­vinylsilanes, chiral 2,2-disubstituted a,b-epoxysilanes can be ­synthesized. [14] Upon desilylation, the corresponding 1,1-disub­stituted terminal epoxides are obtained without any loss in enantio­selectivity.
(G) The kinetic resolution of racemic 1,3- and 1,6-disubstituted ­cyclohexene via chiral ketone 1 has been demonstrated. [15]
(H) Asymmetric epoxidation of several trans-disubstituted and trisubstituted a,b-unsaturated esters was achieved with high yields and ee values, using a system consisting of ketone 2 and oxone. [4]
(I) For the asymmetric epoxidation of terminal olefins, ketone 1 shows a similar reactivity to ketone 4, but a much lower enantio­selectivity. [16]
(J) Ketone 1 shows both a lower reactivity and a lower enantio­selectivity than ketone 4 for the asymmetric epoxidation of cis-di­substituted olefins. [3]
(K) The enantioselectivity obtained with ketone 3 is very similar to that of ketone 1 in the asymmetric epoxidation of trans-disub­stituted and trisubstituted olefins, hydroxyalkenes and chiral enol esters. However, the catalyst consumption is greatly decreased from 20-30 mol% for ketone 1 to 1-5 mol% for ketone 3. [5]

References

• 1 Tu Y. Wang Z.-X. Shi Y. J. Am. Chem. Soc.  1996,  118:  9806 
• For leading references on asymmetric epoxidation catalyzed by chiral ketones see:
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• 2d Armstrong A. Hayter BR. Chem. Commun.  1998,  621 
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• 2f Frohn M. Shi Y. Synthesis  2000,  1979 
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• 9 Y_oxone or Y_H2O2 stands for the yield when Oxone or H₂O₂ is used as the oxidant; while Y₁,Y₃ or Y₄ stands for the yield when ketone 1, 3 or 4 is used as the catalyst
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