Mechanism and conditions for highly enantioselective epoxidation of α,β-enones using charge-accelerated catalysis by a rigid quaternary ammonium salt

Organic Letters

Volumn 1, Issue 8, 1999, Pages 1287-1290

  Corey, E J ^a   Zhang, Fu Yao ^a  

^a HARVARD UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EPOXIDE; INORGANIC SALT; KETONE; QUATERNARY AMMONIUM DERIVATIVE;

ARTICLE; CATALYSIS; CHEMISTRY; STEREOISOMERISM; SYNTHESIS;

CATALYSIS; EPOXY COMPOUNDS; KETONES; QUATERNARY AMMONIUM COMPOUNDS; SALTS; STEREOISOMERISM;

EID: 0033592480     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol990964z     Document Type: Article

References (30)

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22. Potassium hypochlorite solution (8.0 M) was prepared by treatment of 50% aqueous potassium hydroxide with chlorine and filtration of the precipitate of KCl. The resulting cold light straw-colored solution must be used promptly or stored at -20°C since it is unstable above 0°C. Potassium hypochlorite is superior to sodium hypochlorite because it leads to more rapid and more enantioselective epoxidation under phase transfer conditions with 2.
23. The epoxidation of a variety of α,α-enones with alkyl or other non-phenyl groups attached to carbonyl under the standard conditions defined herein leads to only modest enantioselection.
24. The beneficial effect of the 4-fluoro substituent in the examples of Table 1 relative to hydrogen (X = F or H) may be due to a stronger edge interaction of 4-fluorophenyl as compared with phenyl with the contacting quinoline ring, as shown in Figure 1.
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26. 4 (73%).
27. R = 59.9 min (minor).
28. R = 15.1 min (major).
29. R = 15.0 min (major).
30. Determination of Enantioselectivities for the Epoxidations Summarized in Table 1. HPLC analysis of the epoxy ketones listed in Table 1 were carried out using commercially available chiral columns with isopropyl alcohol-hexanes as eluent at 23°C and detection at 254 nm. For each product of Table 1, the corresponding enantiomers of a racemic reference sample of epoxy ketone were cleanly separated under the conditions used for analysis. The following chiral columns were used for the products in Table 1: for entries 1, 6, 7, and 13. Whelk 01 column (Regis Co.); for entries 2, 3, 11, and 14, OB-H column (Chiral Technologies Inc.); for entries 4, 9, 10, 12, and 15, OD column (Chiral Technologies Inc.); for entries 5 and 8, OJ column (Chiral Technologies Inc.).