Iridium-catalyzed oxidative methyl esterification of primary alcohols and diols with methanol

Article abstract of DOI:10.1021/jo2003264

Oxidative methyl esterification of primary alcohols and diols with methanol was successfully achieved, using acetone as a hydrogen acceptor, under the influence of an iridium complex combined with 2-(methylamino)ethanol (MAE) as catalyst.

Full text of DOI:10.1021/jo2003264

NOTE
pubs.acs.org/joc
Iridium-Catalyzed Oxidative Methyl Esterification of Primary Alcohols
and Diols with Methanol
Nobuyuki Yamamoto, Yasushi Obora,* and Yasutaka Ishii*
Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita,
Osaka 564-8680, Japan
S Supporting Information
b
ABSTRACT: Oxidative methyl esterification of primary alco-
hols and diols with methanol was successfully achieved, using
acetone as a hydrogen acceptor, under the influence of an
iridium complex combined with 2-(methylamino)ethanol
(MAE) as catalyst.
ethyl esterification is a ubiquitous methodology in organic
the esterification of primary alcohols in methanol by Ru(PPh3)3-
(CO)H2 combined with xantphos in the presence of crotononi-
trile as the hydrogen acceptor.17
In this paper, we disclose a facile, divergent, and atom-
economical methodology for oxidative methyl esterification by
the Ir-catalyzed reaction of primary alcohols and diols with
methanol using acetone as the hydrogen acceptor.
1-Hexanol (1a) with methanol (2) was chosen as the model
substrate, and the reaction was carried out under various condi-
tions (Table 1).
For instance, the reaction of 1a with 2 in the presence of
[Cp*IrCl2]2 (2 mol %) with 2-(methylamino)ethanol (MAE)
(6 mol %) and Cs2CO3 (10 mol %) in acetone at room tempera-
ture for 24 h produced methyl hexanoate (3a) in 84% yield (entry 1).
[Cp*IrCl2]2 showed the best catalytic activity as a catalyst
precursor (entry 1). When [IrCl(cod)]2 and [IrCl(coe)2]2 were
selected as the catalyst precursor, 3a was obtained in lower yields
M
synthesis,1 especially in the transformation of pectins,2
amino acids,3 prostaglandins,4 and peptides.5 Methyl esterifica-
tion has also been successfully applied to the production of
biodiesel fuel (BDF) from waste vegetable oils/fats.6 Various
methods for achieving this reaction have therefore been
developed.7À9 Methyl esters have been prepared by the reaction
of carboxylic acids with methanol under acidic or basic
conditions.7 Another conventional procedure for the synthesis
of methyl esters is reaction of carboxylic acids with trimethylsi-
lyldiazomethane (TMS-CHN2) in methanol solution.8 In addi-
tion, there have been recent reports of the catalytic methyl
esterification of carboxylic acids with methanol.9
Alternatively, oxidative methyl esterification of aldehydes and
alcohols has also attracted considerable interest. However, this
method generally requires stoichiometric amounts of toxic and
hazardous reagents like manganese dioxide or sodium dichro-
mate and/or peroxides.10 The development of a single-step
catalytic direct oxidative methyl esterification of alcohols under
mild conditions is therefore highly desirable from both economic
and environmental points of view. Although several catalytic
oxidative esterifications of primary alcohols to esters have been
reported so far,11 less attention has been paid to the oxidative
methyl esterification of alcohols with methanol.12
It is known that Ir and Ru complexes serve as efficient catalysts
for hydrogen transfer from alcohols to aldehydes,13 and we have
recently developed Ir-catalyzed R-alkylations and β-alkylations
using alcohols as the alkylating agents.14 These results prompted
us to design a reaction system for Ir-catalyzed oxidative dimer-
ization of primary alcohols to esters in the presence of dioxygen
(air) or acetone as a hydrogen acceptor.15 Furthermore, Suzuki
and co-workers have reported that Cp*IrÀaminoalkoxide com-
plexes promote the oxidative dimerization of primary alcohols to
esters in the presence of 2-butanone as the hydrogen acceptor
and K2CO3. However, they did not report the preparation of
methyl esters using cross-esterification of primary alcohols and
methanol.16 Quite recently, Williams and co-workers reported
(entries 2 and 3). IrCl3 3H2O was totally ineffective, and no 3a
3
was formed (entry 4). This reaction was markedly influenced by
the base employed. Among bases examined, Cs2CO3 was found
to be a suitable base (entry 1), but K2CO3 only had moderate
activity, giving 3a in 61% yield (entry 5). Other selected bases
such as Na2CO3, K3PO4, and KOH were less effective, affording
3a in 12%, 61% and 58% yields, respectively (entries 6À8).18 The
addition of a base and MAE was essential for achieving the
reaction, and the reaction in the absence of either a base or MAE
did not produce 3a at all (entries 9 and 10). The yield of 3a was
decreased at elevated temperature because of the instability of the
catalyst (entry 11). In this reaction, acetone functioned as the
best hydrogen acceptor; the reaction using 2-butanone gave a
lower yield of 3a (entry 12). Alkenes like 1-octene were not
efficient hydrogen acceptors (entry 13). The reaction under air
was also found to be sluggish (entry 14).
Received: February 18, 2011
Published: March 18, 2011
r
2011 American Chemical Society
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|

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NOTE
Table 1. Ir-Catalyzed Oxidative Methyl Esterification of 1a
Table 2. Effects of Additives in the Ir-Catalyzed Oxidative
Methyl Esterification of 1a with 2a
with 2a
yieldb (%)
yieldb (%)
conv 1ab (%)
3a
75
4a
entry
Ir complex
base
conv 1ab (%)
3a
4a
entry
additive
1
2
[Cp*IrCl2]2
[IrCl(cod)]2
[IrCl(coe)2]2
IrCl3.3H2O
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
Na2CO3
K3PO4
90
3
84 (80)
1
4
1
2
3
4
5
6
7
EtNH(CH2)2OH
n-PrNH(CH2)2OH
PhNH(CH2)2OH
H2NC2H4OH
81
73
5
2
2
n.d.c
n.d.c
n.d.c
3
66
2
n.d.c
n.d.c
n.d.c
n.d.c
n.d.c
3
2
1
4
<1
73
26
70
71
2
n.d.c
9
3
n.d.c
n.d.c
n.d.c
5
61
Et2N(CH2)2OH
MeNH(CH2)3OH
H2NC2H4NH2
<1
<1
<1
6
12
1
7
61
6
a Conditions: same as for Table 1, entry 1. b GC yields based on 1a used.
8
KOH
58
3
c Not detected by GC.
9
none
n.d.c
n.d.c
56
n.d.c
n.d.c
3
10d
11e
12f
13g
14h
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
11
71
75
<1
<1
65
2
n.d.c
n.d.c
n.d.c
n.d.c
a Conditions: 1a (2 mmol) was allowed to react with 2 (8 mmol) in
the presence of Ir complex (0.04 mmol), MAE (0.12 mmol), and base
(0.1 mmol) in acetone (1 mL) at rt (ca. 25 °C) for 24 h. b GC yields
except the values in the parentheses. c Not detected by GC. d Reaction
was performed in the absence of MAE. e Reaction was performed at
40 °C. f 2-Butanone was used in place of acetone. g 1-Octene was used in
place of acetone. h Reaction was performed in toluene (1 mL) instead of
acetone under air (1 atm).
Figure 1. Effect of the amounts of 1a (2 mmol) and methanol (2)
(2À10 mmol) on yields of 3a and 4a under the conditions for Table 1,
entry 1.
As mentioned above, the addition of MAE was indispensable,
and this effect was investigated using various additives under
the conditions for Table 1, entry 1 (Table 2). Like MAE,
2-(ethylamino)ethanol and 2-(propylamino)ethanol efficiently
promoted the oxidative methyl esterification of 1a with 2 in
75% and 66% yields, respectively (entries 1 and 2). The yield
of 3a decreased with increasing carbon number of the alkyl
group on the amino group. Addition of 2-anilinoethanol and
2-aminoethanol only afforded trace amounts of 3a (entries 3
and 4). Other additives such as diethylaminoethanol, 3-methyl-
aminopropan-1-ol, and ethylendiamine did not afford 3a at all
(entries 5À7).
The scope of the methyl esterification of various primary
alcohols was examined (Table 3). The reaction of 2 with aliphatic
alcohols 1-octanol (1b), 1-decanol (1c), and 1-dodecanol (1d)
afforded the corresponding methyl esters, i.e., methyl octanoate
(3b), methyl decanoate (3c), and methyl dodecanoate (3d), in
83%, 82%, and 92% yields, respectively (entries 1À3). 5-Methyl-
1-hexanol (1e) and 2-ethyl-1-hexanol (1f) afforded the corre-
sponding methyl esters, i.e., methyl 5-methylhexanoate (3e) and
methyl 2-ethylhexanoate (3f), in 82% and 42% yields, respec-
tively (entries 4 and 5). An alcohol (1g) bearing a carbonÀ
carbon double bond provided methyl 7-octenoate (3g), exclu-
sively, without hydrogenation of the double bond (entry 6). An
alcohol (1h) bearing a terminal halogen group was also tolerated
under the reaction conditions and produced methyl 6-chloro-
hexanoate (3h) in good yield (entry 7). Furthermore, various
benzyl alcohols (1iÀl) afforded the corresponding methyl esters,
i.e., methyl benzoate (3i), methyl p-toluate (3j), and methyl
4-chlorobenzoate (3l), in good yields (entries 8À11). Phenethyl
alcohols (1mÀn) also reacted with 2 to produce methyl phenylace-
tate (3m) and methyl (4-chlorophenyl)acetate (3n) in substantial
yields, respectively (entries 12 and 13).
In the reaction, the equimolar reaction of 1a to 2 significantly
affected the yields of 3a and 4a because of the formation of
oxidative dimerization of 1a.15 Figure 1 shows the effect on
the yields of 3a and 4a by changing the amount of methanol (2)
(2 mmolÀ10 mmol) to 1a (2 mmol) under the same conditions
as in entry 1 in Table 1. The reaction of 1a in the absence of
methanol gave 4a in 72% yield, as we previously reported.15
When 2 mmol of 2 were used, i.e., a 1:1 ratio of 1a and 2a, 3a and
4a were obtained in an approximately 3:1 mixture. The use of
excess methanol increased the selectivity of 3a. Thus, the
optimum ratio of 1a to 2 for obtaining 3a in the highest yield,
and with the highest selectivity, was found to be 1:4.
Table 4 shows representative results for the reaction of
methanol 2 with 1,10-decanediol (5a) under the conditions for
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NOTE
Table 3. Oxidative Methyl Esterification of Primary Alcohols
Table 4. Ir-Catalyzed Oxidative Methyl Esterification of r,ω-
(1) with 2a
Diols 5a with 2a
yieldb (%)
entry
base
conv 5ab (%) total yield (%)
6a
7a
1
2
Cs2CO3
K2CO3
Na2CO3
KOH
92
48
69
30
10
82
92
62
38
20
10
44
31
10
n.d.c
3
15
4
90
38
5
6d
K3PO4
K3PO4
>99
64
51 (48) 41 (39)
55
7
a Conditions: 5a (2 mmol) was allowed to react with 2 (8 mmol) in the
presence of [Cp*IrCl2]2 (0.04 mmol), MAE (0.12 mmol), and a base
(0.1 mmol, 10 mol %) in acetone (1 mL) at rt (ca. 25 °C) for 24 h. b GC
yields except the values in the parentheses. c Not detected by GC.
d K3PO4 (0.05 mmol, 5 mol %) was used.
Scheme 1. Methyl Esterification of R,ω-Diols (5bÀd) with 2
a Conditions: same as for Table 1, entry 1. Trace amounts (<2%) of self-
condensation products (4) were detected by GC.
Scheme 2. Ester Exchange of 4a with 2
entry 1, Table 1, using various bases. When the reaction was
performed using Cs2CO3 as the base, the corresponding mono-
methyl ester (6a) and dimethyl ester (7a) were obtained in 38%
and 31% yields, respectively (69% total yield of 6a and 7a; entry 1).
The use of K2CO3 and Na2CO3 led to lower yields (entries 2 and
3). K3PO4 was found to be the best effective base, giving the
highest total yield of 6a and 7a (92%) (entry 5). In addition,
when the amount of K3PO4 was decreased from 10 mol % to 5 mol
% of 5a used, selective monomethyl esterification was promoted to
give 6a as the major product (entry 6).
Scheme 1 shows the results for the reactions of several R,ω-
diols with 2 under the same conditions as for Table 4, entry 5.
The reactions of 1,8-octanediol (5b), 1,9-nonanediol (5c),
and 1,12-dodecanediol (5d) with methanol (2) proceeded
satisfactorily to give mixtures of the corresponding monomethyl
(6bÀd) and dimethyl (7bÀd) esters, in excellent total yields.
To gain insight into the reaction mechanism, some con-
trol experiments were carried out. The reaction might pro-
ceed via ester-exchange between hexyl hexanoate (4a) and
methanol (2), but no ester-exchange product, 3a, was detected
(Scheme 2).
Furthermore, we carried out the ester-exchange reaction of
1-hexanol (1a) and isopropyl alcohol derived from acetone
under these conditions, but no corresponding isopropyl ester
was detected at all.
Next, we performed a competitive experiment using methanol
with alcohol and aldehyde (Scheme 3). If the oxidation of the
alcohols to aldehydes is the rate-determining step, methyl
esterification from aldehyde should be predominant over that
from alcohol. Thus, treatment of an equimolar mixture of 1a and
n-octanal (8) with 2 was carried out under the same conditions as
for entry 1, Table 1. The timeÀyield curves for the formation of
3a and 3b are shown in Figure 2. In the early stage of the reaction
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NOTE
chromatography (230À400 mesh silica gel, n-hexane/ethyl acetate =
10/1) in 80% yield (208 mg).
Typical Reaction Procedure for the Preparation of 6a and
7a (Table 4, Entry 5). To a mixture of [Cp*IrCl2]2 (32 mg, 0.04
mmol), K3PO4 (42 mg, 0.2 mmol), and MAE (9.6 mg, 0.12 mmol) were
added 5a (349 mg, 2 mmol), 2 (256 mg, 8.0 mmol), and acetone
(1.0 mL) under Ar. The reaction mixture was stirred at 25 °C for 24 h.
The conversions and yields of products were estimated by GC, and the
products 6a and 7a were obtained in 92% total yield. The products (6a
and 7a) were isolated by column chromatography (230À400 mesh silica
gel, n-hexane/ethyl acetate = 10/1) in 48 and 39% yield, respectively
(194 and 180 mg).
Figure 2. TimeÀyield curves for the formation of 3a and 3b in the
oxidative methyl esterification of 1a, 8, and 2 under the same conditions
as for Table 1, entry 1.
3a:20a 1H NMR δ 0.82 (t, J = 6.9 Hz, 3H), 1.21À1.26 (m, 4H),
1.52À1.59 (m, 2H), 2.23 (t, J = 7.6 Hz, 2H), 3.6 (s, 3H); 13C NMR δ
174.3 (C), 51.4 (CH3), 34.0 (CH2), 31.3 (CH2), 24.6 (CH2), 22.3
(CH2), 13.9 (CH3).
Scheme 3. Competitive Reaction of Methanol (2) with n-
Hexanol (1a) and n-Octanal (8)
3b:17a 1H NMR δ 0.88 (t, J = 6.6 Hz, 3H), 1.25À1.32 (m, 8H),
1.59À1.65 (m, 2H), 2.30 (t, J = 7.6 Hz, 2H), 3.67 (s, 3H); 13C NMR δ
174.4 (C), 51.5 (CH3), 34.1 (CH2), 31.7 (CH2), 29.2 (CH2), 29.0
(CH2), 25.0 (CH2), 22.6 (CH2), 14.1 (CH3).
3c:20b 1H NMR δ 0.81 (t, J = 6.9 Hz, 3H), 1.19À1.23 (m, 12H),
1.51À1.57 (m, 2H), 2.23 (t, J = 7.6 Hz, 2H), 3.59 (s, 3H); 13C NMR δ
174.3 (C), 51.4 (CH3), 34.1 (CH2), 31.8 (CH2), 29.4 (CH2), 29.2
(CH2), 29.1 (CH2), 24.9 (CH2), 22.6 (CH2), 14.0 (CH3).
3d:20a 1H NMR δ 0.87 (t, J = 6.6 Hz, 3H), 1.25À1.32 (m, 16H),
1.58À1.66 (m, 2H), 2.30 (t, J = 7.6 Hz, 2H), 3.66 (s, 3H); 13C NMR δ
174.4 (C), 51.4 (CH3), 34.1 (CH2), 32.0 (CH2), 29.6 (CH2), 29.5
(CH2), 29.4 (CH2), 29.3 (CH2), 29.2 (CH2), 25.0 (CH2), 22.7 (CH2),
14.1 (CH3).
(ca. 30 min), methyl esterification from aldehyde (8) took place
predominantly, and the resulting methyl esters, 3a and 3b, were
obtained in 18% and 53% yields, respectively (Figure 2). This
result suggests that this reaction involves the oxidation of
alcohols to aldehydes as the key rate-determining step in the
course of the reaction.
It is thought that the reaction proceeds through a hydrogen
transfer pathway similar to that of the reaction reported pre-
viously.13À17 The reaction is initiated by iridium-catalyzed
dehydrogenation of alcohols (1) or R,ω-diols (5) to form the
corresponding aldehydes, which readily undergo acetalization
with methanol (2) to give the hemiacetals. Subsequent dehy-
drogenation of the hemiacetals by the action of the Ir complex
affords the corresponding methyl esters.
Here, an IrÀaminoalkoxylate complex derived from [Cp*IrCl2]2
and MAE seems to be a real active catalyst species as that reported in
the previous literature.15b,16 In addition, we performed the reaction
of hexanal with paraformaldehyde under the same conditions as
for entry 1, Table 1, which resulted no 3a formation. This result
indicates the reaction did not proceed via Tischenko reaction
pathway.19
3e:20c 1H NMR δ 0.88 (d, J = 6.9 Hz, 6H), 1.17À1.30 (m, 2H),
1.52À1.66 (m 2H), 2.04 (s, 1H), 2.29 (t, J = 7.6 Hz, 2H), 3.67 (s, 3H);
13C NMR δ 174.3 (C), 51.4 (CH3), 38.4 (CH2), 34.4 (CH2), 27.8
(CH2), 22.9 (CH2), 22.5 (CH3).
3f:20d 1H NMR δ 0.81 (t, J = 7.3 Hz, 6H), 1.13À1.31 (m, 4H),
1.34À1.60 (m 4H), 2.20 (m, 1H), 3.60 (s, 3H); 13C NMR δ 176.9 (C),
51.2 (CH3), 47.2 (CH), 31.8 (CH2), 29.6 (CH2), 25.5 (CH2), 22.6
(CH2), 13.9 (CH3), 11.8 (CH3).
3g:20e 1H NMR δ 1.23À1.35 (m, 4H), 1.52À1.60 (m, 2H),
1.95À2.01 (m 2H), 2.24 (t, J = 7.6 Hz, 2H), 3.60 (s, 3H) 4.85À4.95
(m, 2H), 5.67À5.77 (m, 1H); 13C NMR δ 174.2 (C), 138.7 (CH), 114.4
(CH2), 51.4 (CH3), 34.0 (CH2), 33.5 (CH2), 28.5 (CH2), 28.4 (CH2),
24.7 (CH2).
3h:20f 1H NMR δ 1.45À1.50 (m, 2H), 1.65À1.68 (m, 2H),
1.80À1.83 (m 2H), 2.33 (t, J = 3.9 Hz, 2H), 3.52À3.56 (m, 2H) 3.67
(s, 3H); 13C NMR δ 173.8 (C), 51.4 (CH3), 44.7 (CH2), 33.7 (CH2),
32.1 (CH2), 26.3 (CH2), 24.1 (CH2).
3i:20g 1H NMR δ 3.92 (s, 3H), 7.41À7.57 (m, 3H), 8.01À8.04 (m,
2H); 13C NMR δ 167.1 (C), 132.9 (C), 128.6 (CH), 128.4 (CH), 128.2
(CH), 52.1 (CH3).
’ EXPERIMENTAL SECTION
3j:20d 1H NMR δ 2.31 (s, 3H), 3.81 (s, 2H), 7.13À7.15 (m, 2H)
7.83À7.85 (m, 2H); 13C NMR δ 167.1 (C), 143.5 (C), 129.5 (CH),
129.0 (CH), 127.4 (C), 51.9 (CH3), 21.6 (CH3).
General Methods. GC analysis was performed with a flame
ionization detector using a 0.22 mm  25 m capillary column (BP-5).
1H and 13C NMR were measured at 400 and 100 MHz, respectively, in
CDCl3 with Me4Si as the internal standard.
3k:20g 1H NMRδ3.85 (s, 3H), 7.33À7.36 (m, 2H) 7.90À7.93 (m, 2H);
13C NMR δ 166.2 (C), 139.4 (C), 131.0 (CH), 128.7 (CH), 128.5 (C),
52.2 (CH3).
Compounds 3a,20a 3b,17a 3c,20b 3d,20a 3e,20c 3f,20d 3g,20e 3h,20f 3i,20g
3j,20d 3k,20g 3l,20g 3m,17a 3n,20h 4a,15a 6a,20i 7a,20j 6b,20k 7b,20b 6c,20l
7c,20j 6d,20m and 7d20a were known compounds reported previously.
Typical Reaction Procedure for the Preparation of 3a
(Table 1, Entry 1). To a mixture of [Cp*IrCl2]2 (32 mg, 0.04 mmol),
Cs2CO3 (65 mg, 0.20 mmol), and MAE (9.6 mg, 0.12 mmol) were
added 1a (204 mg, 2.0 mmol), 2 (256 mg, 8.0 mmol), and acetone
(1.0 mL) under Ar. The reaction mixture was stirred at 25 °C for 24 h.
The conversions and yields of products were estimated from the peak
areas based on the internal standard technique using GC showed that 3a
was obtained in 84% yield. The product (3a) was isolated by column
3l:20g 1H NMR δ 3.79 (s, 3H), 3.82 (s, 3H), 7.84À7.86 (m, 2H)
7.92À7.94 (m, 2H); 13C NMR δ 166.9 (C), 163.3 (C), 131.6 (CH),
122.6 (C), 113.6 (CH), 55.4 (CH3), 51.9 (CH3).
3m:17a 1H NMR δ 3.55 (s, 2H), 3.61 (s, 3H), 7.17À7.27 (m, 5H);
13C NMR δ 172.0 (C), 133.9 (C), 129.2 (CH), 128.5 (CH), 127.1
(CH), 52.0 (CH3), 41.1 (CH2).
3n:20h 1H NMR δ 3.55 (s, 2H), 3.65 (s, 3H), 7.16À7.18 (m, 2H)
7.23À7.26 (m, 2H); 13C NMR δ 171.6 (C), 133.0 (C), 132.3 (C), 130.6
(CH), 128.7 (CH), 52.1 (CH3), 40.4 (CH2).
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NOTE
4a:15a 1H NMR δ 0.79À0.84 (m, 6H), 1.15À1.25 (m, 8H),
1.51À1.59 (m, 4H) 2.22 (t, J = 7.6 Hz, 2H) 3.99 (t, J = 6.6 Hz, 3H);
13C NMR δ 174.0 (C), 64.4 (CH2), 34.4 (CH2), 31.4 (CH2), 31.3
(CH2), 28.6 (CH2), 25.6 (CH2), 24.7 (CH2), 22.5 (CH2), 22.3 (CH2),
14.0 (CH3), 13.9 (CH3).
(5) Simon, E. S.; Young, M.; Chan, A.; Bao, Z.-Q.; Andrews, P. C.
Anal. Biochem. 2008, 377, 234 and references cited therein.
(6) Kusdiana, D.; Saka, S. Appl. Biochem. Biotechnol. 2004,
113À116, 781.
(7) (a) Danishefsky, S.; Hirama, M.; Gombatz, K.; Harayama, T.;
Berman, E.; Schuda, P J. Am. Chem. Soc. 1978, 100, 6536. (b) Otera, J.
Chem. Rev. 1993, 93, 1449 and references cited therein.
6a:20i 1H NMR δ 1.21À1.25 (m, 12H), 1.45À1.56 (m, 4H), 2.23 (t,
J = 7.6 Hz, 2H), 3.56 (t, J = 6.6 Hz, 2H), 3.56 (s, 3H); 13C NMR δ 174.3
(C), 62.9 (CH2), 51.4 (CH3), 34.0 (CH2), 32.7 (CH2), 29.3 (CH2),
29.3 (CH2), 29.1 (CH2), 29.0 (CH2), 25.6 (CH2), 24.9 (CH2).
6b:20k 1H NMR δ 1.30À1.33 (m, 6H), 1.54À1.64 (m, 4H), 2.30 (t,
J = 6.9 Hz, 2H), 3.62 (t, J = 6.6 Hz, 2H), 3.66 (s, 3H); 13C NMR δ 174.4
(C), 62.9 (CH2), 51.5 (CH3), 34.1 (CH2), 32.7 (CH2), 29.1 (CH2),
29.0 (CH2), 25.6 (CH2), 24.9 (CH2).
(8) (a) Seyferth, D.; Dow, A. W.; Menzel, H.; Flood, T. C. J. Am.
Chem. Soc. 1968, 90, 1080. (b) Hashimoto, N.; Aoyama, T.; Shioiri, T.
Chem. Pharm. Bull. 1981, 29, 1475. (c) Hirai, Y.; Aida, T.; Inoue, S. J. Am.
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6c:20l 1H NMR δ 1.30À1.33 (m, 8H), 1.54À1.62 (m, 4H), 1.90 (s,
1H) 2.31 (t, J = 7.6 Hz, 2H), 3.62 (t, J = 6.6 Hz, 2H), 3.67 (s, 3H); 13C
NMR δ 174.4 (C), 62.9 (CH2), 51.5 (CH3), 34.1 (CH2), 32.7 (CH2),
29.4 (CH2), 29.2 (CH2), 29.1 (CH2), 25.7 (CH2), 24.9 (CH2).
6d:20m 1H NMR δ 1.27À1.32 (m, 12H), 1.55À1.63 (m, 4H), 2.30 (t,
J = 7.6 Hz, 2H), 3.64 (t, J = 6.6 Hz, 4H), 3.67 (s, 3H); 13C NMR δ 174.4
(C), 63.1 (CH2), 51.5 (CH3), 34.1 (CH2), 32.8 (CH2), 29.59 (CH2),
29.56 (CH2), 29.5 (CH2), 29.4 (CH2), 29.24 (CH2), 29.15 (CH2), 25.7
(CH2), 25.0 (CH2).
7a:20j 1H NMR δ 1.21À1.26 (m, 8H), 1.52À1.56 (m, 4H), 2.23 (t, J =
7.3 Hz, 4H), 3.56 (s, 6H); 13C NMR δ 174.2 (C), 51.4 (CH3), 34.0
(CH2), 29.0(CH2), 28.9 (CH2), 24.8 (CH2).
7b:20b 1H NMR δ 1.32À1.34 (m, 4H), 1.61À1.63 (m, 4H), 2.30 (t,
J = 7.3 Hz, 4H), 3.67 (s, 6H); 13C NMR δ 174.2 (C), 51.5 (CH3), 34.0
(CH2), 28.8 (CH2), 24.8 (CH2).
7c:20j 1H NMR δ 1.30À1.35 (m, 6H), 1.60À1.63 (m, 4H), 2.30 (t, J =
7.3 Hz, 4H), 3.67 (s, 6H); 13C NMR δ 174.2 (C), 51.5 (CH3), 34.1
(CH2), 28.9 (CH2), 28.9 (CH2), 24.9 (CH2).
7d:20a 1H NMR δ 1.27À1.33 (m, 12H), 1.58À1.62 (m, 4H), 2.30 (t,
J = 7.6 Hz, 4H), 3.67 (s, 6H); 13C NMR δ 174.3 (C), 51.5 (CH3), 34.1
(CH2), 29.4 (CH2), 29.2 (CH2), 29.1 (CH2), 25.0 (CH2).
’ ASSOCIATED CONTENT
Supporting Information. Copies of 1H and 13C NMR of
S
b
the products. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
(18) When Cs2CO3, K3PO4, and KOH were used as base, we could
perform the reaction in homogeneous solution. Therefore, we concluded
the differences between the bases is not a result of different solubilities.
(19) Morita, K.; Nishiyama, Y.; Ishii, Y. Organometallics 1993, 12, 3748.
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C.; Rao, C. S. Org. Process Res. Dev. 2009, 13, 769. (e) Chavan, S. P.;
Ethiraj, K. S. Tetrahedron Lett. 1995, 36, 2281. (f) Hamed, O.; El-Qisairi,
A.; Henry, P. M. J. Org. Chem. 2001, 66, 180. (g) Yu, M.; Wen, W.; Wang,
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Corresponding Author
*E-mail:(Y.O.) obora@kansai-u.ac.jp; (Y.I.) r091001@kansai-u.ac.jp.
’ ACKNOWLEDGMENT
This work was supported by a Grant-in-Aid for Scientific
Research, “High-Tech Research Center” Project for Private
Universities (2005À2009), and the Strategic Project to Support
the Formation of Research Bases at Private Universities
(2009À2014): matching fund subsidy from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
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