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R. D. Richardson et al.
LETTER
(2) Kita, Y. In Topics in Current Chemistry, Vol. 224; Wirth, T.,
Ed.; Springer: Berlin/Heidelberg, 2002, 209.
(3) (a) Stang, P. J.; Zhdankin, V. V. Chem. Rev. 1996, 96, 1123.
(b) Varvoglis, A. Tetrahedron 1997, 53, 1179.
(4) Hirt, U. H.; Schuster, M. F. H.; French, A. N.; Wiest, O. G.;
Wirth, T. Eur. J. Org. Chem. 2001, 1569.
(5) For a review, see: Richardson, R. D.; Wirth, T. Angew.
Chem. Int. Ed. 2006, 45, 4402.
is needed in the iodoarene in order to obtain high enan-
tioselectivities. This is consistent with our earlier studies
that suggest a pseudocyclic intermediate is formed in such
iodanes.1f,4
In conclusion, we have developed the first enantioselec-
tive oxidiation catalysed by substoichiometric quantities
of iodoarenes. Synthetically useful a-tosyloxyketones3
can be obtained in good yield and modest enantiomeric
excess. In addition to this, many iodoarenes can be tested
for enantio-induction that could not be investigated before
and this will surely enhance understanding of the enan-
tioselectivity observed in chiral hypervalent iodine chem-
istry as well as increase the range of chiral iodoarenes that
can be evaluated. Studies into further enantioselective
catalytic reactions, understanding the origin of selectivity
and improved iodoarene catalysts are currently underway.
(6) Yamamoto, Y.; Togo, H. Synlett 2006, 798.
(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.
(8) Brown, K. J.; Berry, M. S.; Waterman, K. C.; Lingenfelter,
D.; Murdoch, J. J. Am. Chem. Soc. 1984, 106, 4717.
(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.
Acknowledgment
We thank Prof. Bernhard Witulski (University of Mainz, Germany)
for valuable discussions, Ms. Christine Richter (University of
Kaiserslautern, Germany) and Mr. A. Masih Bahar (University of
Münster, Germany) for the synthesis of 18 and Cardiff University
for support. We also thank the EPSRC National Mass Spectrometry
Service Centre, Swansea, for mass spectrometric data and EPSRC
for funding this project. We thank The National Science Foundation
(INT-0209956) and Albion College (FDC and FURSCA) for fun-
ding (A.N.F. and S.M.P.).
(10) Page, T. K.; Wirth, T. Synthesis 2006, 3153.
(11) For examples, see: Hamamoto, H.; Anilkumar, G.; Tohma,
H.; Kita, Y. Chem. Eur. J. 2002, 8, 5377; and references
cited therein.
(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, tR = 18.1 min (R), 21.6 min (S).
(13) Ochiai, M. In Chemistry of Hypervalent Compounds; Akiba,
K., Ed.; Wiley-VCH: New York, 1999, 359.
References and Notes
(1) (a) Hatzigrigoriou, E.; Varvoglis, A.; Bakola-
Christianopoulou, M. J. Org. Chem. 1990, 55, 315. (b)Ray,
D. G.; Koser, G. F. J. Am. Chem. Soc. 1990, 112, 5672.
(c) Kitamura, T.; Lee, C. H.; Taniguchi, Y.; Fujiwara, Y.;
Matsumoto, M.; Sano, Y. J. Am. Chem. Soc. 1997, 119, 619.
(d) Ochiai, M.; Kitagawa, Y.; Takayama, N.; Takaoka, Y.;
Shiro, M. J. J. Am. Chem. Soc. 1999, 121, 9233. (e) Wirth,
T.; Hirt, U. H. Tetrahedron: Asymmetry 1997, 8, 23.
(f) Hirt, U. H.; Spingler, B.; Wirth, T. J. Org. Chem. 1998,
63, 7674. (g) Tohma, H.; Takizawa, S.; Watanabe, H.;
Fukuoka, Y.; Maegawa, T.; Kita, Y. J. Org. Chem. 1999, 64,
3519. (h) Ladziata, U.; Carlson, J.; Zhdankin, V. V.
Tetrahedron Lett. 2006, 47, 6301.
(14) Moriarty, R.; Prakash, O.; Duncan, M. P. J. Chem. Soc.,
Perkin Trans. 1 1987, 559.
Synlett 2007, No. 4, 538–542 © Thieme Stuttgart · New York