[IrCl(cod)]2-catalyzed direct oxidative esterification of aldehydes with alcohols

Article abstract of DOI:10.1016/j.tet.2007.10.003

[IrCl(cod)]₂ catalyzed the oxidative esterification of a variety of aldehydes with methanol as a solvent in combination with K₂CO₃ under mild conditions (rt, 12 h). The oxidative esterification reaction of aliphatic aldehydes also took place with olefinic alcohols as reagents in toluene under similar conditions.

Full text of DOI:10.1016/j.tet.2007.10.003

Tetrahedron 63 (2007) 12695–12701
[IrCl(cod)]2-catalyzed direct oxidative esterification of
aldehydes with alcohols
a
a
b
b
Syun-ichi Kiyooka,a, Yosuke Wada, Mahuyu Ueno, Takeshi Yokoyama and Reiko Yokoyama
*
aDepartment of Materials Science, Faculty of Science, Kochi University, Akebono-cho, Kochi 780-8520, Japan
bDepartment of Anesthesiology and Critical Care Medicine, Kochi Medical School, Oko-cho, Nankoku 783-8505, Japan
Received 6 September 2007; revised 1 October 2007; accepted 1 October 2007
Available online 5 October 2007
Abstract—[IrCl(cod)]2 catalyzed the oxidative esterification of a variety of aldehydes with methanol as a solvent in combination with K2CO3
under mild conditions (rt, 12 h). The oxidative esterification reaction of aliphatic aldehydes also took place with olefinic alcohols as reagents
in toluene under similar conditions.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
From a viewpoint of green chemistry, transition metal-cata-
lyzed oxidative esterification is expected to be a versatile
procedure directly giving esters from aldehydes and alco-
hols. Such oxidative esterification reactions, however, have
not been reported frequently until now.1 The actual reaction
providing esters has been considered to proceed through the
oxidative addition of low-valency transition metal species to
the oxygen–hydrogen bond of alcohol to give an alkoxide
and the attack of the resulting alkoxy group on the aldehyde
carbonyl coordinated to the metal followed by the b-hydride
elimination from the metal-bound hemiacetal intermediate.
The b-hydride elimination is the most important step in
the sequential processes of the oxidative esterification. Re-
cently, Cp* iridium complexes are attracting much attention
for their effectiveness for the b-hydride elimination as an ox-
idation process of alkoxo complexes.2 In order to clarify the
oxidative esterification using iridium complexes, we applied
[IrCl(cod)]2 to the oxidative esterification of aldehydes
with alcohols because the iridium complex is commercially
available and known to be useful for a variety of catalytic re-
actions in organic synthesis.3 We disclose herein an oxida-
tive esterification of a variety of aldehydes with simple
alcohols as solvents in the presence of a catalytic amount
of [IrCl(cod)]2 in combination with K2CO3 at rt. Further-
more, when alcohols having an olefinic moiety were used
as a reagent in toluene, the oxidative esterification reaction
of aliphatic aldehydes took place under similar conditions.
2.1. Iridium-catalyzed oxidative esterification of
aldehydes with solvent alcohols
When benzaldehyde was stirred overnight in methanol in the
presence of [IrCl(cod)]2, the acetal, PhCH(OCH3)2, was
only obtained in a considerable yield. The iridium complex
apparently works as a Lewis acid in the case. However, the
addition of K2CO3 under the same conditions dramatically
altered the reaction course. It converted [IrCl(cod)]2 to its al-
koxo complex at rt.2–4 Thus, the reaction of benzaldehyde
with a large excess of methanol in the presence of [IrCl-
(cod)]2 in combination with K2CO3 resulted in an oxidative
esterification to give the corresponding ester. When benzal-
dehyde (1 mmol) was stirred overnight in methanol (1 mL)
with [IrCl(cod)]2 (0.02 mmol) and K2CO3 (0.1 mmol),
a mixture of the ester and benzyl alcohol was obtained in
47% yield (Eq. 1, entry 1 in Table 1); the yield is calculated
on the basis of the starting aldehyde. The ratio of the ester to
benzyl alcohol was almost 1:1. The result allows us to con-
sider the two different reactions, i.e., the esterification and
the reduction, which coincidentally took place in a catalytic
cycle. The reaction of benzaldehyde with simple alcohols as
solvents was investigated, as shown in Table 1. The optimal
quantity of methanol was adequate to be 2 mL (entry 2).
When the quantity of methanol was used in large excess,
the ratio of benzyl alcohol to ester was increased owing to
the enhanced reduction of benzaldehyde (entry 3). A lower
loading of the catalyst (1 mol %) resulted in a moderate yield
(entry 4). Although a considerable amount of ethyl acrylate
was added to the reaction mixture as hydrogen acceptor1e in
order to reduce the reduction to benzyl alcohol, the result
was not improved. At an elevated temperature the reduction
Keywords: [IrCl(cod)]2; Oxidative esterification without oxidants; Direct
esterification of aldehydes.
* Corresponding author. Tel.: +81 88 844 8295; fax: +81 88 844 8359;
e-mail: kiyooka@cc.kochi-u.ac.jp
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.10.003

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S.-ichi Kiyooka et al. / Tetrahedron 63 (2007) 12695–12701
Table 1. Iridium-catalyzed oxidative esterification of benzaldehyde (1 mmol) with a large excess of simple alcohols under mild conditions at rt for 12 h in the
presence of [IrCl(cod)]2 and K2CO3 (Eq. 1)
Entry
[IrCl(cod)]2 (mmol)
Solvent ROH (mL)
Yielda (%)
Ratios of ester and benzyl alcoholb
1
2
3
4
5c
6
7
0.02
0.02
0.02
0.01
0.02
0.02
0.02
CH3OH (1)
CH3OH (2)
CH3OH (5)
CH3OH (2)
CH3OH (2)
C2H5OH (2)
(CH3)2CHOH (2)
47 (1)
87 (1)
85 (1)
78 (1)
82 (1)
57 (2)
13 (3)
1:1.1
1:1.1
1:1.5
1:1.2
1:1.8
1:3.2
1:2.6
a
The isolated yields are shown as a sum of the ester and benzyl alcohol.
The ratios were obtained from their 1H NMR spectra.
The reaction was carried out under reflux conditions.
b
c
preferentially took place presumably owing to the hydride
source supplied increasingly by the b-hydride elimination
from the coordinated solvent methanol (entry 5). When ethanol
was used, the reaction proceeded increasing the ratio of the
reduction to benzyl alcohol (entry 6). It is noteworthy that
ethanol is more rapidly oxidized by the iridium complex,
compared with methanol in supplying more hydride species.
On the other hand, the reaction with isopropanol resulted in a
low yield, presumably depending on the lower nucleophilicity
owing to the steric property as a secondary alcohol (entry 7).
methoxy group leads to the hemiacetal species c. The b-
hydride elimination at the species c produces the ester
and the resulting hydride species d. The iridium hydride
(d) can reduce benzaldehyde to give benzyl alcohol (via
e). The intermediate a is recovered by solvolysis of the
species f with excess methanol in delivering benzyl alco-
hol. Excess reduction of benzaldehyde might proceed by
another iridium hydride species, probably supplied by an
alternative hydride transfer from the coordinated alkoxo
intermediate g.
[IrCl(cod)]2 (0.02 mmol) / K2CO3 (0.1 mmol)
rt, 12 h
PhCHO
(1 mmol)
ROH
PhCOOR
ester
PhCH2OH
benzyl alcohol
simple alcohol as solvent
ð1Þ
1 R = CH3
2 R = C2H5
3 R = (CH3)2CH
The iridium-catalyzed oxidative esterification reaction can
be explained, as shown in Scheme 1. A large excess of
methanol feasibly converts [IrCl(cod)]2 to its iridium me-
thoxo intermediate a by the assistance of K2CO3. Benzal-
dehyde coordinates to the intermediate to give the species
b as the carbonyl function being activated by the metal.
The following intramolecular nucleophilic migration of
Although the hydride transfer (redox) processes involving
the intermediates c, e, and g are supposed to be in equilib-
rium, the large excess of solvent methanol provides a driving
force for the catalytic cycle.
The result of the iridium-catalyzed oxidative esterification
of a variety of aldehydes with methanol is summarized in
[IrCl(cod)]2 + K2CO3 + excess CH3OH
- (KHCO3 + KCl)
PhCH2OH
CH3OH
PhCHO
Ir
OCH3
a
Ir
f
Ir
O
b
O
OCH3
Ir
Ph
Ph
H
O
O
g
O
H
Ph
H
Ir
Ph
OCH3
H
e
O
Ir
PhCH2OH
c
Ph
H
O
H
OCH3
PhCHO
Ph
Ir
H
d
Scheme 1. A plausible reaction mechanism of the oxidative esterification of benzaldehyde with excess methanol accompanied by the reduction of benzaldehyde.
(Coordinated solvents to the iridium metal are omitted from the scheme for its simplicity.)

S.-ichi Kiyooka et al. / Tetrahedron 63 (2007) 12695–12701
12697
Table 2. Iridium-catalyzed oxidative esterification of a variety of aldehydes with methanol (Eq. 2)
Entry
Aldehydes
K2CO3 (mmol)
Reaction time (h)
Yielda (%)
Ratios of ester and alcoholb
1
2
3
4
5
6
7
8
p-Tolualdehyde
p-Tolualdehyde
0.1
0.1
0.1
0.1
0.3
0.1
0.3
0.1
0.1
0.3
0.1
12
24
12
24
24
24
24
24
30
30
24
60 (4+11)
84 (4+11)
78 (5+12)
62 (6+13)
82 (6+13)
20 (7+14)
65 (7+14)
55 (8+15)
54 (9+16)
88 (9+16)
46 (10+17)
1:1
1:1
1:1
1:1
p-Nitrobenzaldehyde
2-Naphthaldehyde
2-Naphthaldehyde
1-Naphthaldehyde
1-Naphthaldehyde
4-Phenylbenzaldehyde
Hydrocinnamaldehyde
Hydrocinnamaldehyde
Cinnamaldehyde
1:1
1:2.1
1:3.6
1:1.1
1:1.3
1:1.5
1:1.2
9
10
11
a
The isolated yields are shown as a sum of the ester and benzyl alcohol.
The ratios were obtained from their 1H NMR spectra.
b
Table 2 (Eq. 2). Long reaction time is occasionally re-
quested for good yields comparable with that of benzalde-
hyde (entry 2). The yields were furthermore improved by
increasing the quantity of K2CO3 (entries 5, 7, and 10).
The reduction to the corresponding alcohol was preferen-
tially observed with respect to 1-naphthaldehyde having
some steric bulkiness owing to retardation of the alkoxide
attack (entries 6 and 7). Similarly, less reactive hydrocin-
namaldehyde as a representative of aliphatic aldehydes re-
sulted in a moderate yield with a slight excess of the
alcohol (entries 9 and 10).
2.2. Iridium-catalyzed oxidative esterification reaction
of aldehydes with olefinic alcohols
The transition metal-catalyzed isomerization of allylic alco-
hols to the corresponding carbonyl compounds is considered
to proceed via a process involving hydrogen 1,3-shift with
a hydrido-p-allylic intermediate (a) and the sequential keto-
nization through a hydrido-p-oxyallylic intermediate (b) as
depicted in Scheme 2.7 Iridium complexes are known to be
effective for the isomerization of allylic alcohols to alde-
hydes and ketones.8,9,10 The isomerization of allylic alcohol
[IrCl(cod)]2 (0.02 mmol) / K2CO3, rt
RCHO
(1 mmol)
CH3OH
(2 mL)
RCOOCH3
methyl ester
4 ~ 10
RCH2OH
alcohol
11 ~ 17
ð2Þ
We tried the oxidative esterification using simple alcohols
as substrates, but the formation of the ester could not be
appreciated in the reaction of benzaldehyde with methanol
as a substrate (2 mol equiv) in THF and toluene. Under
similar conditions, the reactions with 3-phenyl-1-propanol
and 1-methyl-1-propanol also did not proceed at all. Even
2-pyridylmethanol did not work, which seems to be
effective for precoordination to transition metal centers.5
However, it has been reported that alcohols, in which
two alcohol functional groups are converged, undergo
the oxidative esterification mediated by Cp* iridium com-
plexes to give the corresponding lactones.6a,b Alcohols
obtained directly from aldehydes are effective for Tish-
chenko dimerization to give esters in the presence of an
Ir–ligand bifunctional catalyst, which was in situ prepared
from the corresponding Ir complex and 2-propanol. The
Ir-catalyzed Tishchenko reaction seems to proceed in
a manner similar to Scheme 1.6c,d
by [IrCl(cod)]2 was reported to propanal along with byprod-
ucts: propene and diallyl ether.10 When reinvestigated the
iridium-catalyzed isomerization reaction of cinnamyl alco-
hol under mild conditions ([IrCl(cod)]2 (5 mol %), rt, 12 h,
THF) in combination with K2CO3 (10 mol %), we inciden-
tally found the ester formation as a self-condensation in
the iridium-catalyzed isomerization reaction, as shown in
Eq. 3.11 The formation of the esters formally corresponds
to the esterification of hydrocinnamic acid with cinnamyl
and hydrocinnamyl alcohols (20 and 21). The whole process
of the ester formation must be followed by C–O bond forma-
tion and subsequent oxidation during the isomerization of
the allylic alcohol to the corresponding alcohol. Conse-
quently, it resulted in a novel iridium-catalyzed oxidative es-
terification of an aliphatic aldehyde with an olefinic alcohol
in THF. This condensation might be possible essentially by
the precoordination of the olefinic moiety of the alcohol to
the iridium center, as an anchor effect.12
[IrCl(cod)]2 (5 mol%)
K2CO3 (10 mol%)
CHO
Ph
Ph
OH
Ph
Ph
OH
THF, rt, 12 h
(19%)
19
(recovered 10%)
(10%)
18
ð3Þ
O
O
Ph
O
Ph
Ph
O
20 (37%)
21 (12%)

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S.-ichi Kiyooka et al. / Tetrahedron 63 (2007) 12695–12701
Table 3. Iridium-catalyzed oxidative esterification of hydrocinnamaldehyde
with cinnamyl alcohol
OH
OH
OH
M
[IrCl(cod)]2 (5 mol%)
K CO (10 mol%)
M
/
H
a
CHO
2
3
Ph
OH
Ph
solvent, rt, 12 h
OH
O
H
O
O
M
M
b
Ph
O
Ph
Ph
OH
Ph
O
Ph
20
21
a small amount
OH
CHO
Entry
Aldehyde/alcohol
Solvents
Yieldsa of 20 and 21
Scheme 2. Transposition of allylic alcohols into carbonyl compounds medi-
ated by transition metal complexes.
1
2
3
4
1:1
1:2
1:2
1:2
THF
THF
Toluene
CH3CN
46 (3:1)
60 (2:1)
97 (3:2)
No reaction
The early stage results in the formation of the iridium alkoxo
complex (b), as shown in Scheme 3. Then, the resulting
complex is introduced into a similar catalytic cycle, depicted
in Scheme 1. In the catalytic cycle, the subsequent intra-
molecular migration of the resulting alkoxy group to the
aldehyde, which was in advance produced via isomerization,
takes place to afford an iridium acetal intermediate, followed
by oxidative hydrogen transfer (b-hydrogen elimination) to
give hydride iridium complexes delivering the product ester.
The complexes can serve some reductions of the double
bonds of the starting alcohol and the product ester and the
aldehyde carbonyl. It is still uncertain whether the cod ligand
remains unchanged over the process.13
a
The isolated yields were determined, based on the starting aldehyde,
although the amount of the aldehyde might be partially increased by
isomerization of cinnamyl alcohol during the reaction.
the optimal conditions,14 the yield unfortunately decreased
to 25% in spite of the expected improvement of the ratio
of 20 to 21 to be 9:1.
Cross-condensations between allylic alcohols and aldehydes
having different structures may be possible because iridium-
catalyzed allylic isomerization is dispensable for this oxida-
tive esterification. The cross-condensations were carried out
using hydrocinnamaldehyde and 2-methylbutyraldehyde as
typical primary and secondary aliphatic aldehydes, as
shown in Table 4. In practice, a variety of primary and sec-
ondary allylic alcohols underwent the iridium-catalyzed
oxidative esterification reaction to afford the corresponding
esters in good yields despite the structural difference of the
allylic alcohols (entries 1–6). When secondary allylic alco-
hols were used, the obtained products were only unsaturated
esters because of the steric hindrance against the reduction
(entries 4 and 5). Furthermore, an interesting feature of
this reaction was found that an olefinic alcohol (27) having
a double bond far from the hydroxy function exactly works
(entry 7). Presumably the remote double bond works effec-
tively for the precoordination to the iridium center to form
the resulting alkoxo complex and allows the attack of the
pendant alkoxo moiety to the coordinated aldehyde to
make the subsequent C–O bond formation possible. The
condensation reaction with 27 allowed to give a small
amount of the ester (21) from 3-phenyl-1-propanol as a re-
duction product of the starting aldehyde because the main
condensation reaction is relatively slow in comparison
with the corresponding reaction with allylic alcohols. Dou-
ble bond isomerization in the product esters was also
observed but in this case the double bonds could not be
reduced.
[IrCl(cod)]2
+
Ph
OH
Ph
Ir
HO
a
isomerization
K2CO3
- (KHCO3 + KCl)
Ph
O
H
Ph
Ir
O
b
16e
into catalytic cycle
Scheme 3. An effective precoordination of cinnamyl alcohol and the
following formation of alkoxo complex at the early stage in the reaction
of Eq. 3.
The condensation was continuously investigated in order to
realize the general iridium-catalyzed oxidative esterification
starting from a primary allylic alcohol and an aldehyde. The
condensation reaction of hydrocinnamaldehyde with cin-
namyl alcohol proceeded in a better yield of the same ester
pair (20 and 21) along with 3-phenyl-1-propanol as a reduc-
tion product, compared with the reaction starting with only
cinnamyl alcohol (Table 3). The best result was obtained
in toluene with a 1:2 molar ratio of the starting aldehyde
to alcohol (entry 3). Acetonitrile was inadequate for the
reaction, probably owing to its strong coordination ability
as covering the catalytic center (entry 4). Although a large
excess of 2-norbornene was added in order to prevent the
reduction of the olefinic ester to the saturated one under
In addition, aromatic aldehyde showed slightly different
behavior in the reaction. The reaction of benzaldehyde
with crotyl alcohol gave a large amount of benzyl alcohol
(42%) along with a small amount of the expected ester
(9%) and the ester (10%) from the aldehyde via the isomer-
ization of the starting alcohol (Eq. 4). The electron-attractive
character of the aromatic moiety, compared to that of
aliphatic one, might be suitable for the reduction under the
reaction conditions.

S.-ichi Kiyooka et al. / Tetrahedron 63 (2007) 12695–12701
12699
Table 4. Iridium-catalyzed oxidative esterification reaction with a variety of olefinic alcoholsa
[IrCl(cod)]2 (5 mol%)
K2CO3 (10 mol%)
olefinic alcohol
unsaturated ester
saturated ester
RCHO
Toluene, rt, 12 h
RCH2OH (20~10%)
+
Entry
1
Aldehydes
Alcohols
Esters (% yield)b
O
O
OH
CHO
Ph
Ph
Ph
Ph
Ph
Ph
O
Ph
O
22
28 (65)
30 (61)
29 (13)
31(20)
O
O
OH
CHO
CHO
CHO
CHO
2
3
4
5
Ph
O
Ph
O
23
O
O
OH
OH
Ph
O
Ph
O
24
32 (57)
33 (18)
O
34 (82)
Ph
O
25
OH
O
35 (80)
Ph
O
26
O
O
CHO
CHO
Ph
OH
6
O
Ph
O
Ph
18
36 (64)
37 (17)
O
O
O
Ph
O
Ph
OH
30 (19)
Ph
38 (42)
7
Ph
O
O
O
27
Ph
O
Ph
39 (17)
21 (6)
a
The reaction conditions of entry 3 in Table 3 were used.
Isolated yields.
b
[IrCl(cod)]2 (5 mol%)
K2CO3 (10 mol%)
4. Experimental
PhCHO
Ph
OH
Toluene, rt, 12 h
4.1. General
ð4Þ
O
O
OH
Ph
O
O
All solvents were dried by standard methods. All reactions
were carried out under an inert atmosphere. Merck silica-
gel 60 (230–400 mesh) was used for flash column chromato-
graphy. All products obtained in the iridium-catalyzed
oxidative esterification are known esters, which were ascer-
(10%)
(42%)
(9%)
1
tained by NMR analyses: H and 13C NMR spectra were
3. Conclusion
recorded with a Jeol JNM-LA 400 spectrometer with tetra-
methylsilane used as an internal standard.
In summary, a variety of aldehydes are directly transferred in
simple alcohol solvents in the manner of the oxidative ester-
ification being accompanied by the sequential reduction of
the aldehydes under mild conditions with catalytic amounts
of [IrCl(cod)]2 in the presence of K2CO3. On the other hand,
the starting alcohols having an olefinic moiety work well as
substrates in the oxidative esterification reaction of aliphatic
aldehydes to give the corresponding esters in good yields.
As long as the starting alcohols are used as solvents, the
alcohols do not need to furnish an olefinic moiety for the
reaction.
4.2. Typical procedure for the oxidative esterification in
simple alcohols
To a mixture of [IrCl(cod)]2 (14 mg, 0.02 mmol) and K2CO3
(14 mg, 0.1 mmol) was added methanol (2 mL) under Ar.
After stirring for 10 min at rt, the solution turned pale yel-
low. Aldehyde (1 mmol) was added dropwise to the solu-
tion. The color of the solution gradually changed dark.
The reaction mixture was stirred at rt overnight and
quenched with saturated NH4Cl (5 mL). The resulting

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S.-ichi Kiyooka et al. / Tetrahedron 63 (2007) 12695–12701
aqueous solution was evaporated in vacuo to a half vol-
ume. Next, ether (10 mL) was added to the residue and
the organic layer was separated. The aqueous layer was
extracted with ether (10 mLꢀ2). The combined organic
layers were dried over anhydrous MgSO4. After evapora-
tion of the solvent, the crude residue was purified by flash
column chromatography on silica-gel to give the ester and
the alcohol.
the solution. The reaction mixture was stirred at rt for 12 h.
The reaction was quenched with saturated NH4Cl (5 mL).
The organic layer was separated and the aqueous layer was ex-
tracted with ether (10 mL ꢀ3). The combined organic layers
were dried over anhydrous MgSO4. After evaporation of the
solvent, the crude residue was purified by flash column chro-
matography on silica-gel to give the resulting esters.
4.3.1. (2E)-3-Phenyl-2-propenyl 3-phenylpropionate 20.
1H NMR (400 MHz, CDCl3) d 2.67 (2H, t, J¼7.8), 2.97
(2H, t, J¼7.8 Hz), 4.27 (2H, dd, J¼1.2, 5.4 Hz), 6.20–6.27
(1H, m), 6.11 (1H, d, J¼15.9 Hz), 7.15–7.38 (10H, m);
13C NMR (100 MHz, CDCl3) d 30.8, 35.7, 64.8, 123.0,
126.1, 126.5 (2C), 127.9, 128.1 (2C), 128.3 (2C), 128.4
(2C), 134.0, 136.0, 140.3, 172.4.
4.2.1. Methylbenzoate 1. 1H NMR (400 MHz, CDCl3)
d 3.89 (3H, s), 7.41 (2H, t, J¼7.8 Hz), 7.53 (1H,
t, J¼7.8 Hz), 8.02 (2H, d, J¼7.3 Hz); 13C NMR
(100 MHz, CDCl3) d 52.0, 128.3 (2C), 130.0 (2C), 130.1,
132.9, 167.1.
1
4.2.2. Methyl 4-methylbenzoate 4. H NMR (400 MHz,
1
CDCl3) d 2.40 (3H, s), 3.90 (3H, s), 7.23 (2H, d, J¼7.8 Hz),
7.93 (1H, d, J¼7.8 Hz); 13C NMR (100 MHz, CDCl3)
d 21.6, 51.9, 127.4, 129.1 (2C), 129.6 (2C), 143.5, 167.2.
4.3.2. 3-Phenylpropyl 3-phenylpropionate 21. H NMR
(400 MHz, CDCl3) d 1.88–1.95 (2H, m), 2.62 (2H, t,
J¼7.8 Hz), 2.67 (2H, t, J¼7.6 Hz), 2.97 (2H, t, J¼7.8 Hz),
4.07 (2H, t, J¼6.6 Hz), 7.15–7.38 (10H, m); 13C NMR
(100 MHz, CDCl3) d 30.0, 30.8, 32.0, 35.6, 63.6, 125.8,
126.1, 128.1 (2C), 128.2 (2C), 128.3 (4C), 140.3, 141.0, 172.6.
4.2.3. Methyl 4-nitrobenzoate 5. 1H NMR (400 MHz,
CDCl3) d 3.99 (3H, s), 8.22 (2H, d, J¼9.0 Hz), 8.30 (2H,
d, J¼9.0 Hz); 13C NMR (100 MHz, CDCl3) d 52.8, 123.5
(2C), 130.7 (2C), 135.4, 150.4, 165.1.
4.3.3. Propenyl 3-phenylpropionate 28. 1H NMR
(400 MHz, CDCl3) d 2.66 (2H, t, J¼7.8 Hz), 2.97 (2H, t,
J¼7.8 Hz), 4.58 (2H, dt, J¼1.3, 5.7 Hz), 5.22 (1H, dq,
J¼1.2, 10.3 Hz), 5.28 (1H, dq, J¼1.5, 17.3 Hz), 5.84–5.94
(1H, m), 7.18–7.31 (5H, m); 13C NMR (100 MHz, CDCl3)
d 30.9, 35.9, 65.1, 118.2, 126.2, 128.3 (2C), 128.5 (2C),
132.1, 140.4, 172.5.
4.2.4. Methyl 2-naphthoate 6. 1H NMR (400 MHz, CDCl3)
d 3.99 (3H, s), 7.55 (1H, t, J¼6.8 Hz), 7.60 (1H, t,
J¼6.8 Hz), 7.88 (2H, d, J¼8.6 Hz), 7.95 (1H, d,
J¼7.8 Hz), 8.06 (1H, d, J¼8.6 Hz), 8.62 (1H, s); 13C
NMR (100 MHz, CDCl3) d 52.3, 125.2, 126.6, 127.4,
127.8, 128.1, 128.2, 129.4, 131.1, 132.5, 135.5, 167.3.
4.3.4. Propyl 3-phenylpropionate 29. 1H NMR (400 MHz,
CDCl3) d 0.91 (3H, t, J¼7.4 Hz), 1.59–1.64 (2H, m), 2.66
(2H, t, J¼7.8 Hz), 2.98 (2H, t, J¼7.8 Hz), 4.03 (2H, t,
J¼6.7 Hz), 7.18–7.31 (5H, m); 13C NMR (100 MHz,
CDCl3) d 10.3, 21.9, 31.0, 35.9, 66.1, 126.2, 128.3 (2C),
128.5 (2C), 140.5, 173.0.
4.2.5. Methyl 1-naphthoate 7. 1H NMR (400 MHz, CDCl3)
d 4.01 (3H, s), 7.52 (2H, quintet, J¼7.8 Hz), 7.63 (1H, t,
J¼7.1 Hz), 7.88 (1H, d, J¼8.3 Hz), 8.02 (1H, d, J¼
8.3 Hz), 8.18 (1H, d, J¼7.3 Hz), 8.91 (1H, d, J¼8.6 Hz);
13C NMR (100 MHz, CDCl3) d 52.2, 124.5, 125.8, 126.2,
127.0, 127.8, 128.5, 130.2, 131.0, 133.4 (2C), 168.0.
1
4.3.5. (2E)-2-Butenyl 3-phenylpropionate 30. H NMR
1
4.2.6. Methyl 4-phenylbenzoate 8. H NMR (400 MHz,
(400 MHz, CDCl3) d 1.71 (3H, dd, J¼1.2, 6.4 Hz), 2.63
(2H, t, J¼7.8 Hz), 2.95 (2H, d, J¼7.9 Hz), 4.50 (2H, dt,
J¼0.96, 6.6 Hz), 5.51–5.60 (1H, m), 5.69–5.81 (1H, m),
7.18–7.30 (5H, m); 13C NMR (100 MHz, CDCl3) d 17.7,
30.9, 35.9, 65.1, 125.0, 126.2, 128.2 (2C), 128.5 (2C),
131.4, 140.5, 172.7.
CDCl3) d 3.94 (3H, s), 7.39 (1H, t, J¼7.1 Hz), 7.47 (2H, t,
J¼7.1 Hz), 7.64 (4H, m), 8.10 (2H, d, J¼8.0 Hz); 13C
NMR (100 MHz, CDCl3) d 52.1, 127.0 (2C), 127.2 (2C),
128.1, 128.8, 128.9 (2C), 130.1 (2C), 139.9, 145.5, 167.0.
4.2.7. Methyl hydrocinnamate 9. 1H NMR (400 MHz,
CDCl3) d 2.63 (2H, t, J¼7.8 Hz), 2.95 (2H, t, J¼8.0 Hz),
3.67 (3H, s), 7.19–7.31 (5H, m); 13C NMR (100 MHz,
CDCl3) d 30.9, 35.7, 51.6, 126.2, 128.2 (2C), 128.5 (2C),
140.5, 173.3.
1
4.3.6. Butyl 3-phenylpropionate 31. H NMR (400 MHz,
CDCl3) d 0.91 (3H, t, J¼7.4 Hz), 1.29–1.39 (2H, m),
1.54–1.61 (2H, m), 2.63 (2H, t, J¼7.8 Hz), 2.95 (2H, t,
J¼7.9 Hz), 4.07 (2H, t, J¼6.7 Hz), 7.18–7.30 (5H, m); 13C
NMR (100 MHz, CDCl3) d 13.5, 18.9, 30.5, 30.8, 35.7,
64.1, 126.0, 128.2 (3C), 128.3, 140.4, 172.7.
1
4.2.8. Methyl cinnamate 10. H NMR (400 MHz, CDCl3)
d 3.78 (3H, s), 6.44 (1H, d, J¼16.0 Hz), 7.27 (3H, m),
7.39 (2H, m), 7.70 (1H, d, J¼16.0 Hz); 13C NMR
(100 MHz, CDCl3) d 51.7, 117.7, 128.0 (2C), 128.7 (2C),
130.3, 134.3, 144.8, 167.4.
4.3.7. 2-Methyl-2-propenyl 3-phenylpropionate 32. 1H
NMR (400 MHz, CDCl3) d 1.75 (3H, s), 2.70 (2H, t,
J¼7.7 Hz), 3.00 (2H, t, J¼7.8 Hz), 4.53 (2H, s), 4.94 (1H,
s), 4.96 (1H, s), 7.19–7.36 (5H, m); 13C NMR (100 MHz,
CDCl3) d 19.4, 30.9, 35.8, 67.6, 126.1, 112.8, 128.2 (2C),
128.4 (2C), 139.8, 140.5, 172.4.
4.3. Typical procedure for the oxidative esterification
with olefinic alcohols
1
Toluene (2 mL) was added to a mixture of [IrCl(cod)]2 (34 mg,
0.05 mmol) and K2CO3 (14 mg, 0.1 mmol) under Ar. Alde-
hyde (1 mmol) and alcohol (2 mmol) were slowly added to
4.3.8. 2-Methylpropyl 3-phenylpropionate 33. H NMR
(400 MHz, CDCl3) d 0.93 (6H, d, J¼6.8 Hz), 1.86–1.98
(1H, m), 2.66 (2H, t, J¼7.6 Hz), 2.99 (2H, t, J¼8.0 Hz),

S.-ichi Kiyooka et al. / Tetrahedron 63 (2007) 12695–12701
12701
3.88 (2H, d, J¼6.8 Hz), 7.19–7.36 (5H, m); 13C NMR
References and notes
(100 MHz, CDCl3) d 19.0 (2C), 27.6, 30.9, 35.8, 70.5,
126.2, 128.2 (2C), 128.4 (2C), 140.4, 172.9.
1. Pd: (a) Lloyd, W. G. J. Org. Chem. 1967, 32, 2816–2819; (b)
Tamaru, Y.; Yamada, Y.; Inoue, K.; Yamamoto, Y.; Yoshida,
Z. J. Org. Chem. 1983, 48, 1286–1292; Ru: (c) Murahashi,
S. I.; Ito, K.; Naota, T.; Maeda, Y. Tetrahedron Lett. 1981,
22, 5327–5330; (d) Murahashi, S. I.; Naota, T.; Ito, K.;
Maeda, Y.; Taki, H. J. Org. Chem. 1987, 52, 4319–4327; Rh:
(e) Grigg, R.; Mitchell, T. R. B.; Sutthivaiyakit, S.
Tetrahedron 1981, 37, 4313–4319; (f) Krug, C.; Hartwig,
J. F. J. Am. Chem. Soc. 2002, 124, 1674–1679; Ni: (g) Han,
R.; Hillhouse, G. L. J. Am. Chem. Soc. 1997, 119, 8135–8136.
2. (a) Bernard, K. A.; Rees, W. M.; Atwood, J. D.
Organometallics 1986, 5, 390–391; (b) Fujita, K.; Furukawa,
S.; Yamaguchi, R. J. Organomet. Chem. 2002, 649, 289–292;
(c) Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organometallics
2004, 23, 1490–1492.
3. (a) Ishii, Y.; Sakaguchi, S. Bull. Chem. Soc. Jpn. 2004, 77, 909–
920; (b) Taguchi, K.; Nakagawa, H.; Hirabayashi, T.;
Sakaguchi, S.; Ishii, Y. J. Am. Chem. Soc. 2004, 126, 72–73;
(c) A variety of Ir complexes are summarized in ‘Recent
advances in iridium-catalyzed organic synthesis’: Takeuchi,
R.; Kezuka, S. J. Synth. Org. Chem. Jpn. 2007, 65, 652–664.
4. (a) The Ir complexes activated by alkyl phosphines are known
to undergo the oxidative addition of aliphatic alcohols without
bases even at low temperature: Blum, O.; Milstein, D. J. Am.
Chem. Soc. 2002, 124, 11456–11467; (b) [IrCl(cod)]2 is known
to be converted to [Ir(cod)(OR)]2 in the presence of Na2CO3 in
alcohol solvents: see Ref. 1f.
4.3.9. 1-Methyl-2-propenyl 3-phenylpropionate 34. 1H
NMR (400 MHz, CDCl3) d 1.28 (3H, d, J¼6.6 Hz), 2.63
(2H, t, J¼7.8 Hz), 2.95 (2H, t, J¼7.8 Hz), 5.11 (1H, dt,
J¼1.2, 10.5 Hz), 5.19 (1H, dt, J¼1.22, 17.4 Hz), 5.32–
5.38 (1H, m), 5.73–5.85 (1H, m), 7.16–7.30 (5H, m); 13C
NMR (100 MHz, CDCl3) d 19.8, 30.9, 36.1, 70.9, 115.7,
126.2, 128.3 (2C), 128.4 (2C), 137.6, 140.5, 172.1.
4.3.10. 1-Octen-3-yl 3-phenylpropionate 35. 1H NMR
(400 MHz, CDCl3) d 0.87 (3H, t, J¼6.8 Hz), 1.25–1.28
(6H, m), 1.48–1.63 (2H, m), 2.63 (2H, t, J¼7.8 Hz), 2.95
(2H, t, J¼7.8 Hz), 5.12 (1H, dt, J¼0.96, 10.5 Hz), 5.17
(1H, dt, J¼1.4, 17.3 Hz), 5.23 (1H, q, J¼6.6 Hz), 5.70–
5.78 (1H, m), 7.16–7.29 (5H, m); 13C NMR (100 MHz,
CDCl3) d 13.9, 22.4, 24.6, 31.0, 31.5, 34.1, 36.1, 74.8,
116.4, 126.2, 128.2 (2C), 128.4 (2C), 136.6, 140.5, 172.1.
4.3.11. (2E)-3-Phenyl-2-propenyl 2-methylbutyrate 36.
1H NMR (400 MHz, CDCl3) d 0.92 (3H, t, J¼7.4 Hz),
1.17 (3H, d, J¼6.8 Hz), 1.43–1.55 (1H, m), 1.65–1.75
(1H, m), 2.34–2.46 (1H, m), 4.74 (2H, dd, J¼1.2, 6.3 Hz),
6.25–6.33 (1H, m), 6.55 (1H, d, J¼15.9 Hz), 7.17–7.14
(5H, m); 13C NMR (100 MHz, CDCl3) d 11.6, 16.6, 26.8,
41.1, 64.7, 123.4, 126.6 (2C), 128.0, 128.6 (2C), 133.9,
136.2, 176.5.
5. The chelation-assisted hydroesterification of alkenes with
2-pyridylmethanol was catalyzed by Rh4(CO)12: Yokota, K.;
Tatamidai, H.; Fukumoto, Y.; Chatani, N. Org. Lett. 2003, 5,
4329–4331.
6. (a) Suzuki, T.; Morita, K.; Tsuchida, M.; Hiroi, K. Org. Lett.
2002, 4, 2361–2363; (b) Suzuki, T.; Morita, K.; Moritsuo, Y.;
Hiroi, K. Tetrahedron Lett. 2003, 44, 2003–2006; (c) Suzuki,
T.; Yamada, T.; Matsuo, T.; Watanabe, K.; Katoh, T. Synlett
2005, 1450–1452; (d) Suzuki, T.; Matsuo, T.; Watanabe, K.;
Katoh, T. Synlett 2005, 1453–1455.
4.3.12. 3-Phenylpropyl 2-methylbutyrate 37. 1H NMR
(400 MHz, CDCl3) d 0.92 (3H, t, J¼7.5 Hz), 1.15 (3H, t,
J¼7.8 Hz), 1.43–1.55 (1H, m), 1.65–1.75 (1H, m), 1.92–
1.99 (2H, m), 2.33–2.46 (1H, m), 2.69 (2H, t, J¼7.7 Hz),
4.09 (2H, dt, J¼1.2, 6.5 Hz), 7.17–7.41 (5H, m); 13C NMR
(100 MHz, CDCl3) d 11.6, 16.6, 26.8, 30.3, 32.1, 41.1,
63.4, 126.0, 128.3 (2C), 128.4 (2C), 141.2, 176.8.
4.3.13. 3-Butenyl 3-phenylpropionate 38. 1H NMR
(400 MHz, CDCl3) d 2.36 (2H, q, J¼6.4 Hz), 2.62 (2H, t,
J¼8.0 Hz), 2.95 (2H, t, J¼8.0 Hz), 4.12 (2H, t, J¼6.4 Hz),
5.05 (1H, dd, J¼1.6, 10.4 Hz), 5.09 (1H, dd, J¼1.6,
16.8 Hz), 5.75 (1H, ddt, J¼6.8, 10.4, 16.8 Hz), 7.15–7.30
(5H, m); 13C NMR (100 MHz, CDCl3) d 31.0, 33.0, 35.9,
63.5, 117.2, 126.2, 128.3 (2C), 128.5 (2C), 134.0, 140.5,
173.0.
ꢀ
ꢀ
7. (a) Uma, R.; Davies, M.; Crevisy, C.; Gree, R. Chem. Rev.
2003, 103, 27–51; (b) Bergens, S. H.; Bosnich, B. J. Am.
Chem. Soc. 1991, 113, 958–967.
8. Davies, S. G. Organotransition Metal Chemistry, Applications
to Organic Synthesis; Pergamon: Oxford, 1982; pp 282–290.
9. (a) Baudry, D.; Ephritikhine, M.; Felkin, H. Nouv. J. Chim.
1977, 2, 355–356; (b) Ohmura, T.; Shirai, Y.; Yamamoto, Y.;
Miyaura, N. Chem. Commun. 1998, 1337–1338.
10. Pannetier, G.; Bonnaire, R.; Fougeroux, P. J. Organomet.
Chem. 1971, 30, 411–419.
11. A preliminary report: Kiyooka, S.-i.; Ueno, M.; Ishii, E.
Tetrahedron Lett. 2005, 46, 4639–4642.
12. The precoordination of olefinic moiety of allylic alcohol to the
ruthenium center was postulated in the ruthenium-catalyzed
reconstitutive condensation of allylic alcohols and terminal
alkynes: Trost, B. N.; Kulawiec, R. J. J. Am. Chem. Soc.
1992, 114, 5579–5584.
1
4.3.14. (2Z)-2-Butenyl 3-phenylpropionate 39. H NMR
(400 MHz, CDCl3) d 1.69 (1H, d, J¼6.8 Hz), 2.59 (2H, t,
J¼7.8 Hz), 2.95 (2H, t, J¼7.8 Hz), 4.64 (2H, d,
J¼7.2 Hz), 5.50–5.60 (1H, m), 5.70–5.80 (1H, m), 7.15–
7.30 (5H, m); 13C NMR (100 MHz, CDCl3) d 13.1, 30.9,
35.9, 60.1, 124.2, 126.2, 128.3 (2C), 128.5 (2C), 129.6,
140.5, 173.0.
Acknowledgements
ꢀ
13. Martın, M.; Sola, E.; Torres, O.; Plou, P.; Oro, L. A.
Organometallics 2003, 22, 5406–5417.
14. Breton, D.; Stefan, J. P.; Dalobor, S. J. Am. Chem. Soc. 2004,
126, 6556–6557.
We thank a Grant-in-Aid for Scientific Research of Japan
Society for the Promotion of Science.