ORGANIC
LETTERS
2002
Vol. 4, No. 16
2727-2730
Diverse Pathways for the
Palladium(II)-Mediated Oxidation of
Olefins by tert-Butylhydroperoxide
Jin-Quan Yu and E. J. Corey*
Department of Chemistry and Chemical Biology, HarVard UniVersity,
12 Oxford Street, Cambridge, Massachusetts 02138
Received May 23, 2002
ABSTRACT
New procedures are described for the palladium-catalyzed oxidation of olefins by tert-butylhydroperoxide under slightly basic conditions in
CH Cl2 solution at 0−25 °C.
2
The selective oxidative functionalization of organic com-
pounds under the catalytic influence of transition metal
complexes continues to be a fascinating and useful area of
research.1 We describe herein some novel results of an
exploratory study of the oxidation of various olefins by tert-
butylhydroperoxide in the presence of catalytic amounts of
palladium(II) acetate or trifluoroacetate. Two different reac-
tion pathways have been observed using a mixture of the
catalytic Pd(II) salt, t-BuOOH, and olefin in CH2Cl2 at 0-25
°C in the presence of catalytic amounts of K2CO3: (1) allylic
peroxy ether formation and (2) epoxidation, as shown in
Scheme 1. In terms of conditions, product, and reaction
A variety of olefins have been converted to epoxides
(Scheme 1, path A) using 5 equiv of t-BuOOH, 10 mol %
Pd(OAc)2, or Pd(OAc)2‚BINAP complex in the presence of
25 mol % K2CO3 in CH2Cl2 at 0 °C, as summarized in Table
1. Both carboxylate ligands appear to be displaced from PdX2
1
by tert-butylperoxy ligands as shown by H NMR analysis
and also mass spectral analysis, which indicated the species
Pd(OOt-Bu)2‚2C5D5N after coordination with pyridine-d5. At
room temperature the mixture of catalyst and t-BuOOH gives
rise to liberation of O2, indicative of the formation of the
peroxy radical t-Bu-OO•, which can dimerize to the unstable
di-tert-butyltetraoxide.3,4 The simplest and clearest explana-
tion for the epoxidation reaction is the free radical chain
process shown in Scheme 2 for (Z)-stilbene f trans-stilbene
oxide. The formation of epoxides by the cyclization of
Scheme 1
(1) For some recent examples, see: (a) Andrus, M. B.; Lashley, J. C.
Tetrahedron 2002, 58, 845. (b) Eames, J.; Watkinson, M. Angew. Chem.,
Int. Ed. 2001, 40, 3567. (c) Chen, H.; Hartwig, J. F. Angew. Chem., Int.
Ed. Engl. 1999, 38, 3391. (d) Espino, C. G.; Wehn, P. M.; Chow, J.; DuBois,
J. J. Am. Chem. Soc. 2001, 123, 6935. (e) Kohmura, Y.; Kawasaki, K.-i.;
Katsuki, T. Synlett 1997, 1456.
(2) Heumann, A.; Reglier, M.; Waegell, B. Angew. Chem., Int. Ed. Engl.
1982, 21, 366. (b) Heumann, A.; Akermark, B. Angew. Chem., Int. Ed.
Engl. 1984, 23, 453. (c) McMurry, J. E.; Korovsky, P. Tetrahedron Lett.
1984, 25, 4187. (d) Backvall, J.-E. Acc. Chem. Res. 1983, 16, 335.
(3) See: (a) Bartlett, P. D.; Gu¨nther, P. J. Am. Chem. Soc. 1966, 88,
3288. (b) Bartlett, P. D.; Guaraldi, G. J. Am. Chem. Soc. 1967, 89, 4799.
pathway, the new allylic peroxidation is decidedly different
from the well-known Pd(OAc)2-catalyzed allylic oxidation
of olefins to form allylic acetates.2
10.1021/ol0262340 CCC: $22.00 © 2002 American Chemical Society
Published on Web 07/09/2002