LETTER
1431
Rhodium- and Iridium-Catalyzed Allylation of Electron-Rich Arenes with
Allyl Tosylate
Allylationof
Elect
a
r
on-RichA
o
renes fumi Tsukada,* Yasushige Yagura, Tetsuo Sato, Yoshio Inoue
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
Fax +81(22)2175873; E-mail: tsukada@aporg.che.tohoku.ac.jp
Received 20 March 2003
tution reactions. Although by using allyl mesylate as an
allylating reagent a trace amount of 2a was obtained (en-
try 2), the reaction with other allylic compounds such as
allyl acetate, allyl trifluoroacetate, allyl methyl carbonate,
allyl alcohol, allyl iodide, and allyl bromide did not give
any product. More electron-rich arenes, such as 1,2,3,5-
tetramethylbenzene (1b) and pentamethylbenzene (1c),
reacted with allyl tosylate, affording the allylated product
2b and 2c in good yields, respectively (entries 3 and 4).
However, no reaction occurred when xylene, 1,2,3-trime-
thylbenzene, 1,2,4-trimethylbenzene, and 1,2,4,5-tetra-
methylbenzene were used. These results indicate that the
allylation occurs only on an aromatic carbon that has more
than three methyl substituents on its ortho- and para-
positions. Crotyl tosylate also reacted with 1a, giving the
linear product 2d selectively (entry 5).
Abstract: The allylation of electron-rich arenes with allyl tosylate
proceeded at 0 °C in the presence of [Rh(nbd)(CH3CN)2]PF6. Vari-
ous oxygenated arenes were allylated with high para-selectivity in
almost all cases. Especially in the reaction of anisoles, the tendency
was remarkable.
Key words: allylations, arenes, catalysis, iridium, rhodium
Allyl- or prenyl-substituted arenes, especially phenolic
compounds, constitute an important class of biologically
active natural products and drugs.1 Aromatic electrophilic
substitution with alkyl halides, namely the Friedel–Crafts
reaction, is one of the most simple and general methods
for the synthesis of substituted arenes.2,3 However, in the
reaction using allyl halide or allyl alcohol, a classical met-
al halide catalyst such as AlCl3 brings about the addition
to the double bond and/or various side reactions.2,3 Thus,
the yield of the desired allylated product is generally
low. In contrast, scandium(III) triflate4 or transition
metal complexes such as Pd(OAc)2/dppf5 and
[(C5Me5)RuCl(SPri)2Ru(OH2)-(C5Me5)]OTf6 were re-
cently reported to catalyze the allylation with allylic alco-
hols to afford allylated products in high yields without the
side reactions. Molybdenum and tungsten complexes are
also efficient for the allylation of arenes with allylic es-
ters,7 and, furthermore, the allylation catalyzed by
[Mo(CO)4Br2]2 or (acac)2Mo(SbF6)2 with allylic com-
pounds such as allylic esters and alcohols proceeds even
at room temperature.8 In our previous study utilizing allyl
tosylate as an allylating agent,9 we found that cationic
rhodium complexes were efficient for the allylation of
alkenes with allyl tosylate.9b We report here that the allyl-
ation of electron-rich arenes with allyl tosylate proceeds
smoothly at 0 °C in the presence of rhodium or iridium
complexes.
R1
[Rh(nbd)(CH3CN)2]PF6
R3
X
+
toluene, 0 °C, 24 h
R2
R1
1a (R1 = R2 = H)
1b (R1 = Me, R2 = H)
1c (R1 = R2 = Me)
R3
R2
2a (R1 = R2 = R3 = H)
2b (R1 = Me, R2 = R3 = H)
2c (R1 = R2 = Me, R3 = H)
2d (R1 = R2 = H, R3 = Me)
Scheme 1
Since polymethyl-substituted electron-rich arenes are
reactive in the present allylation, we next examined the
reaction of electron-rich oxygenated arenes. Some of the
allylated products obtained are naturally occurring mate-
rials, and serve as perfumes, agrochemicals, and pharma-
ceuticals and their synthetic intermediates. Table 1 shows
the results of the allylation of alkoxy-substituted arenes
with allyl tosylate. The reaction of anisole (3a) was highly
selective to give estragole (4a) in 54% yield, without the
formation of o- and m-isomers (entry 1). The reaction of
arenes which have two or three methoxy groups also pro-
ceeded smoothly at 0 °C with high regioselectivity. Meth-
yl eugenol (4b) was obtained by the allylation of 1,2-
dimethoxybenzene (3b) (entry 2). 1,3-Dimethoxybenzene
(3c) and 1,3,5-trimethoxybenzene (3e) were also reacted
The reaction of mesitylene (1a) with allyl tosylate
(Scheme 1) at
0
°C in the presence of
[Rh(nbd)(CH3CN)2]PF6 (5 mol%) afforded the allylated
product 2a in 71% yield (Table 1, entry 1). Other rhodium
complexes such as [Rh(nbd)Cl]2, [Rh(nbd)2]BF4 and
RhCl(PPh3)3 were less effective, and no reaction occurred
using several palladium and molybdenum complexes,
which are known to be efficient for various allylic substi-
Synlett 2003, No. 10, Print: 05 08 2003.
Art Id.1437-2096,E;2003,0,10,1431,1434,ftx,en;U08703ST.pdf.
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