Selective monoesterification of dicarboxylic acids catalysed by ion-exchange resins

Article abstract of DOI:10.1039/a902325i

Symmetrical dicarboxylic acids with 4-14 carbon atoms gave selectively the corresponding monoesters in high yields in the transesterification catalysed by strongly acidic ion-exchange resins in ester-hydrocarbon mixtures. It was found that the rate of the esterification of the dicarboxylic acids is much higher than that of the monocarboxylic acids formed. This result can explain the high selectivity for the monoester formation and can also be explained by the existence of an aqueous layer on the surface of the resins. This method of selective esterification is quite simple and practical. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a902325i

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Selective monoesterification of dicarboxylic acids catalysed by ion-
exchange resins
Takeshi Nishiguchi,*a Yasuhiro Ishiib and Shizuo Fujisakib
a Faculty of Agriculture, Yamaguchi University, Yamaguchi 753, Japan
b Department of Applied Chemistry and Chemical Engineering, Faculty of Engineering,
Yamaguchi University, Ube, Yamaguchi 755, Japan
Received (in Cambridge, UK) 23rd March 1999, Accepted 17th August 1999
Symmetrical dicarboxylic acids with 4–14 carbon atoms gave selectively the corresponding monoesters in high yields
in the transesterification catalysed by strongly acidic ion-exchange resins in ester–hydrocarbon mixtures. It was found
that the rate of the esterification of the dicarboxylic acids is much higher than that of the monocarboxylic acids
formed. This result can explain the high selectivity for the monoester formation and can also be explained by the
existence of an aqueous layer on the surface of the resins. This method of selective esterification is quite simple and
practical.
Introduction
Methods for the selective protection of one of two identical
functional groups, which exist in symmetrical positions in a
molecule, are important in organic synthesis. It is also worth
studying the preparation of monoesters of symmetrical diacids
when the cyclic anhydrides are not readily available. Dicarb-
oxylic acids have been reported to be selectively monoprotected
in a few ways. They give monomethyl esters in the reaction with
diazomethane or dimethyl sulfate in the presence of alumina or
silica gel.1 Methods to obtain monoesters via cyclic compounds
have been developed.2 Enzymatic methods to give monoesters
have been thoroughly reviewed.3 Monoesterification of diacids
using alkyl halides under phase-transfer catalysis4 and using
alcohols and acid catalysts such as sulfuric acid5 have also been
reported. Selective monoacylation of diols has been studied
more extensively.6
We have found that symmetrical diols are selectively mono-
acylated in ester–alkane7 and monotetrahydropyranylated in
dihydropyran–hydrocarbon mixtures8 in reactions catalysed
by acidic ion-exchange resins. These studies suggest that similar
selectivity appears in the reactions catalysed by wet ion-
exchange resins when the following conditions are fulfilled: (1)
the solubility in water decreases in the following order: starting
materials > monoprotected products > diprotected products
and/or the solubility in the organic solvents increases in the
reverse order, and (2) the dissolving power of the solvents is
appropriate. These results along with the fact that esterification
is often used to protect the carboxy group9 prompted us to
study the monoesterification of symmetrical dicarboxylic acids
by transesterification10 catalysed by sulfonic acid-type ion-
exchange resins (Scheme 1). A part of the results described in
Fig. 1 Yields vs. reaction time. Hexanedioic acid or hexanedioic acid
monobutyl ester (1 mmol) and Dowex 50WX2 (50–100 mesh) (1.0 g)
were stirred at 70 ЊC in HCO2Bu–octane (1:1, 10 cm3): monoester (᭹)
and diester (᭺) from the diacid; and the diester (ᮀ) from the monoester.
uct yields and the reaction period in the esterification of
hexanedioic acid. The acid (1 mmol) and Dowex 50WX2 (50–
100 mesh) (1.0 g) were stirred in butyl formate–octane (1:1, 10
cm3) at 70 ЊC. The yield of the monoester reached 91% when
that of the diester was 5%, and yields of the two esters did not
change so much even after the yield of the monoester reached a
maximum. These results show that the monoester reacts much
more slowly than the dicarboxylic acid and that the rate of the
formation of the diester does not increase very much even after
most of the dicarboxylic acid has been consumed. That the
yield of the diester does not increase rapidly even after most of
the dicarboxylic acid has been consumed is uncommon in an
ordinary successive reaction and enhances the value of this
reaction because the timing to terminate the successive esterifi-
cation is not so important.
Table 1 shows that all the symmetrical dicarboxylic acids
with 5–14 carbon atoms gave the corresponding monobutyl
esters in high yields in the transesterification catalysed by the
strongly acidic ion-exchange resin in butyl formate–octane mix-
tures. By the use of propyl formate and ethyl propionate instead
of butyl formate, hexanedioic acid yielded the corresponding
propyl and ethyl esters (Table 1, entries 8 and 9). These results
confirm the general applicability and practical utility of this
method. The reaction rates were lower in the reaction of
ion-exchange resin
HO2C–R1–CO2H
R2CO2R3–hydrocarbon
R3O2C–R1–CO2H ϩ [R3O2C–R1–CO2R3]
Scheme 1
this paper has been published as a preliminary report.11 This
method of monoesterification is quite simple and practical.
Results and discussion
Conditions for monoesterification
Fig. 1 shows an example of the relation between the prod-
J. Chem. Soc., Perkin Trans. 1, 1999, 3023–3027
This journal is © The Royal Society of Chemistry 1999
3023

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Table 1 Selective monoesterification of HO2C-R1-CO2H with R2CO2R3 catalysed by ion-exchange resina
Ester
Yield (%)
Entry
R1
R2
R3
%
T/ЊC
t/min
Monoester
Diester
1
2
3
cis-CH᎐CH-
H
H
H
Me
H
H
H
H
Et
H
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Pr
50
50
50
50
50
50
50
50
25
20
20
10
100
100
70
70
70
70
70
70
70
100
180
180
440
160
360
340
160
240
100
240
260
89
87
95
92
91
89
93
85
72
92
88
93
6
8
5
5
5
5
6
6
7
5
5
4
᎐
trans-CH᎐CH-
᎐
(CH2)3
(CH2)3
(CH2)4
(CH2)4
(CH2)4
(CH2)4
(CH2)4
(CH2)6
(CH2)6
(CH2)8
4
5
6b
7c
8
9
Et
10
11
12d
Bu
Bu
Bu
100
100
100
Me
H
13d
H
Bu
20
100
1020
89
5
14d
H
H
Bu
Bu
20
35
100
110
540
102
88
89
5
6
15d,e
16d
17d
18d
(CH2)12
(CH2)12
(CH2)12
H
H
Me
Bu
Bu
Bu
10
3
5
100
100
110
750
2340
1500
89
89
80
6
3
4
a Dicarboxylic acid (1.0 mmol) and Dowex 50WX2 (50–100 mesh) (1.0 g) were heated at 70 ЊC in an R2CO2R3–octane mixture (10 cm3). b The solvent
was the ester–benzene mixture. c The solvent was the ester–toluene mixture. d Amount of solvent was 20 cm3. e Amount of the catalyst 2.0 g.
soluble in the solvents than hexanedioic acid and that butyl
formate dissolves the dicarboxylic acids and the monoesters
more than octane does. The rate of monoesterification of
octanedioic acid varied in a similar way to the yields of the
monoester at a 5% yield of the diester. As will be described
later, it is presumed that the higher the percentage of butyl
formate in the mixed solvent, the lower the amount of the
dicarboxylic acids in the aqueous layer on the resin. The
decrease in the amount of dicarboxylic acids in the aqueous
layer is inferred to reduce the rate of monoester formation. This
inference may explain at least partly why the selectivity for
monoester formation was low when the percentage of butyl
formate in the solvent was very high.
The reaction in benzene and toluene was slower than that in
octane (Table 1, entries 6 and 7). This result may be elucidated
by the inference that the higher dissolving power of the aro-
matic solvents reduces the concentration of the diacids in the
aqueous layer.
Fig. 2 Yield and rate vs. solvent composition. Octanedioic acid or
In the reaction of the diacids having not more than six
hexanedioic acid (1 mmol) and Dowex 50WX2 (50–100 mesh) (1.0 g)
were stirred at 70 ЊC in HCO2Bu–octane (10 cm3): yield of the
monoester at 5% yield of the diester (᭹) and rate of monoester form-
ation (᭺) in the reaction of octanedioic acid. The yield (᭿) in the
reaction of hexanedioic acid.
carbon atoms, the amount of the solvent (butyl formate–
octane) hardly influenced the selectivity for monoester form-
ation. On the other hand, in the reaction of diacids having
more than eight carbon atoms, an increase in the amount of
solvent raised the selectivity.
butyl acetate than in that of butyl formate (Table 1, entries 4
and 11).
The amount of catalyst is very important. To realize high
selectivity in the esterification of dicarboxylic acids we need to
use more than about ten times as much ion-exchange resin as
we used in the selective acylation4 and tetrahydropyranylation5
of diols (Table 2).
To examine the performance of the catalysts, hexanedioic
acid and an ion-exchange resin were stirred at 70 ЊC in a mix-
ture of butyl formate and octane (1:1) (Table 3). Almost all the
sulfonic-type ion-exchange resins of wet types showed nearly
the same monoester selectivity as Dowex 50W. Dowex 50WX2
(50–100 mesh) lost 75% of its weight by being dried over P2O5.
The dried resin showed lower selectivity than the original resin.
The amounts of the wet and the dried catalysts were chosen
so that similar initial rates were obtained. The selectivity of
Each dicarboxylic acid has a peculiar butyl formate–octane
solvent ratio that gives the highest selectivity. Generally, the
larger the number of carbon atoms in a dicarboxylic acid, the
smaller the butyl formate:octane ratio to realize the highest
selectivity. Fig. 2 shows the relation between the composition of
solvents and the yields of the monoester at the yield of 5% of
the diesters in the reaction of octanedioic acid and hexanedioic
acid. The yields of the monoesters increased and then decreased
as the ratio of butyl formate rose in the solvent. The percent-
ages of butyl formate in the solvent at which the maximum
yields were attained were 20% and 50%. This result may be
explained partly by the inference that octanedioic acid is more
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Table 2 Amount of catalyst and selectivitya
Yield (%)c
Monoester
Amount of
catalyst/g
Yield
(%)b
Diester
0.2
0.4
1.0
1.6
2.0
3.0
16
44
85
85
83
79
53
61
89
87
85
80
44
15
9
6
6
7
a Hexanedioic acid (1.0 mmol) and Dowex 50WX2 (50–100 mesh) were
heated at 100 ЊC in HCO2Bu–octane (1:1, 10 cm3). b Yield of mono-
butyl ester at 5% yield of the diester. c Yields when amount of the
monoester reached a maximum.
Fig. 3 Yield and rate vs. amount of water. Hexanedioic acid (1 mmol)
Table 3 Selectivity and catalytic activity of ion-exchange resinsa
and dried Dowex 50WX2 (50–100 mesh) (0.2 g) and water were stirred
at 70 ЊC in HCO2Bu–octane (1:1, 10 cm3): yield of the monoester at 5%
yield of the diester (᭹) and rate of monoester formation (᭿). The yield
(᭺) and the rate (ᮀ) in the reaction catalysed by the original wet resin
(1.0 g) are also shown.
Yield
(%)b
Rate c/10Ϫ3
M minϪ1
Resin
Dowex 50WX2 (50–100 mesh)d
Dowex 50WX2 (50–100 mesh)d,e
Dowex 50WX2 (200–400 mesh)d
Dowex 50WX8 (200–400 mesh)f
Dowex 50WX4 (200–400 mesh)g
Dowex 50WX8 (50–100 mesh)f
Amberlite IR-120 (plus)
Amberlite IR-118 (H)
91
32
90
90
88
88
85
83
74
33
17
13
1.5
0.6
0.7
1.6
1.1
1.3
0.8
1.0
0.3
1.6
0.5
0.4
When the catalyst dried over P2O5 was used, the selectivity,
the rate of the formation of the monoester and the maximum
yield of the monoester were low (Table 2 and Fig. 3). When
increasing amounts of water were added to the reaction system
using the dried catalyst, the rate of monoester formation rose,
exhibited maximum values, and then declined (Fig. 3). The
yield of the monoester at the 5% yield of the diester rose at
first and then became nearly constant. It was also found
that the amount of the water contained in the original Dowex
50W was suitable for the high selectivity and reactivity. These
results support at least in part the proposed mechanism noted
before.
Hexanedioic acid and hexanedioic acid monobutyl ester were
stirred in a vessel containing water and butyl formate–octane
mixture in the absence of catalysts. The monoester hardly
existed in the water layer, while the diacid did mostly. The
higher the percentage of butyl formate in the organic layer, the
lower the amount of the diacid in the water layer. On the basis
of the model experiment it is inferred that the concentration of
butyl formate in the water layer of the catalysts increases and
the concentration of diacids decreases when the ratio of butyl
formate in the solvent rises. This inference seems to explain at
least in part the result that the selectivity and the reaction rate
first increased and then decreased as the percentage of butyl
formate in the solvent was elevated (Fig. 2), for the transesterifi-
cation is supposed to occur in the water layer of the catalysts
and/or the interface between the water layer and the organic
layer.
Amberlyst 15 (wet)
Amberlyst 15h
Amberlyst XN-1010h
Nafion NR-50h
a Hexanedioic acid (1 mmol) and a resin (1.0 g) were heated at 70 ЊC in
HCO2Bu–octane (1:1, 10 cm3). b Yield of the monoester at 5% yield
of the diester. c Initial rate of monoester formation. d 2% cross-linking.
e Dried resin (0.2 g) was used. f 8% Cross-linking. g 4% Cross-linking.
h For non-aqueous application.
Nafion, Amberlyst 15, Amberlyst XN-1010 which are for non-
aqueous application and inferred to contain little water, was
low. This result also shows that a certain amount of water in the
resins is essential for the high selectivity. The carboxylic acid-
type resin (Amberlite IRC-50) was inactive. Dowex 50WX2
(50–100 mesh) was used in all the esterification described here-
after because it dispersed most easily in the solutions.
Rationalization of the selectivity
Fig. 1 also shows the yield of the diester in the reaction of
hexanedioic acid monobutyl ester (starting material). Condi-
tions of this reaction were the same as those of the esterification
of the diacid noted in Fig. 1. The yields of the diester in the
reaction of the monoester (starting material) were much lower
than the yields of the monoester in the reaction of the diacid.
This outcome shows that the diacid reacted much more rapidly
than the monoester to realize the selective formation of the
monoester from the diacid.
We presume that the selectivity arises from the factors
enumerated below. (1) An acidic water layer is formed on the
surface of the resins, because the sulfonic acid-type ion-
exchange resins usually contain 50–80% water.12 (2) A partition
equilibrium between the aqueous layer and the aprotic ester–
hydrocarbon layer is setup, and the ratios of the dicarboxylic
acids in the water layer are much higher than those of the
formed monoesters. (3) The diacids react in preference to the
monoesters in the aqueous layer and/or at the interface between
the aqueous and the nonaqueous liquid layer. (4) The mono-
esters move from the aqueous layer into the organic layer, which
does not contain catalytic protons, and remain there without
reacting further.
Experimental
Reagents and solvents were purchased and used without purifi-
cation. GLC analyses were performed on an instrument with an
autoinjector. The column was a 30 m × 0.25 mm i.d. fused silica
capillary column coated with NEUTRABOND-5.
An example of monoesterification of symmetrical dicarboxylic
acids for analytical purposes
A mixture of hexanedioic acid (0.146 g, 1 mmol), Dowex
50WX2 (50–100 mesh) (1.0 g), pentadecane (GLC internal
standard, 0.02 cm3), and butyl formate–octane (1:1 (v/v), 10
cm3) was stirred at 70 1 ЊC. Samples of the supernatant liquid
were then removed periodically and analysed by GLC.
The retention times of the monoester and the diester were
identical to those of authentic samples prepared by the con-
ventional method.
J. Chem. Soc., Perkin Trans. 1, 1999, 3023–3027
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The yields of monoesters at a particular yield of diesters were
derived from plots of product yield vs. time, such as that shown
in Fig. 1.
Tetradecanedioic acid dibutyl ester.14,23 1H NMR δ 0.93 (t,
6H), 1.26–1.45 (m, 20H), 1.55–1.63 (m, 8H), 2.26–2.31 (t, 4H),
4.04–4.09 (t, 4H).
Butyl esters of maleic acid and fumaric acid are mentioned in
many reports.27 A number of papers referred to dipropyl ester
and diethyl ester of hexanedioic acid.14,15,28
An example of monoesterification of symmetrical dicarboxylic
acids for preparative purposes
Hexanedioic acid (0.73 g, 5.0 mmol) and Dowex 50WX2 (50–
100 mesh) (5.0 g) were stirred at 70 1 ЊC in a mixture of butyl
formate (25 cm3) and octane (25 cm3) and the mixture was
monitored by GLC. After 3 h the catalyst was removed by fil-
tration and the solution was evaporated. The residue was
chromatographed with hexane–EtOAc (4:1) on a silica gel
column to give hexanedioic acid monobutyl ester13 (0.82 g,
85%) and hexanedioic acid dibutyl ester14–16 (0.05 g, 3%). The
Drying of ion-exchange resin
Dowex 50WX2 (50–100 mesh) (1 g) was kept over P2O5 (30 g) in
a desiccator. The weight of the resin decreased to 26% in 1 day
and 25% in 7 days. The resin dried for 7 days was used in the
transesterification.
Esterification catalysed by the dried resin and water
1
monoester: Rf = 0.29 in hexane–EtOAc (4:1); H NMR (270
A mixture of hexanedioic acid (0.146 g, 1 mmol), the dried
Dowex 50WX2 (50–100 mesh) (0.2 g), pentadecane (GC
internal standard, 20 µl), water, and butyl formate–octane
(1:1 (v/v), 10 cm3) was stirred at 70 1 ЊC. Samples of the
supernatant organic layer were then removed periodically and
analysed by GLC.
MHz, CDCl3) δ 0.93 (t, 3H), 0.91–0.96 (t, 3H), 1.31–1.45 (m,
2H), 1.56–1.74 (m, 6H), 2.30–2.42 (m, 4H), 4.05–4.10 (t, 2H).
1
The diester: Rf = 0.58 in 20% EtOAc–hexane; H NMR δ 0.93
(t, 6H), 1.30–1.45 (m, 4H), 1.55–1.74 (m, 8H), 2.25–2.36 (m,
4H), 4.08 (t, 4H).
Pentanedioic acid monobutyl ester.17,18 1H NMR δ 0.93 (t,
3H), 1.31–1.45 (m, 2H), 1.56–1.64 (m, 2H), 1.90–2.01 (m, 2H),
2.37–2.46 (m, 4H), 4.08 (t, 2H).
Distribution of dicarboxylic acid and monoester in aqueous layer
Hexanedioic acid (0.073 g), hexanedioic acid monobutyl
ester (0.107 g), pentadecane (0.01 cm2), water (0.4 cm3), and
HCO2Bu–octane (5 cm3) were stirred for 10 min at 70 ЊC. The
organic layer and the water layer were injected into the GLC.
When the percentages of HCO2Bu in the organic layer were 20,
40 and 60%, the percentages of the diacid in the water layer
were 94, 86 and 62%. The percentages of the monoester in the
water layer were less than 1% in all the conditions examined.
Pentanedioic acid dibutyl ester.19,20 1H NMR δ 0.93 (t, 6H),
1.31–1.45 (m, 4H), 1.58–1.66 (m, 4H), 1.89–2.00 (m, 2H), 2.37
(t, 4H), 4.08 (t, 4H).
Hexanedioic acid monopropyl ester.21 1H NMR δ 0.94 (t, 3H),
1.58–1.74 (m, 6H), 2.29–2.42 (m, 4H), 4.03 (t, 2H).
Hexanedioic acid monoethyl ester.22 1H NMR δ 1.26 (t, 3H),
1.62–1.76 (m, 4H), 2.29–2.42 (tt, 4H), 4.07 (t, 2H).
References
1 H. Ogawa, Y. Ichimura, T. Chihara, S. Teratani and K. Taya, Bull.
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and K. Taya, Bull Chem. Soc. Jpn., 1988, 61, 2383.
2 K. Matoba and T. Yamazaki, Chem. Pharm. Bull., 1983, 31, 2955;
B. Rigo, D. Fasseur, P. Cauliez and D. Couturier, Tetrahedron
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D. Belotti, V. Bellosta and D. Brocca, Tetrahedron Lett., 1994, 35,
6089.
3 H. J. Gais, in Enzyme Catalysis in Organic Synthesis, ed. K. Drauz
and H. Waldmann, VCH, Weinheim, 1995, Section B, ch. 1, p. 178.
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M. C. Tedford, Tetrahedron, 1990, 48, 6587; A. M. Klibanov, Acc.
Chem. Res., 1990, 23, 114; E. Ozaki, T. Uragaki, K. Sakasita and
A. Sakima, Chem. Lett., 1995, 539 and references cited therein.
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(1992) (Chem. Abstr., 1993, 118, 124071y).
6 T. Nishiguchi, K. Kawamine and T. Ohstuka, J. Org. Chem., 1992,
57, 312; H. Ogawa, M. Amano and T. Chihara, Chem. Commun.,
1998, 495; G. W. Breton, J. Org. Chem., 1997, 62, 8952; H. Ogawa,
M. Amano, T. Chihara, S. Teratani and K. Taya, J. Chem. Soc.,
Chem. Commun., 1986, 1337; J. H. Babler and M. J. Coghlan,
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1
Octanedioic acid monobutyl ester. H NMR δ 0.923 (t, 3H),
1.33–1.41 (m, 6H), 1.57–1.67 (m, 6H), 2.28–2.37 (tt, 4H), 4.07
(t, 2H); 13C NMR (CDCl3) δ 13.7, 19.1, 24.5, 24.7, 28.7, 28.7,
30.7, 33.8, 34.3, 64.2, 173.9, 179.1; IR (film, cmϪ1) 2959, 2936,
2871, 2671, 1736 (C᎐O), 1709 (C᎐O), 1464, 1416, 1244, 1179,
᎐
᎐
1136, 1092, 1021, 942, 738.
Octanedioic acid dibutyl ester.14,15,19,23,24 1H NMR δ 0.93 (t,
6H), 1.31–1.42 (m, 8H), 1.55–1.65 (m, 8H), 2.28 (t, 4H), 4.06
(t, 4H).
Decanedioic acid mono butyl ester.25 1H NMR δ 0.93 (t, 3H),
1.31–1.45 (m, 10H), 1.56–1.65 (m, 6H), 2.23–2.37 (tt, 4H), 4.07
(t, 2H).
1
trans-Cyclohexane-1,2-dicarboxylic acid monobutyl ester. H
NMR δ 0.92 (t, 3H), 1.24–1.43 (m, 6H), 1.56–1.61 (m, 2H),
1.79–1.81 (m, 2H), 2.06–2.18 (m, 2H), 2.57–2.64 (m, 2H), 4.06–
4.10 (t, 2H); 13C NMR (400 MHz, CDCl3) δ 13.6, 19.0, 25.2,
25.2, 28.8, 28.9, 30.6, 44.5, 44.6, 64.4, 175.0, 180.9.
cis-Cyclohexane-1,2-dicarboxylic acid monobutyl ester.17 1H
NMR δ 0.92 (t, 3H), 1.34–1.49 (m, 6H), 1.56–1.63 (m, 2H),
1.77–1.80 (m, 2H), 2.00–2.05 (m, 2H), 2.84–2.85 (m, 2H), 4.07–
4.11 (t, 2H); 13C NMR δ 13.6, 19.1, 23.6, 23.8, 26.0, 26.4, 30.5,
30.9, 42.5, 64.4, 173.6, 179.3.
trans-Cyclohexane-1,4-dicarboxylic acid monobutyl ester.26
1H NMR δ 0.93 (t, 3H), 1.33–1.59 (m, 6H), 1.60–1.64 (m, 2H),
2.06–2.10 (m, 4H), 2.27–2.33 (m, 2H), 4.06 (t, 2H); 13C NMR
δ 13.7, 19.1, 27.8, 27.9, 30.7, 30.9, 42.1, 42.5, 64.3, 96.1, 175.5,
180.5.
7 T. Nishiguchi, S. Fujisaki, Y. Ishii, Y. Yano and A. Nishida, J. Org.
Chem., 1994, 59, 1191.
8 T. Nishiguchi, S. Fujisaki, M. Kuroda, K. Kajisaki and M. Saitoh,
J. Org. Chem., 1998, 63, 8183.
9 T. W. Greene and P. G. M. Wuts, Protecting Groups in Organic
Synthesis, 2nd edn., Wiley, New York, 1991; P. J. Kocienski,
Protecting Groups, Georg Thieme Verlag, Stuttgart, 1994.
10 J. Otera, Chem. Rev., 1993, 93, 1449.
11 M. Saitoh, S. Fujisaki, Y. Ishii and T. Nishiguchi, Tetrahedron Lett.,
1996, 37, 6733.
1
Tetradecanedioic acid monobutyl ester. H NMR δ 0.93 (t,
3H), 1.16–1.45 (m, 18H), 1.55–1.78 (m, 6H), 2.26–2.38 (tt, 4H),
4.07 (t, 2H).
3026
J. Chem. Soc., Perkin Trans. 1, 1999, 3023–3027

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