ORGANIC
LETTERS
2010
Vol. 12, No. 4
824-827
Allylic Oxidations of Terminal Olefins
Using a Palladium Thioether Catalyst
William H. Henderson, Christopher T. Check, Nicolas Proust, and James
P. Stambuli*
Department of Chemistry, The Ohio State UniVersity, 100 West 18th AVenue,
Columbus, Ohio 43210
Received December 17, 2009
ABSTRACT
A palladium catalyst that converts terminal olefins to linear allylic acetates at lower catalyst loadings and faster reaction times than current
systems is reported. This reaction can be conducted using benzoquinone as the oxidizing agent or catalytic amounts of copper and hydroquinone
under one atmosphere of oxygen. Preliminary reactivity studies of π-allylpalladium complexes under our reaction conditions do not provide
results similar to those obtained in the catalytic reaction, which may suggest an alternative reaction pathway. The palladium catalyst is ligated
by an aryloxyalkyl aryl sulfide, which is identified as a new ligand for homogeneous catalysis.
The functionalization of allylic C-H bonds via selective
oxidation reactions has the potential to greatly impact the
synthesis of complex molecules.1 Traditionally, allylic oxida-
tions have been mediated by selenium2a and copper,2b,c but
functional group tolerance and low selectivities are prob-
lematic for these metals. Other metals such as mercury2d and
rhodium2e have also been investigated. Over four decades
ago, a stoichiometric Pd(OAc)2-promoted oxidation of the
allylic C-H bond of 1-butene in neat AcOH was reported
to give the corresponding vinyl acetate as the major product
along with 9% of the linear allylic acetate.3 However, the
addition of DMSO provided an 8-fold increase of linear
allylic acetate. Although much work has been done on allylic
oxidations of disubstituted olefins since these findings,4 few
selective methods for allylic oxidation reactions of terminal
olefins to allylic acetates have been reported.5,6 White and
co-workers showed that palladium(II) complexes ligated by
sulfoxides catalyzed the conversion of terminal alkenes to
either linear or branched allylic acetates with very good
selectivities.6 However, some of the challenges that remain
include high catalyst loadings, long reaction times, and the
requirement of excess benzoquinone (BQ). Herein, we
present a unique aryloxyalkyl aryl sulfide palladium catalyst
that converts terminal olefins to linear allylic acetates in good
yields and regioselectivities. This allylic oxidation reaction
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10.1021/ol902905w 2010 American Chemical Society
Published on Web 01/25/2010