Rhenium-catalyzed allylation of C-H bonds of benzoic and acrylic acids

Article abstract of DOI:10.1039/c1cc12359a

We have succeeded in the allylation of aromatic and olefinic C-H bonds of benzoic and acrylic acids using a rhenium catalyst, Re₂(CO) ₁₀. In this reaction, isomerization of the introduced allyl group to the 1-propenyl group did not occur.

Full text of DOI:10.1039/c1cc12359a

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Rhenium-catalyzed allylation of C–H bonds of benzoic and acrylic acidsw
Yoichiro Kuninobu,* Kazuhiro Ohta and Kazuhiko Takai*
Received 22nd April 2011, Accepted 3rd August 2011
DOI: 10.1039/c1cc12359a
We have succeeded in the allylation of aromatic and olefinic
C–H bonds of benzoic and acrylic acids using a rhenium
catalyst, Re2(CO)10. In this reaction, isomerization of the
introduced allyl group to the 1-propenyl group did not occur.
In this reaction, neither the isomerization of the terminal
olefin moiety of 2a or 3a to the internal position, nor the
decarboxylation of 2a occurred. To increase the selectivity of
2a by deallylation of the ester moiety of 3a, several trans-
formations have been investigated. As a result, the rhenium-
catalyzed Tsuji–Trost type reaction was found to be effective
for the deallylation without isomerization of the olefinic
moiety.11 After the allylation, by the treatment of the reaction
mixture with 3-methyl-2,4-pentanedione (4), deallylation of
the ester moiety of 3a occurred, and the yield of 2a was
improved to 66% [eqn (1)]. In this step, a p-allyl rhenium
intermediate must be formed from allyl ester 3a and the
rhenium catalyst.
The allylic alkylation of aromatic and olefinic compounds is one
of the most useful methods to synthesize allylated aromatic
compounds and 1,4-dienes, respectively. Among these methods,
direct allylation at carbon–hydrogen (C–H) bonds is an efficient
method to introduce allyl groups into organic molecules. There-
fore, there have been many reports on such transformations.
Typical examples are the Friedel–Crafts reaction of aromatic
compounds1 and the Claisen rearrangement ([3,3]-sigmatropic
rearrangement) of allyl phenyl ethers and allyl vinyl ethers.2
In the Friedel–Crafts reaction, there are several problems: the
introduction of two or more allyl groups, low regio- and
stereoselectivity, and narrow scope of substrates (limited to
electron-rich and multisubstituted aromatic compounds). To
promote regioselective allylation, the Claisen rearrangement is
more efficient and reliable because the reaction proceeds via a
six-membered transition state. In addition, allylation occurs
with both aromatic and olefinic compounds. Recently, trans-
formations via C–H bond activation have received much
attention because of their efficiency.3 However, there have
been only a few examples of allylic alkylation via C–H bond
activation.4,5 In these reactions, the products are obtained as
a mixture of terminal and isomerized internal olefins and
stereoisomers. We report herein the regioselective allylation
of benzoic and acrylic acids using a rhenium catalyst, Re2(CO)10.6
In this reaction, allylation occurs only at the ortho-position of
benzoic acids and at the cis-b-position of acrylic acids.
ð1Þ
In eqn (1), one reason for the low yield of 2a is the
formation of a carboxylic acid by deallylation of 1a under
the reaction conditions. Therefore, to increase the yield of 2a,
allyl acetate (5) was added as an allyl source to regenerate 1a
from the decomposed carboxylic acid, and the catalytic
amount of Re2(CO)10 was increased. As a result, the yield of
2a increased to 76% (Table 1, entry 1). Next, we investigated
the scope and limitations of benzoates and acrylates (Table 1,
entries 2–12). A benzoate with an electron-withdrawing or
-donating group at the R1 position, 1b and 1c, promoted
allylation at the ortho-position of the hydroxycarbonyl group,
and 2-allyl benzoic acids 2b and 2c were obtained in 60% and
25% yields after deallylation of the allyl esters of 3b and 3c
(entries 2 and 3). In entry 3, 2-methoxybenzoic acid was
formed in ca. 70% yield. The corresponding 2-allyl benzoic
acids 2d and 2e were produced from allyl benzoates 1d and 1e
without loss of the halogen atom (entries 4 and 5). A mixture
of mono- and di-allylated products 2f and 2f0 (or 2h and 2h0)
was formed using a benzoate without a substituent at the
aromatic ring, 1f (or a benzoate with a substituent at the
para-position, 1h) (entries 6 and 8). The allylation reaction
proceeded with high regioselectively when allyl 3-methyl-
benzoate (1g) was employed as a substrate (entry 7). The
corresponding allylated product 2i was produced using a
By the treatment of allyl 2-methylbenzoate (1a) with a
catalytic amount of a rhenium catalyst, Re2(CO)10, in 1,2-
dichloroethane at 135 1C for 24 h, allylation proceeded at the
ortho-position of 1a and 2-allyl-6-methylbenzoic acid (2a) and
allyl 2-allyl-6-methylbenzoate (3a), which is an allyl ester of 2a,
were formed in 58% and 15% yields, respectively [eqn (1)].7–10
Division of Chemistry and Biochemistry, Graduate School of Natural
Science and Technology, Okayama University, Tsushima, Kita-ku,
Okayama 700-8530, Japan. E-mail: kuninobu@cc.okayama-u.ac.jp,
ktakai@cc.okayama-u.ac.jp; Fax: +81-86-251-8094;
Tel: +81-86-251-8095
w Electronic supplementary information (ESI) available: The general
procedure, product characterization data and 1H and 13C NMR
spectra of 2a–i, 3a, 7a–c, and 9, and the results of deuterium labeling
experiments. See DOI: 10.1039/c1cc12359a
c
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Table 1 Reactions of several benzoates 1 and acrylates 6a
stereoselectively. Rearrangement of the terminal double bond
leading to a conjugate dienoic acid was not observed.
ð3Þ
To elucidate the reaction mechanism, the following reactions
were carried out. Treatment of deuterated benzoic acid 12-d
with D2O in the presence of Re2(CO)10 gave ortho-deuterated
benzoic acid 12-d0 in 69% yield [eqn (4)] (see the ESI, refs
S1–S5). In this reaction, the deuteration occurred only at
the ortho-position. When using deuterated methacrylic acid
(10-d), deuteration also proceeded at the cis-b-position of the
olefinic moiety, and only a single stereoisomer 10-d0 was
generated [eqn (4)] (see the ESI, ref S6). These results indicate
that aromatic and olefinic C–H bond activation occurs at only
the ortho- and cis-b-positions of benzoates and acrylates,
respectively.
ð4Þ
A reaction starting from 1,1-dideuterated allyl benzoate
1a-d was also examined. After treatment of 1a-d with a
catalytic amount of Re2(CO)10 for 6 h, deuterated 2-allyl
benzoate 2a-d was formed in 3% yield and 1a-d0 was recovered
in 70% yield [see ESIw, eqn (S1)]. In the starting substrate
1a-d, some deuterium atoms were transferred to the terminal
olefinic position. This result indicates that the allyl group of
1a-d is isomerized via p-allyl rhenium intermediate A as shown
in Scheme 1. In the product 2a-d, both Ha and [Hb + Hc]
positions were 45% and 55% deuterated, respectively. This
result supports the existence of the second p-allyl rhenium
intermediate B (Scheme 1) in the reaction pathway, and that
the scrambling rate via intermediate B is faster than that via
intermediate A. After 24 h, deuterated 2-allyl benzoate 2a-d
and its allyl ester 3a-d were obtained in 50% and 9% yields,
respectively, and starting substrate 1a-d disappeared
[eqn (S1)w]. In this reaction, the deuterium atoms were intro-
duced into both the terminal and allylic positions of the allyl
group of the products 2a-d and 3a-d. This result and that
obtained in the deallylation shown in eqn (1) also indicate the
existence of p-allyl rhenium intermediates A and B.
a
b
5 (1.0 equiv). Isolated yield. Yields determined by 1H NMR are
c
d
reported in parentheses. First step: 150 1C, 36 h. Allyl acetate (5)
was not added. 5 (1.0 equiv) was added after 18 h. 150 1C.
e
f
heteroaromatic compound 1i (entry 9). By the reaction of
cyclic or acyclic allyl acrylates, 6a–c, the corresponding ally-
lated products 7a–c were provided (entries 10-12).12 In these
reactions, Z/E isomerization of the olefin moiety of acrylic
acid did not occur.
Next, 3-buten-2-yl 2-methylbenzoate (8), which has a
methyl group at the allylic position, was treated with a
catalytic amount of Re2(CO)10 [eqn (2)]. Allylation proceeded
at the ortho-position of the aromatic ring, and (E)-2-crotyl
2-methylbenzoic acid (9) was formed in low yield.13 However,
the olefinic (Z) stereoisomer was not formed at all.
(2)
Kinetic isotope effect (KIE) was measured to determine
whether the step of C–H bond activation is a rate-determining
step or not. The obtained KIE value was 2.1 (see the ESIw,
eqn (S2) and ref S7), which indicates that C–H bond activation
is the rate-determining step.
Allylation of an olefinic compound also proceeded by
the reactions between acrylic acid 10 and allyl alcohol (11)
in the presence of Re2(CO)10 [eqn (3)].14 After the treatment
of the reaction mixture with 3-methyl-2,4-pentanedione (4),
cis-b-substituted allylated product 7c was produced regio- and
As a result of the above experiments, the proposed mechanism
for the allylation is as follows (Scheme 1 (see the ESI, ref S8)):
(1) coordination of an allyl benzoate (or acrylate) to the
rhenium center;15,16 (2) oxidative addition of the allyl benzoate
c
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8 Investigation of several solvents: neat: 2a, 8%, 3a, 3%; octane: 2a,
30%, 3a, 17%; toluene: 2a, 27%, 3a, 24%. No reaction: 1,4-dioxane,
THF, DMSO, DMF.
9 We have reported on rhenium-catalyzed transformations via aro-
matic C–H bond activation. See: (a) Y. Kuninobu, A. Kawata and
K. Takai, J. Am. Chem. Soc., 2005, 127, 13498; (b) Y. Kuninobu,
Y. Nishina, M. Shouho and K. Takai, Angew. Chem., Int. Ed.,
2006, 45, 2766; (c) Y. Kuninobu, P. Yu and K. Takai, Org. Lett.,
2010, 12, 4274; (d) Y. Kuninobu, T. Nakahara, P. Yu and
K. Takai, J. Organomet. Chem., 2011, 696, 348.
10 For examples of the synthesis of 2-allylbenzoate by cross-coupling
reaction, see: (a) P. H. Lee, S.-Y. Sung and K. Lee, Org. Lett.,
2001, 3, 3201; (b) S. E. Denmark and N. S. Wernwe, J. Am. Chem.
Soc., 2008, 130, 16382.
11 We have already reported rhenium-catalyzed Tsuji–Trost type
reaction: T. Ureshino, S. S. Yudha, Y. Kuninobu, K. Takai, The
88th Annual Meeting of the Chemical Society of Japan, 3H1-42.
12 For transformations via olefinic C-H bond activation, see:
(a) F. Kakiuchi, Y. Tanaka, T. Satoh, N. Chatani and S. Murai,
Chem. Lett., 1995, 24, 679; (b) B. M. Trost, K. Imi and
I. W. Davies, J. Am. Chem. Soc., 1995, 117, 5371;
(c) F. Kakiuchi, T. Satoh, K. Igi, N. Chatani and S. Murai, Chem.
Lett., 2001, 30, 386; (d) Y.-G. Lim, J.-B. Kang, K. Lee and
Y. H. Kim, Heteroatom Chem., 2002, 13, 346; (e) D. A. Colby,
R. G. Bergman and J. A. Ellman, J. Am. Chem. Soc., 2006,
128, 5604; (f) Y. Kuninobu, Y. Nishina, T. Matsuki and
K. Takai, J. Am. Chem. Soc., 2008, 130, 14062;
(g) Y. Kuninobu, Y. Fujii, T. Matsuki, Y. Nishima and
K. Takai, Org. Lett., 2009, 11, 2711 and references therein.
13 In this reaction, 2-methylbenzoic acid was also formed. In addi-
tion, the yield of 9 was not improved by adding allylic acetate 5.
14 For carboxylic acid-directed regioselective C–H bond transforma-
tions, see: (a) D.-H. Wang, K. M. Engle and J.-Q. Yu, Science,
2010, 327, 315; (b) K. M. Engle, B.-F. Shi, D.-H. Wang and
J.-Q. Yu, Angew. Chem., Int. Ed., 2010, 49, 6169.
15 There have been some reports on a transformation via C–H bond
activation using a directing group in a bidentate manner. See: (a) B.
V. S. Reddy, L. R. Reddy and E. J. Corey, Org. Lett., 2006,
8, 3391; (b) F.-R. Gou, X.-C. Wang, P.-F. Huo, H.-P. Bi,
Z.-H. Guan and Y.-M. Liang, Org. Lett., 2009, 11, 5726;
(c) D. Shavashov and O. Daugulis, J. Am. Chem. Soc., 2010,
132, 3965; (d) N. Hasegawa, V. Charra, S. Inoue, Y. Fukumoto
and N. Chatani, J. Am. Chem. Soc., 2011, 133, 8070 and references
therein.
Scheme 1 Proposed mechanism for allylation.
(or acrylate) to the rhenium center (C–H bond activation); (3)
formation of an allyl rhenium intermediate; and (4) reductive
elimination to give the allylated product and regenerate the
rhenium catalyst. In this mechanism, p-allyl rhenium inter-
mediates A and B must be formed as shown in Scheme 1.17,18
Another possible pathway is that p-allyl rhenium intermediate
A is converted directly to B via C–H bond activation.
In conclusion, we have succeeded in the allylation of
aromatic and olefinic C–H bonds using a rhenium complex,
Re2(CO)10, as a catalyst. The reaction occurs at the ortho-
position of benzoates and the cis-b-position of acrylates regio-
and stereoselectively. In addition, the olefin moiety of the
products was not isomerized. This reaction is advantageous
over both the Friedel–Crafts reaction and Claisen rearrange-
ment because it can achieve regioselective allylation of benzoic
and acrylic acids. We hope that this reaction will provide
useful insight into C–H bond transformations.
This work was partially supported by the Ministry of
Education, Culture, Sports, Science, and Technology of Japan.
Notes and references
16 In this reaction, the hydroxycarbonyl group works as a directing
group. There are some examples using hydroxycarbonyl as a
directing group to promote regioselective C–H functionalizations.
See: (a) H. A. Chiong, Q.-N. Pham and O. Daugulis, J. Am. Chem.
Soc., 2007, 129, 9879; (b) M. Nakano, H. Tsurugi, T. Satoh and
M. Miura, Org. Lett., 2008, 10, 1851; (c) R. Giri and J.-Q. Yu,
J. Am. Chem. Soc., 2008, 130, 14082; (d) S. Mochida, K. Hirano,
T. Satoh and M. Miura, Org. Lett., 2010, 12, 5776. See also,
ref. 16a.
17 If the rate of the equilibrium between the p-allyl rhenium inter-
mediate A and the two s-allyl rhenium intermediates is much faster
than the rate of C–H bond activation and the following steps, there
is a possibility that intermediate B does not exist. In the experiment
run for 6 h, the ratio of hydrogen atoms in 1a-d0 (Hj/Hk + Hl =
0.18/1.82 = 0.099) was much smaller than the ratio of hydrogen
atoms in 2a-d (Ha/Hb + Hc = 1.10/0.90 = 1.2). This result
indicates that another scrambling step must exist after the formation
of p-allyl rhenium intermediate A. Therefore, we are tempted to
assume the existence of intermediate B.
1 For examples, see: (a) J.-H. Min, J.-S. Lee, J.-D. Yang and S. Koo,
J. Org. Chem., 2003, 68, 7925; (b) M. Niggemann and M. J. Meel,
Angew. Chem., Int. Ed., 2010, 49, 3684.
2 (a) L. Claisen, Ber. Deutsch. Chem. Ges., 1913, 45, 3157; (b) L. Claisen
and O. Eisleb, Justus Liebigs Ann. Chem., 1914, 401, 21.
3 For reviews, see: (a) F. Kakiuchi and S. Murai, Top. Organomet.
Chem., 1999, 3, 47; (b) Y. Guari, S. Sabo-Etienne and B. Chaudret,
Eur. J. Inorg. Chem., 1999, 1047; (c) G. Dyker, Angew. Chem., Int.
Ed., 1999, 38, 1698; (d) V. Ritleng, C. Sirlin and M. Pfeffer, Chem.
Rev., 2002, 102, 1731; (e) F. Kakiuchi and T. Kochi, Synthesis, 2008,
3013; (f) D. A. Colby, R. G. Bergman and J. A. Ellman, Chem. Rev.,
2010, 110, 624; (g) T. W. Lyons and M. S. Sanford, Chem. Rev.,
2010, 110, 1147; (h) T. Satoh and M. Miura, Synthesis, 2010, 3395.
4 (a) S. Oi, Y. Tanaka and Y. Inoue, Organometallics, 2006,
25, 4773; (b) K. Cheng, B. Yao, J. Zhao and Y. Zhang, Org. Lett.,
2008, 10, 5309; (c) Y. J. Zhang, E. Skucas and M. J. Krische, Org.
Lett., 2009, 11, 4248.
5 For a recent example of a review on transition metal-catalyzed
decarboxylative allylation, see: J. D. Weaver, A. Recio III,
A. J. Grenning and J. A. Tunge, Chem. Rev., 2011, 111, 1846.
6 There has been a recent review on rhenium-catalyzed reactions.
See, Y. Kuninobu and K. Takai, Chem. Rev., 2011, 111, 1938.
7 Investigation of several transition metal complexes: ReBr(CO)5: 2a,
12%, 3a, 6%; [HRe(CO)4]n: 2a, 46%, 3a, 6%. No reaction: Cr(CO)6,
Mo(CO)6, W(CO)6, Mn2(CO)10, MnBr(CO)5, [ReBr(CO)3(thf)]2,
Fe2(CO)9, Fe3(CO)12, Ru3(CO)12, RuH2(CO)(PPh3)3, [CpRu(PPh3)3-
(MeCN)2]PF6, Co2(CO)8, Rh4(CO)12, RhCl(PPh3)3, Ir4(CO)12, AuCl,
PtCl2.
18 There have been several reports on p-allyl rhenium species. See:
(a) B. J. Brisdon, D. A. Edwards and J. W. White, J. Organomet.
Chem., 1979, 175, 113; (b) R. J. Batchelor, F. W. B. Einstein,
R. H. Jones, J.-M. Zhuang and D. Sutton, J. Am. Chem. Soc.,
1989, 111, 3468; (c) G. S. Bodner, K. Emerson, R. D. Larsen and
J. A. Gladysz, Organometallics, 1989, 8, 2399; (d) C. P. Casey and
C. S. Yi, Organometallics, 1990, 9, 2413; (e) W. A. Herrmann,
F. E. Kuhn, C. C. Romao and H. T. Huy, J. Organomet. Chem.,
¨
1994, 481, 227.
c
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Chem. Commun., 2011, 47, 10791–10793 10793