Ruthenium catalyzed addition reaction of carboxylic acid across olefins without β-hydride elimination

Article abstract of DOI:10.1039/b404229h

The cationic ruthenium catalyst (Cp*RuCl₂) ₂/AgOTf/Ligand promotes the addition reaction of carboxylic acids across olefins without β-hydride elimination.

Full text of DOI:10.1039/b404229h

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Ruthenium catalyzed addition reaction of carboxylic acid across olefins
without b-hydride elimination
Yohei Oe,* Tetsuo Ohta and Yoshihiko Ito
Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Kyotanabe,
Kyoto, 610-0394, Japan. E-mail: tota@mail.doshisha.ac.jp
Received (in Cambridge, UK) 19th March 2004, Accepted 18th May 2004
First published as an Advance Article on the web 15th June 2004
The cationic ruthenium catalyst (Cp*RuCl
promotes the addition reaction of carboxylic acids across olefins
without b-hydride elimination.
2
)
2
/AgOTf/Ligand
2 2 3
(Cp*RuCl ) /6AgOTf/2Ph P as a catalyst gave exo-2-norbornyl(2-
methoxy)benzoate (5b) in 71% yield (entry 5). Effects of phosphine
ligands on the ruthenium complexes are examined, indicating that
sterically bulky phosphines increase the product yield. So far,
Synthetic organic reactions promoted by transition metal complex
catalysts have attracted much attention because of their high yields
and selectivities. Recently, more efficient organic reactions of the
so-called atom economy have been desired from environmental
a
Table 1 Addition reaction of o-anisic acid (3b) across 2-norbornene (4a)
1
view-point. In general, addition reaction may provide the most
“
atom-economic” reaction. Moreover, unless the catalytic reactions
promoted by transition metal complexes are accompanied by the
formation of intractable materials such as inorganic salts, the metal-
catalyzed reactions will be useful for synthetic organic transforma-
tions, which are suitable for “Green Chemistry”.
Entry
Catalyst
None
Ligand
Yield (%)b
No reaction
29
0
Trace
71
82
83
91
In the previous paper, we have reported the novel intramolecular
cyclization reaction of 2-allylphenol to 2,3-dihydro-2-methylben-
1
2
3
4
5
6
7
8
None
None
c
d
TfOH
2
zofuran catalyzed by ruthenium complex as below. Of note is that
(Cp*RuCl
(Cp*RuCl
(Cp*RuCl
(Cp*RuCl ) /6AgOTf
(Cp*RuCl
(Cp*RuCl
2
2
2
)
)
)
2
2
2
Ph
3
Ph
3
Ph
3
P
P
P
the intramolecular cyclization ends up without involvement of b-
hydride elimination. It is contrasted with some transition-metal
catalyzed nucleophilic additions to olefins which proceed with b-
hydride elimination, as exemplified by the Wacker reaction.3
Consequently, the transition metal catalysts, which are reduced
through the cyclization process, have to be reoxidized to maintain
catalytic activity. On the other hand, the present ruthenium-
catalyzed cyclization needs no oxidant and gives saturated product
in high yield directly with high atom economy.†
/6AgBF
/6AgOTf
4
2
2
2
2
2
2
(tol) P
3
)
)
/6AgOTf
/6AgOTf
dppe
dppb
a
Reaction condition; o-anisic acid (1.0 mmol), 2-norbornene (1.0 mmol),
catalyst (0.01 mmol), ligand (0.02 mmol), PhMe (2.0 mL), at 85 °C, for 18
b
c
h, under Ar. Isolated yield based on 2-norbornene. 10 mol% of TfOH
was used. d exo/endo = 75/25.
a
Table 2 Addition reaction of carboxylic acids across 2-norbornene in the
2 2
presence of (Cp*RuCl ) /AgOTf/dppb
Now our attention has been focused on the intermolecular
version of nucleophilic addition of carboxylic acid to olefins,
producing carboxylic acid esters. The Ru-catalyzed addition
reaction of carboxylic acids to alkynes to give the corresponding
4
5
Carboxylic acid
Product
Yield (%)
b
vinyl esters were reported by Mitsudo et al., Dixneuf et al. and
6
Koley et al. Recently, Hartwig and co-workers have reported the
hydroamination reaction of styrene derivatives catalyzed by Pd and
Ru catalysts.7 However, the transition-metal-catalyzed addition
reaction of the oxygen nucleophiles across olefins, which may
involve a common mechanistic feature to the hydroamination
reaction, has not been reported. If the title addition reaction
proceeds smoothly under mild conditions, it may provide a new
entry to regio- and stereo-selective olefin hydration, i.e., the
saturated esters produced through the addition reaction undergo
selective hydrolysis to give the alcohols together with the
corresponding carboxylic acids, which are identical to the starting
carboxylic acids, which are reusable as starting materials.
6
9
7
3
1
0
The results of the addition reaction of o-anisic acid (3b) across
90
0
2-norbornene (4a) under various conditions are summarized in
Table 1. In the absence of ruthenium complex catalyst, no addition
reaction took place (entry 1). Treatment of 3b with 4a in the
presence of 10 mol% of trifluoromethanesulfonic acid (TfOH)
under the same conditions gave exo- and endo-2-norbornyl
a
Reaction condition; carboxylic acid (1.0 mmol), 2-norbornene (1.0 mmol),
Cp*RuCl /4AgOTf/2dppb (0.01 mmol), PhMe (2.0 mL), at 85 °C, for 18
h, under Ar. Isolated yield based on 2-norbornene.
2
(
-methoxybenzoates in 29% yield with a ratio of exo/endo = 75/25
entry 2). (Cp*RuCl /2PPh and (Cp*RuCl /6AgBF /2Ph
had no catalytic activities (entry 3, 4). However, use of 1.0 mol% of
(
2 2
)
2
)
2
3
2
)
2
4
3
P
b
1
620
C h e m . C o m m u n . , 2 0 0 4 , 1 6 2 0 – 1 6 2 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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a
Table 3 Addition reaction of o-anisic acids across olefins
developed. This reaction gave the corresponding esters in good to
excellent yields. Moreover, 2-allylanisole gave the corresponding
ester in 50% yield. This finding presents a first example of
intermolecular addition reaction of carboxylic acid across olefins
without b-hydride elimination. The addition reaction coupled with
hydrolysis under mild conditions may be useful as an olefin
8
hydration procedure. Further studies on the scope and limitations
of the addition reaction as well as the reaction mechanism are now
in progress.
Entry
1
Olefin
Product
Yield (%)b
0
This work was partially supported by Doshisha University’s
Research Promotion Fund, and a grant to RCAST at Doshisha
University from the Ministry of Education, Japan. This work was
supported by Grant-in-Aid for Scientific Research on Priority
Areas (No.16033259, “Reaction Control of Dynamic Complexes”)
from Ministry of Education, Culture, Sports, Science and Technol-
ogy, Japan.
2
4
3c
50
a
Reaction condition; o-anisic acid (1.0 mmol), olefin (1.0 mmol),
Notes and references
† Typical procedure of addition reaction of carboxylic acids across olefins:
(
2 2
Cp*RuCl ) /4AgOTf/2dppb (0.01 mmol), PhMe (2.0 mL), at 85 °C, for 18
h, under Ar. Isolated yield based on olefin. c PPh
b
was used instead of
3
dppb.
2 2
(Cp*RuCl ) (6.2 mg, 0.01 mmol) was dissolved in toluene (2 mL) and the
solution was heated to 85 °C. After 15 min, AgOTf (15.5 mg, 0.06 mmol)
was added and stirred at 85 °C for 3 h. Dppb (8.6 mg, 0.02 mmol) was added
and stirred for 1 h. The reaction mixture was cooled to room temperature. o-
Anisic acid 3b (152 mg, 1.0 mmol) and 2-norbornene 4a (94 mg, 1.0 mmol)
were added. The reaction mixture was heated to 85 °C and stirred for 18 h.
The crude product was dissolved in diethyl ether (50 mL) and organic layer
was washed with water (30 mL, twice), brine (20 mL) and dried over
sodium sulfate. The product was purified by silica gel chromatography
1
,4-diphenylphosphinobutane(dppb) is a ligand of choice in the
catalytic reaction (entry 8).
Under the condition described in Table 1 (entry 8), reactions of
various carboxylic acids (3a–3e) with 4a were also attempted
(Table 2). Benzoic acids with electron-donating group (3a–b, 3d)
gave better yields. However, addition reaction of 2,6-dimethox-
ybenzoic acid (3a) with 4a afforded the corresponding adduct, but
in diminished yield (63%), probably due to steric congestion. On
the other hand, no reaction took place when acetic acid (3e) was
used as a starting material, although no reasonable mechanistic
explanation was so far given.
However, of note is that only the exo-isomer was selectively
formed. The stereoselective formation of an exo-adduct may
suggest that exo-ruthenium coordination is crucially important
prior to the product formation.
(hexane/ethyl acetate = 4/1), yielding product 5b (224 mg, 91%).
1 For reviews see B. M. Trost, Acc. Chem. Res., 2002, 35, 695–705.
2 K. Hori, H. Kitagawa, A. Miyoshi, T. Ohta and I. Furukawa, Chem Lett,
1
998, 1083–1084 and unpublished data.
(a) J. Tsuji, Palladium Reagents and Catalyst, John Wiley & Sons, 1995;
b) P. M. Henry, Palladium Oxidation of Hydrocarbons, D. Reidel Pub.
3
(
Co., 1980; (c) R. F. Heck, Palladium Reagent in Organic Synthesis,
Academic Press, 1985.
4
(a) T. Mitsudo, Y. Hori, Y. Yamakawa and Y. Watanabe, J. Org. Chem.,
1
985, 50, 1566–1568; (b) T. Mitsudo, Y. Hori, Y. Yamakawa and Y.
More examples of the addition reaction of carboxylic acids to
olefins were shown (Table 3). When allylbenzene (4b) was used, no
reaction was observed (entries 1). This failure may suggest that
stronger p-coordination of 2-norbornene onto ruthenium metal
center than the simple terminal olefins might favorably induce the
addition reaction. Successful addition of 2-allyl anisole (4c) may be
due to a possible chelating coordination of the olefin substrate
Watanabe, J. Org. Chem., 1987, 52, 2230–2239.
5 J. Le Paih, S. Dérien and P. H. Dixneuf, Chem. Commun., 1999,
1437–1438.
6
L. J. Goosen, J. Paetzold and D. Koley, Chem. Commun., 2003,
06–707.
(a) M. Utsunomiya and J. F. Hartwig, J. Am. Chem. Soc., 2003, 125(47),
4286–14287; (b) M. Utsunomiya, R. Kuwano, M. Kawatsura and J. F.
7
7
1
Hartwig, J. Am. Chem. Soc., 2003, 125(19), 5608–5609; (c) M.
Utsunomiya and J. F. Hartwig, J. Am. Chem. Soc., 2004, 126(47),
(entry 2). Triphenylphosphine ligand can enhance this chelating
effect, increasing the yield of 5g (entry 3).
In conclusion, novel catalytic addition of benzoic acids with
2
702–2703.
8 Hydrolysis reaction toward the recyclable olefin hydration is in
development.
2-norbornene without accompanying b-hydride elimination was
C h e m . C o m m u n . , 2 0 0 4 , 1 6 2 0 – 1 6 2 1
1621