C O MMU N I C A T I O N S
Table 2. Allylic Oxidation of Terminal Olefins to (E)-Allylic
acetates in preparatively useful yields (Table 2). The high selectivity,
functional group compatibility, and directness of this method make
it a powerful alternative to C-C bond forming procedures that
require multistep routes for accessing the majority of products in
Table 2.6
Acetatesa
Consistent with a mechanism involving π-allyl intermediates,
stoichiometric formation of bis[chloro(1,2,3-trihapto-1-decene)-
palladium(II)]2d and subsequent exposure of it to our DMSO
acetoxylation conditions generated the linear and branched allylic
acetates observed in the catalytic reaction (SI). Regioisomeric ratios
7
2
for both the DMSO and bis-sulfoxide catalytic Pd(OAc) acetoxy-
8
lation systems decrease slowly over the course of the reaction.
This suggests a mechanism involving sulfoxide ligand-directed
regioselective acetate substitution of a π-allyl intermediate with
8,9
background Pd(II)-catalyzed allylic acetate isomerization. Inves-
tigation of the reaction mechanism and studies toward an under-
standing of the role of sulfoxide ligation on selectivity are in
progress.
Acknowledgment. M.S.C. gratefully acknowledges the Under-
graduate Harvard College Research Program for a summer fellow-
ship. M.C.W. gratefully acknowledges the Camille and Henry
Dreyfus Foundation and Harvard University for financial support.
We are grateful to a reviewer for suggesting the stoichiometric
π-allyl experiment and to Dr. G. Dudek and Ms. Q. Liao for mass
spectral analyses.
Supporting Information Available: General experimental proce-
dures. This material is available free of charge via the Internet at http://
pubs.acs.org.
References
(
1) Pd(II)/AcOH: (a) Hansson, S.; Heumann, A.; Rein, T.; A° kermark, B. J.
Org. Chem. 1990, 55, 975. (b) Heumann, A.; Reglier, M.; Waegell, B.
Angew. Chem., Int. Ed. Engl. 1982, 21, 366. (c) Heumann, A.; A° kermark,
B. Angew. Chem., Int. Ed. Engl. 1984, 23, 453. (d) McMurry, J. E.;
Kocovsky, P. Tetrahedron Lett. 1984, 25, 4187. (e) A° kermark, B.; Larsson,
E. M.; Oslob, J. D. J. Org. Chem. 1994, 59, 5729. (f) Macsari, I.; Szabo,
a
2
K. J. Tetrahedron Lett. 1998, 39, 6345. SeO /t-BuOOH: (g) Umbreit,
All data reported ([L:B], [E:Z] ratios, yields) based on an average of
M. A.; Sharpless, K. B. J. Am. Chem. Soc. 1977, 99, 5526. Cu(I)/tert-
butyl perbenzoate: (h) Andrus, M. B.; Lashley, J. C. Tetrahedron 2002,
two runs. Minor peaks consistent with diene byproducts were detected by
1
b
c
H NMR analysis of the crude. 10 mol % of Pd(TFA)2. Ratio based on
GC analysis of crude. Not corrected for small response factor variations.
58, 845.
(2) (a) Grennberg, H.; Backvall, J.-E. Chem. Eur. J. 1998, 4, 1083. (b) Wolfe,
S.; Campbell, P. G. C. J. Am. Chem. Soc. 1971, 93, 1497, 1499. (c)
Kitching, W.; Rappoport, Z.; Winstein, S.; Young, W. G. J. Am. Chem.
Soc. 1966, 88, 2054. (d) Trost, B. M.; Metzner, P. J. J. Am. Chem. Soc.
d
e
Ratio based on 1H NMR analysis of crude. Isolated yields after
chromatography from reactions carried out on a 1.0 mmol scale (0.17 M).
1980, 102, 3572.
(
3) Pd(II)/DMSO/O : (a) Steinhoff, B. A.; Fix, S. R.; Stahl, S. S. J. Am.
2
oxidation versus Wacker oxidation chemistry and control the
regioselectivity in the C-H oxidation products. Further studies will
Chem. Soc. 2002, 124, 766. (b) Grennberg, H.; Gogoll, A.; Backvall, J.-
E. J. Org. Chem. 1991, 56, 5808.
2
(4) A similar observation in a stoichiometric Pd(OAc) system, ref 2c.
probe the effects of steric and electronic tuning of the C
2
-symmetric,
(5) S-Pd coordination mode is tentatively assigned based on other Pd(II)
bis-sulfoxide complexes. Pettinari, C.; Pellei, M.; Cavicchio, G. Cru-
cianelli, M.; Panzeri, W.; Colapietro, M.; Cassetta, A. Organometallics
1999, 18, 555.
bis-sulfoxide ligand framework on the reactivity and selectivity of
the C-H oxidation reaction and on its amenability to asymmetric
catalysis.
Because (E)-allylic acetates and their corresponding alcohols are
valuable synthetic intermediates, we explored the generality and
synthetic utility of the DMSO-promoted C-H oxidation reaction
(
(
(
6) For a standard HWE-based 5-6 step synthetic route toward functionalized
(
E)-allylic acetates, see: (a) Trost, B. M.; Verhoeven, T. R. J. Am. Chem.
Soc. 1980, 102, 4743. Cross-metathesis has been used to directly synthesize
entry 10 in 51% yield: (b) Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.;
Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 11360.
3
7) Neutral, strongly coordinating Pd(II) ligands (e.g., DMSO, PPh ) have
been used to activate stoichiometric π-allyl chloride complexes toward
alkylation: (a) Collins, D. J.; Jackson, W. R.; Timms, R. N. Tetrahedron
Lett. 1976, 495. (b) Trost, B. M.; Fullerton, T. J. J. Am. Chem. Soc. 1973,
95, 292. (c) Trost, B. M. Acc. Chem. Res. 1980, 13, 385.
(
Table 2). Evaluation of reaction parameters (Tables S1-S8)
indicated that the reaction conditions Pd(OAc) (10 mol %)/BQ (2
equiv)/4 Å MS/DMSO:AcOH (1:1, v/v) at 40 °C are presently
optimal. Palladium(II) trifluoroacetate [Pd(TFA) ] gave similar
results in the presence of 4 Å MS and, in general, the addition of
Å MS increased formation of linear (E)-allylic acetate (Tables
2
8) Table 1, entry 2 (w/MS): 24 h, [L:B] ) 34:1; 72 h, [L:B] ) 11:1. Table
2
1
, entry 3: 24 h, [L:B] ) 1:10; 72 h, [L:B] ) 1:7 (Table 2 and eqs 2, 3
see SI). Submission of regioisomerically pure (E)-acetic acid dec-2-enyl
ester to the DMSO reaction conditions resulted in the same trend.
Overman, L. E.; Knoll, F. M. Tetrahedron Lett. 1979, 4, 321.
4
S1, S2). Notably, these conditions are operationally simple and
tolerant of a wide range of functionality. Benzyl and silyl ether-,
ketal-, ester-, carbamate-, and amide-functionalized monosubstituted
olefins underwent direct oxidation with excellent regio- and
stereoselectivities to generate the corresponding linear (E)-allylic
(9) An alternative mechanism involving anti-Markovnikov oxypalladation/
â-hydride elimination/Pd-H isomerization to the linear (E)-allylic acetate
followed by Pd(II)-mediated allylic isomerization to the branched acetate
is not consistent with the observed trend of progressively decreased
branched:linear ratios over the course of the reaction with catalyst 1.
JA039107N
J. AM. CHEM. SOC.
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