C O M M U N I C A T I O N S
Table 2. Catalytic R-Acetoxylation of Ketones with m-CPBAa
Scheme 2
(OAc)OCOAr (Ar ) m-ClC6H4).11 Ligand exchange of a (diacyl-
oxyiodo)benzene with an enol derived from a ketone through the
formation of tetracoordinated iodate1c produces an R-λ3-iodanyl
ketone, which on SN2 displacement by acetic acid affords an
R-acetoxy ketone with liberation of PhI.12 The effect of added water
in this catalytic oxidation is interesting; however, we found that
the presence of water slows down the rate of enolization of
acetophenone (Figure S2) as well as slightly decreases the rate of
oxidation of iodobenzene by m-CPBA to λ3-iodanes (Figure S3).
In summary, we have developed an efficient method for catalytic
R-oxidation of ketones. The method involves in situ generation of
hypervalent phenyl-λ3-iodanes by the oxidation of a catalytic amount
of iodobenzene with m-CPBA.
Supporting Information Available: Text giving experimental
details, Scheme S1, Figures S1-S4, and Tables S1 and S2. This material
References
(1) (a) Varvoglis, A. The Organic Chemistry of Polycoordinated Iodine;
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Curr. Chem. 224; Springer: Berlin, 2003.
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273. (b) Moriarty, R. M.; Vaid, R. K.; Koser, G. F. Synlett 1990, 365.
(4) (a) Fuchigami, T.; Fujita, T. J. Org. Chem. 1994, 59, 7190. (b) Fujita, T.;
Fuchigami, T. Tetrahedron Lett. 1996, 37, 4725.
(5) (a) Reich, H. J.; Peake, S. L. J. Am. Chem. Soc. 1978, 100, 4888. (b)
Cambie, R. C.; Lindsay, B. G.; Rutledge, P. S.; Woodgate, P. D. J. Chem.
Soc., Chem. Commun. 1978, 919. (c) Morris, D. G.; Shepherd, A. G. J.
Chem. Soc., Chem. Commun. 1981, 1250. (d) Davidson, R. I.; Kropp, P.
J. J. Org. Chem. 1982, 47, 1904. (e) Yamamoto, S.; Itani, H.; Tsuji, T.;
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Shepherd, A. G. J. Chem. Soc., Chem. Commun. 1981, 1250. (g) Tohma,
H.; Maruyama, A.; Maeda, A.; Maegawa, T.; Dohi, T.; Shiro, M.; Morita,
T.; Kita, Y. Angew. Chem., Int. Ed. 2004, 43, 3595.
a Reaction conditions: ketone (0.25 M) in acetic acid, m-CPBA (2 equiv),
PhI (0.1 equiv), H2O (5 equiv), and BF3‚Et2O (3 equiv) at 25-30 °C for
20-48 h under argon. b Isolated yields. Parentheses are GC yields. c H2O
(3 equiv). d PhI (0.3 equiv). e m-CPBA (1.4 equiv) and PhI (0.3 equiv).
R-methylene groups toward acetoxylation decreases in the order
ethyl > pentyl > nonyl. This tendency is in good agreement with
the preferred direction for the reported acid-catalyzed enolization
of unsymmetrical ketones.9 Steric effects appear to be significant
in the oxidation of 4,4-dimethyl-2-pentanone, in which the meth-
ylene group that is flanked by a tert-butyl group is less reactive
than the methyl group (entry 15).10
A catalytic cycle for this oxidation is shown in Scheme 2. BF3‚
Et2O accelerates oxidation of iodobenzene to (diacyloxyiodo)-
benzenes by m-CPBA, being completed within 10 min under our
conditions. Because of the facile ligand exchange on iodine(III),1c
PhI(OAc)2 is produced as a major λ3-iodane in the reaction, along
with the formation of small amounts of PhI(OCOAr)2 and PhI-
(6) 1H NMR analyses showed that commercially available m-CPBA is
contaminated with a various degree (17-33%) of water and with 10-
15% of m-chlorobenzoic acid, depending on the commercial source, and
therefore it was dried under vacuum for 1 h at room temperature prior to
use, which leads to reproducible results.
(7) Renz, M.; Meunier, B. Eur. J. Org. Chem. 1999, 737.
(8) Dohi, T.; Maruyama, A.; Yoshimura, M.; Morimoto, K.; Tohma, H.; Shiro,
M.; Kita, Y. Chem. Commun. 2005, 2205.
(9) Rappe, C.; Sachs, W. H. J. Org. Chem. 1967, 32, 3700.
(10) Hatzigrigoriou, E.; Varvoglis, A.; Bakola-Christianopoulou, M. J. Org.
Chem. 1990, 55, 315.
(11) A mixture of equal amounts of PhI(OAc)2 and PhI(OCOAr)2 (Ar )
m-ClC6H4) in CDCl3 at 22 °C reaches equilibrium within 1 h via ligand
exchange, yielding a statistical 1:2:1 mixture of PhI(OAc)2, PhI(OAc)-
OCOAr, and PhI(OCOAr)2 (Figure S4).
(12) Ochiai, M.; Nishitani, J.; Nishi, Y. J. Org. Chem. 2002, 67, 4407.
JA0542800
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