Rhodium-catalyzed allyl transfer from homoallyl alcohols to acrylate esters via retro-allylation

Article abstract of DOI:10.1016/j.tetlet.2007.04.039

Retro-allylation of homoallyl alcohols by rhodium catalysts occurs to generate allylrhodium species. Insertion of acrylate esters to the allylrhodiums proceeds to give the corresponding 2,5-hexadienoate esters in situ. Subsequent isomerization or iterativ

Full text of DOI:10.1016/j.tetlet.2007.04.039

Tetrahedron Letters 48 (2007) 4003–4005
Rhodium-catalyzed allyl transfer from homoallyl alcohols
to acrylate esters via retro-allylation
Minsul Jang, Sayuri Hayashi, Koji Hirano, Hideki Yorimitsu* and Koichiro Oshima*
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto-daigaku Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan
Received 22 March 2007; revised 3 April 2007; accepted 6 April 2007
Available online 14 April 2007
Abstract—Retro-allylation of homoallyl alcohols by rhodium catalysts occurs to generate allylrhodium species. Insertion of acrylate
esters to the allylrhodiums proceeds to give the corresponding 2,5-hexadienoate esters in situ. Subsequent isomerization or iterative
1,4-addition takes place in the same pots to furnish the corresponding 2,4-hexadienoate esters or triesters in good yields.
Ó 2007 Elsevier Ltd. All rights reserved.
Metal-mediated retro-allylation of homoallyl alcohols is
an interesting method for the generation of allylmetals,
which proceeds through a carbon–carbon bond cleavage
process. Our group1 and others2 reported allyl transfer
from homoallyl alcohols to aldehydes, ketones, organic
halides, and alkynes via retro-allylation. However, allyl
transfer to alkenes has not been explored. Recently, we
have found that the retro-allylation system could be
applicable to rhodium catalysis and have achieved
catalytic allyl transfer from homoallyl alcohols to
aldehydes.3 Herein, we wish to describe rhodium-cata-
lyzed allyl transfer from homoallyl alcohols to activated
alkenes, acrylate esters.
substitution at the oxygenated carbon of homoallyl
alcohol improved the yield to 29% (entry 2). Given that
1a is the more acidic alcohol than 1a0, the final proton-
olysis would be crucial to complete the catalytic cycle
(vide infra). According to the assumption, we screened
a variety of Brønsted acids as a mediator in the proton-
olysis step. Although benzoic acid suppressed the reac-
tion completely (entry 3), phenol increased the yield to
37% (entry 4). The electron-withdrawing group on the
aromatic ring gave no effect on yield (entry 5). Interest-
ingly, sterically demanding 2-tert-butylphenol led to the
formation of 3aa in 48% yield (entry 6). Finally, with
5 mol % of [RhCl(cod)]2, 20 mol % of P(cC5H9)3,
30 mol % of cesium carbonate, and 20 mol % of 2-tert-
butylphenol, the desired product 3aa was obtained in
70% yield (entry 7).
Treatment of diisopropyl-substituted homoallyl alcohol
1a0 (0.5 mmol) with butyl acrylate (2a, 2.0 mmol) in the
presence of 2.5 mol % of [RhCl(cod)]2, 10 mol % of
P(cC5H9)3, and 15 mol % of cesium carbonate in
refluxing toluene (5.0 mL) for 10 h provided butyl (E)-
5-methyl-2,4-hexadienoate (3aa) in 18% yield (Table 1,
entry 1). Apparently, methallyl transfer from 1a0 to 2a
occurred albeit the yield was low. The reaction would
proceed via formation of r-methallylrhodium, which
would be in equilibrium with p-methallylrhodium, by
retro-methallylation. With the interesting preliminary
result, optimization studies were performed. Diphenyl
By using the optimized conditions, we conducted the al-
lyl transfer from homoallyl alcohols 1a–d bearing sub-
stituents at the b-position of the allyl moiety to
acrylate esters 2 (Table 2). Although the reaction of 1a
with bulky ester 2b gave a trace amount of the desired
product (entry 2), the allyl transfer to acrylamide 2c pro-
ceeded to produce 5,N,N-trimethyl-2,4-hexadienamide
(3ac) in moderate yield (entry 3). The phenyl-substituted
allyl moiety of homoallyl alcohol 1b could also be trans-
ferred to 2a to give the corresponding hexadienoate 3ba
in good yield with modest (E) selectivity (entry 4).
Methyl acrylate (2d) as well as butyl acrylate (2a) partic-
ipated in the reaction (entry 5). Electron-rich and elec-
tron-deficient substitutions on the benzene ring had
moderate influence on yield and stereoselectivity (entries
6–9).
Keywords: Allyl transfer; Allylrhodium; Carbon–carbon bond
cleavage; Retro-allylation.
*
Corresponding authors. Tel.: +81 75 383 2441; fax: +81 75 383 2438
(H.Y.); e-mail addresses: yori@orgrxn.mbox.media.kyoto-u.ac.jp;
oshima@orgrxn.mbox.media.kyoto-u.ac.jp
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.04.039

4004
M. Jang et al. / Tetrahedron Letters 48 (2007) 4003–4005
Table 1. Optimization for methallyl transfer from 1a to 2a via retro-
methallylation
Table 3. Rhodium-catalyzed allyl transfer from homoallyl alcohols 4
to acrylate esters 2
[RhCl(cod)]2 (5 mol %)
P(cC5H9)3 (20 mol %)
Cs2CO3 (30 mol %)
[RhCl(cod)]2 (2.5 mol %)
P(cC5H9)3 (10 mol %)
Cs2CO3 (15 mol %)
OH
OH
O
O
2-tert-butylphenol (20 mol %)
+
additive (10 mol %)
OnBu
+
Me
Me
Ph
X
Ph
toluene, reflux, 10 h
1a
2a
toluene, reflux, 10 h
Ar
4
2
X = OnBu
= OMe
2a
2d
LnRh
O
LnRh
O
2a
Ar
OR'
O
OnBu
LnRh
LnRh
2
3aa
R'O
O
OR'
Ar
Ar
Yield of 3aaa (%)
5
Entry
Additive
1b
2
3
4
5
6
7c
None
None
18
29
0
37
38
48
70
Entry
4
Ar
2a
5, Yieldb (%)
1c
2
3
4
5
6
7
8
9
4a0
4a
4a
4b
4b
4c
4c
4d
4d
Ph
Ph
Ph
2a
2a
2d
2a
2d
2a
2d
2a
2d
5aa, 35
Benzoic acid
Phenol
4-Trifluoromethylphenol
2-tert-Butylphenol
2-tert-Butylphenol
5aa, (55)
5ad, (67)
5ba, 60 (58)
5bd, 61 (55)
5ca, 61 (42)
5cd, (77)
5da, 44
4-MeC6H4
4-MeC6H4
4-MeOC6H4
4-MeOC6H4
1-Naphthyl
1-Naphthyl
a Determined by 1H NMR.
b Diisopropyl-substituted homoallyl alcohol 1a0 was used instead of 1a.
5dd, 54
OH
a For the reaction with 2a, 4.0 equiv of 2a was used while for 2d,
12.0 equiv of 2d was used.
b Determined by 1H NMR. Isolated yields are in parentheses.
c Diphenyl-substituted homoallyl alcohol 4a0 was used.
iPr
iPr
1a'
c With 5 mol % of [RhCl(cod)]2, 20 mol % of P(cC5H9)3, 30 mol % of
cesium carbonate, and 20 mol % of 2-tert-butylphenol.
OH
Ph
Ph
Table 2. Rhodium-catalyzed allyl transfer from homoallyl alcohols 1
to acrylate esters 2
Ph
4a'
OH
R
[RhCl(cod)]2 (5 mol %)
P(cC5H9)3 (20 mol %)
Cs2CO3 (30 mol %)
ring in 4d decreased the yield slightly probably due to
the steric factors (entries 8 and 9).
Ph
1
2
Ph
+
O
R
O
2-tert-butylphenol (20 mol %)
We are tempted to assume the following reaction mech-
anism (Scheme 1). Initial ligand exchange between a
rhodium species 6 and homoallyl alcohol 7 or 2-tert-
butylphenol (8) with the aid of cesium carbonate
provides 9 or 10. Alkoxides 9 and 10 would be in
equilibrium. Retro-allylation of 95 then occurs to
generate r-allylrhodium, the isomerization of which to
p-allylrhodium would be reversible. Subsequent inser-
tion of 26 followed by b-H elimination provides 11 along
with a rhodium hydride species 12. In the case of homo-
allyl alcohol 7 (R2 = H), isomerization of 11 proceeds in
the same pots to produce conjugated 2,4-hexadienoate
3. In contrast, with the use of homoallyl alcohol 7
(R2 = Ar, R3 = H), the corresponding 6-aryl-2,5-
hexadienoate 11 undergoes iterative 1,4-addition to an
excess of 2 to afford triester 5.7 Rhodium hydride 12
generated in situ reacts with 2 to give oxa-p-allylrho-
dium 13. Subsequent protonolysis with 8 regenerates
10 to complete the catalytic cycle. Although the exact
role of 2-tert-butylphenol (8) is not clear yet, it could
work as a mediator converting oxa-p-allylrhodium 13
to 9. Namely, the protonolysis of 13 with 8 would be
much faster than that with 7.8
toluene, reflux, 10 h
X
X
3
Entry
1
R
2
X
3, Yielda (%), E:Z
1
2
3
4
5
6
7
8
9
1a
1a
1a
1b
1b
1c
1c
1d
1d
Me
Me
Me
Ph
2a
2b
2c
2a
2d
2a
2d
2a
2d
OnBu
OtBu
NMe2
OnBu
OMe
OnBu
OMe
OnBu
OMe
3aa, 70 (55), —
3ab, Trace
3ac, (33), —
3ba, 63 (50), 78:22
3bd, (70),b 81:19
3ca, 64 (54), 86:14
3cd, 65 (58), 80:20
3da, 74 (42), 85:15
3dd, 52 (47), 79:21
Ph
4-MeC6H4
4-MeC6H4
3-CF3C6H4
3-CF3C6H4
a Determined by 1H NMR. Isolated yields are in parentheses. The E/Z
ratios were tentatively assigned by comparing the 1H NMR spectra
of (E)- with (Z)-3bd.
b 1,4-Adduct, methyl 5-phenyl-5-hexenoate was obtained in 2% yield.
Next, we tested allyl transfer reactions of homoallyl
alcohols 4 having an aryl group at the allylic position
to acrylate esters 2a and 2d (Table 3). Homoallyl alcohol
4a0 was subjected to the standard conditions to furnish
the unexpected triester 5aa4 in 35% (entry 1). In this
case, dimethyl-substituted homoallyl alcohol 4a gave
better results (entries 2 and 3). The transfers of 4-meth-
ylphenyl- and 4-methoxyphenyl-substituted allyl moie-
ties were also performed (entries 4–7). A naphthalene
In summary, we have extended the scope of the rho-
dium-catalyzed allyl transfer reaction. The allylrhodium
was found to undergo addition to activated olefin.9

M. Jang et al. / Tetrahedron Letters 48 (2007) 4003–4005
4005
OH R3
2210–2211; (e) Hayashi, S.; Hirano, K.; Yorimitsu, H.;
Oshima, K. J. Organomet. Chem. 2007, 692, 505–513.
2. Retro-allylations from lithium, magnesium, and zinc alk-
oxides were observed. (a) Benkeser, R. A.; Siklosi, M. P.;
Mozdzen, E. C. J. Am. Chem. Soc. 1978, 100, 2134–2139;
(b) Gerard, F.; Miginiac, P. Bull. Chim. Soc. Fr. 1974,
2527–2533; (c) Jones, P.; Knochel, P. J. Org. Chem. 1999,
64, 186–195; Under harsh conditions, retro-allylation took
place by the action of tin: (d) Peruzzo, V.; Tagliavini, G. J.
Organomet. Chem. 1978, 162, 37–44; (e) Giesen, V. Disser-
tation University Marburg, 1989; Dibutyltin oxide-cata-
lyzed allyl transfer: (f) Yanagisawa, A.; Aoki, T.; Arai, T.
Synlett 2006, 2071–2074; Ruthenium-catalyzed deallylation
was reported: (g) Kondo, T.; Kodoi, K.; Nishinaga, E.;
Okada, T.; Morisaki, Y.; Watanabe, Y.; Mitsudo, T. J. Am.
Chem. Soc. 1998, 120, 5587–5588.
LnRh
O
LnRh
R3
2
R1
R2
R1 R1
R2
R2
R1
R2
7
R3
R3
OH
tBu
R3
O
LnRh
O
X
8
R2
LnRh
X
R1 R1
9
7 or 8
R3
O
8
7
8
7
Cs2CO3
R2
LnRh Cl
– HCl
6
LnRh
11
O
2
8
tBu
O
LnRh
LnRh
12
H
H
X
10
13
O
H
X
3. Takada, Y.; Hayashi, S.; Hirano, K.; Yorimitsu, H.;
Oshima, K. Org. Lett. 2006, 8, 2515–2517.
4. See Supplementary data for the structural assignment of 5.
5. Retro-allylation of homoallyloxyrhodium complexes to
generate p-allylrhodium species was reported. (a) Zhao,
P.; Incarvito, C. D.; Hartwig, J. F. J. Am. Chem. Soc. 2006,
128, 9642–9643; Instead of the retro-allylation via six-
membered transition state, b-allyl elimination via a four-
membered transition state might operate. Rh-catalyzed b-
alkynyl elimination with tertiary propargyl alcohols was
reported: (b) Funayama, A.; Satoh, T.; Miura, M. J. Am.
Chem. Soc. 2005, 127, 15354–15355; In Rh-catalyzed
reactions of cyclobutanones with arylboronic acids, ring
opening of cyclobutanols via b-carbon elimination took
place. (c) Matsuda, T.; Makino, M.; Murakami, M. Org.
Lett. 2004, 6, 1257–1259; Direct observation of b-aryl
elimination from iminyl- and alkoxyrhodium complexes:
(d) Zhao, P.; Hartwig, J. F. J. Am. Chem. Soc. 2005, 127,
11618–11619; (e) Zhao, P.; Christopher, D. I.; Hartwig, J.
F. J. Am. Chem. Soc. 2006, 128, 3124–3125.
6. Catalytic processes involving intermolecular insertion of
olefins to allylmetals are quite rare. (a) Mitsudo, T.; Zhang,
S.-W.; Kondo, T.; Watanabe, Y. Tetrahedron Lett. 1992,
33, 341–344; (b) Nakamura, H.; Shim, J.-G.; Yamamoto,
Y. J. Am. Chem. Soc. 1997, 119, 8113–8114; (c) Tsukada,
N.; Sato, T.; Inoue, Y. Chem. Commun. 2001, 237–238; (d)
Tsukada, N.; Sato, T.; Inoue, Y. Chem. Commun. 2003,
2404–2405.
7. The isomerization and iterative 1,4-addition would be
caused by the action of cesium carbonate. The use of
potassium carbonate instead of cesium carbonate gave
mixtures of 11 and 3 and of 11 and 5, respectively.
8. The proton exchange of oxa-p-allylrhodium with phenols:
Moss, R. J.; Wadsworth, K. J.; Chapman, C. J.; Frost, C.
G. Chem. Commun. 2004, 1984–1985.
9. Allylation of aldehydes and ketones with allylrhodium was
reported. (a) Shi, M.; Lei, G.-X.; Masaki, Y. Tetrahedron:
Asymmetry 1999, 10, 2071–2074; (b) Masuyama, Y.;
Kaneko, Y.; Kurusu, Y. Tetrahedron Lett. 2004, 45,
8969–8971. Also see: Ref. 3.
R3
O
R2 = Ar, R3 = H
R2 = H
Isomerization
R2
5
3
X
Iterative
1,4-addition
11
Scheme 1.
Further development of the retro-allylation system in
other transformations catalyzed by transition metals is
currently underway.
Acknowledgments
This work was supported by Grants-in-Aid for Scientific
Research and COE Research from the Ministry of
Education, Culture, Sports, Science, and Technology,
Japan. K.H. acknowledges JSPS for financial support.
Supplementary data
Supplementary data (experimental details and charac-
terization data for new compounds) associated with this
article can be found, in the online version, at
doi:10.1016/j.tetlet.2007.04.039.
References and notes
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