SCHEME 1
SCHEME 2
Ha lid e-F r ee Deh yd r a tive Allyla tion Usin g
Allylic Alcoh ols P r om oted by a
P a lla d iu m -Tr ip h en yl P h osp h ite Ca ta lyst
Yoshihito Kayaki, Takashi Koda, and Takao Ikariya*
PRESTO, J apan Science and Technology Agency, and
Graduate School of Science and Engineering and Frontier
Collaborative Research Center, Tokyo Institute of
Technology, O-okayama, Meguro-ku, Tokyo 152-8552, J apan
leaving groups.11 Successful application of a halide-free
process involving the C-O bond cleavage of allylic
alcohols without any activating reagents has been more
limited.12,13 In a recent work reported by Ozawa and
Yoshifuji, η3-allylpalladium complexes bearing the unique
bidentate sp2-hybridized phosphorus ligand, diphosphin-
idenecyclobutene, proved to be capable of catalyzing C-
and N-allylations using allylic alcohols without OH-
activators.14 However, the addition of pyridine as a base
was required for the C-allylation of active methylene
compounds to enhance their nucleophilicity. Herein, we
will describe a highly efficient Pd-P(OC6H5)3 catalyst for
substitution reactions of allylic alcohols via direct C-O
bond cleavage without cocatalysts and bases, affording
allylic ethers in excellent yields.
We first examined the reactivity of 2-propene-1-ol (1,
10 mmol) with Pd catalysts (0.05 mmol) in the absence
of solvent or additives. The screening test of the Pd
catalysts revealed that a combined catalyst, Pd2(dba)3‚
CHCl3 and P(OC6H5)3, provided the best catalyst perfor-
mance with the dehydrative etherification of 1 at 80 °C
under neutral conditions (Scheme 2). As shown in Table
1, the aryl phosphite ligand P(OC6H5)3, with electron-
withdrawing character, gave a satisfactory result in the
formation of diallyl ether (2). Use of 4 equiv of the
phosphite ligand with respect to Pd was required to give
an optimum yield (entries 2-4). The use of P(CH2CH2-
CH2CH3)3 and DPPB12a,c ligands led to moderate yields
of 2, while other phosphorus ligands were ineffective. An
isolable Pd(0) complex [Pd{P(OC6H5)3}4] (3)15 was also
suitable for the dehydrative etherification with a similar
catalyst activity, whereas a Pd(II) complex, [PdCl2-
tikariya@o.cc.titech.ac.jp
Received December 4, 2003
Abstr a ct: The triphenyl phosphite-palladium complex was
found to effect catalytic substitution reactions of allylic
alcohols via a direct C-O bond cleavage. The dehydrative
etherification proceeded efficiently without any cocatalysts
and bases to give allylic ethers in good to excellent yields.
Palladium-catalyzed transformations of allylic com-
pounds represent powerful and well-established synthetic
procedures for carbon-carbon and carbon-heteroatom
bond formation, with high chemo-, regio-, and stereo-
selectivities.1 Acetates, carbonates, and related deriva-
tives of allylic alcohols have normally been used as
substrates, because the parent alcohols do not undergo
the allylic transformation due to the difficulty of the
allylic C-O bond cleavage by Pd catalysts. While it is
inevitable for the reaction of allyl halides and esters
under basic conditions to form the corresponding salt
wastes, direct utilization of allylic alcohols without any
additional promoters potentially provides economical,
technical, and environmental advantages because of the
formation of water as a coproduct derived from the
leaving OH group (Scheme 1). As an approach for
promoting Pd-catalyzed transformations of allylic alco-
hols, several researchers have demonstrated that addi-
tives such as P(C6H5)3-DEAD,2 As2O3,3 B2O3,4 BF3‚Et2O,5
10
BEt3,6 B(C6H5)3,7 SnCl2,8 Ti(OiPr)4,9 and CO2 can acti-
vate and/or convert the OH moiety into more labile
* Corresponding author. Phone: +81 3 5734 2636. Fax: +81 3 5734
2637.
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10.1021/jo030370g CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/04/2004
J . Org. Chem. 2004, 69, 2595-2597
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