Synlett 2007(4): 0538-0542  
DOI: 10.1055/s-2007-967960
LETTER
© Georg Thieme Verlag Stuttgart · New York

Enantioselective α-Oxytosylation of Ketones Catalysed by Iodoarenes

Robert D. Richardsona, T. Keri Pagea, Sabine Altermanna, Shauna M. Paradineb, Andrew N. Frenchb, Thomas Wirth*a
a Cardiff University, School of Chemistry, Park Place, Cardiff CF10 3AT, UK
Fax: +44(29)20876968; e-Mail: [email protected];
b Chemistry Department, Albion College, Albion, MI 49224, USA
Further Information

Publication History

Received 11 December 2006
Publication Date:
21 February 2007 (online)

Abstract

The α-oxytosylation of ketones catalysed by enantioenriched iodoarenes using mCPBA as stoichiometric oxidant is reported to give useful synthetic intermediates in good yield and modest enantioselectivity. We believe this to be the first report of an enantioselective catalytic reaction involving hypervalent iodine ­reagents which should open up a new field for enantioselective ­organocatalysis of oxidation reactions.

    References and Notes

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7

Commerical mCPBA obtained as a 70-77% mixture with H2O and mCBA is used in the reaction without any attempts at purification or drying. We find that this performs as well as mCPBA that has been dried before use, obviating the need for the dangerous drying process.

9

After seeing results of Y. Kita (Dohi, T.; Maruyama, A.; Minamitsuji, Y.; Takenaga, N.; Kita, Y. Chem. Commun. 2007, DOI: 10.1039/b616510a, in press) in which 2,2,2-trifluoroethanol can be used as solvent to increase the rate of oxidation of 4-iodotoluene by mCPBA, we applied to the iodobenzene-catalysed oxytosylation of propiophenone but this gave no increase in reaction rate.

12

Representative Experimental Procedure
A solution of propiophenone (1, 67 mg, 0.5 mmol) in MeCN (1 mL) was added to a solution of iodoarene 5 (15 mg, 0.05 mmol) TsOH·H2O (285 mg, 1.5 mmol) and mCPBA (366 mg, 77% wet with H2O, 1.5 mmol) in MeCN (2 mL) at r.t. The resulting solution was stirred at r.t. for 60 h then quenched by addition of sat. aq Na2S2O3 (5 mL) and sat. aq Na2CO3 (5 mL). The mixture was extracted with EtOAc (3 × 5 mL), the combined organic layers were washed with brine (10 mL), dried over Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by flash column chromatography (SiO2, 80:20 hexane-EtOAc) to yield tosylate 3 (119 mg, 0.39 mmol, 78%) as a white powder. The ee was determined by HPLC on the crude and purified products: Chiracel OB-H column, 40:60 hexane-2-PrOH, 0.5 mL·min-1, 40 °C, t R = 18.1 min (R), 21.6 min (S).