Synthesis and N-Alkylation of 2-Alkyl-and 2-Arylimidazole-4,5-dicarboxylic acid esters

Article abstract of DOI:10.1134/S1070363207050234

Nitration of d-tartaric acid, followed by treatment of the resulting dinitrotartaric acid with ammonia and aldehydes gave 2-phenyl-, 2-(2-pyridyl)-, 2-isopropyl-, and 2-isobutylimidazole-4,5-dicarboxylic acids. Some factors affecting the yield of the fina

Full text of DOI:10.1134/S1070363207050234

ISSN 1070-3632, Russian Journal of General Chemistry, 2007, Vol. 77, No. 5, pp. 949 953.
Original Russian Text A.V. Lebedev, A.B. Lebedeva, V.D. Sheludyakov, E.A. Kovaleva, O.L. Ustinova, V.V. Shatunov, 2007, published in Zhurnal
Obshchei Khimii, 2007, Vol. 77, No. 5, pp. 855 859.
Pleiades Publishing, Ltd., 2007.
Synthesis and N-Alkylation of 2-Alkyl-
and 2-Arylimidazole-4,5-dicarboxylic Acid Esters
A. V. Lebedev, A. B. Lebedeva, V. D. Sheludyakov,
E. A. Kovaleva, O. L. Ustinova, and V. V. Shatunov
State Research Institute of Chemistry and Technology of Organometallic Compounds,
sh. Entuziastov 38, Moscow, 111123 Russia
e-mail: vdsh2004@yandex.ru
Received November 8, 2006
Abstract Nitration of D-tartaric acid, followed by treatment of the resulting dinitrotartaric acid with
ammonia and aldehydes gave 2-phenyl-, 2-(2-pyridyl)-, 2-isopropyl-, and 2-isobutylimidazole-4,5-dicarboxylic
acids. Some factors affecting the yield of the final products were revealed, and optimal conditions for their
esterification were found. N-Alkylation of 2-substituted imidazole-4,5-dicarboxylates thus obtained involves
considerable steric hindrances; therefore, the corresponding N-alkyl derivatives can be obtained in a poor yield
only in the presence of such a strong base as 1,8-diazabicyclo[5.4.0]undec-7-ene.
DOI: 10.1134/S1070363207050234
It is known [1 3] that O,O -dinitrotartaric acid II
(2,3-dinitroxybutanedioic acid) obtained by nitration
of D-tartaric acid (I) reacts with ammonia and alde-
hydes IVa, IVe, and IVf to give 2-substituted imida-
zole-4,5-dicarboxylic acids Va, Ve, and Vf, respec-
tively. Analogous reaction with formaldehyde leads
to unsubstituted imidazole-4,5-dicarboxylic acid; it
was shown [4, 5] that this reaction involves inter-
mediate formation of , -dioxosuccininc acid (III).
Taking into account the known ability of imidazole-
4,5-dicarboxylic acid esters to undergo alkylation at
the nitrogen atom [6], it seemed to be interesting to
synthesize various derivatives of 2-alkyl- and 2-aryl-
imidazole-4,5-dicarboxylates via alkylation with di-
haloalkanes VIII (X = Br, Y = Cl, n = 2, 3); the
subsequent variation of the Y substituent in com-
pounds IX and X (Y = Cl
I
NHR2) could make it
possible to effect cyclization at the ester moiety and
obtain new heterocyclic compounds like XI. The
present communication reports on the results of our
attempts to synthesize a wide series of 2-substituted
imidazole-4,5-dicarboxylates VI and VII and effect
their N-alkylation to obtain derivatives IX and X.
The nitration of D-tartaric acid with a mixture of
nitric and sulfuric acids at 0 C, followed by treatment
(1) NH3
CHOH
CHOH
C=O
CHOH
CHOH
CHOH
CHOH
COOH
(2) R1CHO (IVa IVf)
HOOC
HN
HNO3/H2SO4
CHONO2
CHONO2
CHOH
(3) HCl
N
C=O
R1
CHOH
I
II
III
Va Vf
COOR2
COOR2
R2OOC
COOR2
R2OOC
O
(1) SOCl2/R2OH
(2) R2ONa
Y = Cl, I, NHR3
NR3
X(CH2)nY (VIII)
HX
N (CH2)n
Y
--------------
N
N
N
HN
R2OH
(CH2)n 1
N
R1
IXa IXf, Xa Xf
R1
R1
VIa VIf, VIIa VIIf
XI
R1 = Ph (a), (CH3)2CH (b), (CH3)2CHCH2 (c), 2-pyridyl (d), MeOCO(CH2)6 (e), Me (f); VI, IX, R2 = Et; VII, X,
R2 = Me.
949

950
LEBEDEV et al.
of the reaction mixture with excess ammonia at
5
The reactions of acids Va Vd with 2 equiv of
thionyl chloride in anhydrous ethanol or methanol
gave dicarboxylic ester hydrochlorides VIa VId and
VIIa in 98 99% yield. Free bases VIa VId were
isolated by treatment with anhydrous potassium
carbonate in the corresponding alcohol or with 12%
aqueous sodium carbonate on cooling. In both cases, a
considerable amount of alcohol was required, and the
yields of the free bases did not exceed 80%. The best
results (yield 98 99%) were obtained using a con-
centrated solution of sodium ethoxide or methoxide
in ethanol or methanol, respectively. This procedure
can be performed just before treatment of esters VIa
VId and VIIa with alkylating agents. The proposed
method for the esterification of diacids Va Vd is
simpler and more effective that the known procedure
involving treatment of imidazoledicarboxylic acid
with an alcoholic solution of hydrogen chloride [6, 7].
to 10 C and an equimolar amount of aldehyde IVa
or IVd or 2 equiv of aldehyde IVb or IIc at 0 C, led
to the formation of 2-aryl- and 2-alkylimidazole-4,5-
dicarboxylic acids Va Vd in 47, 27, 21, and 17.6%
yield (calculated on the initial tartaric acid), respec-
tively. The products are colorless (Va Vc) or green
(Vd) crystalline substances which decompose above
257 C. The synthesis of compounds Va Vd is
laborious but well reproducible; however, no more
than 46 g of the above acids (for imidazole Va) can be
prepared at once in a 2-l flask.
The structure of compounds was confirmed by the
1
data of elemental analysis and mass and H NMR
spectra. Acids Va Vd showed in the mass spectra the
molecular ion peaks whose fragmentation involved
successive elimination of two carbon(IV) oxide
molecules (for aromatic derivatives Va and Vd) or
elimination of the alkyl substituent followed by
simultaneous expulsion of two CO2 molecules (for
It should be noted that esterification of acids Va
Vc gives the corresponding esters VIa VIc and VIIa
as monohydrochlorides despite the presence of alkyl
substituent in position 2, which enhances the
basicity of the imidazole nitrogen atoms. On the other
hand, pyridyl-substituted derivative VId was isolated
as trihydrochloride, though the basicity of the imida-
zole nitrogen atoms therein is weakened due to con-
jugation with the pyridine ring.
1
2-alkyl derivatives Vb and Vc). In the H NMR spec-
tra of Va Vd we observed signals from protons in the
substituent on C2, a signal from one acid OH proton,
and a broadened signal from the NH proton and the
second OH group; the latter signal is broadened due to
exchange with water present in the solvent.
The different yields of compounds Va Vd may be
interpreted in terms of various factors. One of these is
the stability of aldehydes IVa IVd to oxidation to
carboxylic acids under the reaction conditions. Among
the aldehydes used, pyridine-2-carbaldehyde (IVd) is
the least stable, and the yield of the corresponding
diacid Vd is the lowest. Other factors may be the rate
of formation of imines in the reaction of dioxosuc-
cinic acid (III) with ammonia, their solubility, and
possible polymerization during the process. For ex-
ample, isobutyraldehyde (IVb) with ammonia forms
insoluble imine trimer; as a result, the yield of Vb
sharply decreases. Therefore, compound Vb was syn-
thesized using excess aldehyde IVb which was slowly
added to the reaction mixture under vigorous stirring.
Preliminary mixing of the aldehyde with an ammonia
solution completely inhibited the formation of
imidazole Vb. The use of excess aldehyde is also
desirable in the reactions with accessible aldehydes
that give rise to water-soluble imines.
Taking into account that the maximal yields of
imidazoledicarboxylic acid esters (calculated on the
initial tartaric acid) were obtained using the substrates
derived from most accessible aldehydes, just com-
pounds VIa, VIb, and VIIa were subjected to alkyla-
tion. The products were analyzed by NMR spectro-
scopy and gas chromatography mass spectrometry
(GC MS), and initial esters VIa, VIb, and VIIa were
isolated from the reaction mixtures. The following
alkylating systems were used: (a) 1 equiv of EtONa,
1 2 equiv of dihaloalkane VIIIa (X = Br, Y = Cl, n =
2), ethanol, 80 C, 24 h; and (b) 1.5 equiv of K2CO3,
2 equiv of VIIIa, DMF, 110 C, 16 h. In no case
alkylation was observed. We also tried to perform
theoretically possible addition of VIa to oxirane
(which was either passed through the reactions mix-
ture or generated in situ from ethylenebromohydrin),
vinyl chloride, and vinyl acetate. Typical procedures
were as follows: (a) a slight stream of oxirane was
bubbled until complete saturation through a 10% solu-
tion of compound VIa in methanol or THF containing
1 2 drops of water or 3 equiv of oxirane was conti-
nuously bubbled through the solution for 2 h at 25 C
and for 4 h at 55 C; (b) 2-bromoethanol (VIIIb, X =
Br, Y = OH, n = 2), 3 equiv, was added dropwise to
a 8% solution of 1 equiv of VIIa and 3 equiv of so-
dium methoxide in methanol, and the mixture was
Dicarboxylic acids Va Vd were formed initially
as the corresponding ammonium salts which were
converted into the free acids by treatment with hydro-
chloric acid. The latter procedure should be performed
slowly under vigorous stirring since the reaction
mixture is heterogeneous and residual dinitrotartaric
acid is very sensitive to HCl.
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SYNTHESIS AND N-ALKYLATION OF 2-ALKYL-
951
stirred for 2 h at 25 C, for 2 h at 50 C, and for 4 h
under reflux; (c) vinyl chloride was bubbled for 2 h at
20 C and for 4 h at 60 C through a 10% solution of
VIIa in THF containing 1 ml of acetic acid; and (d) a
mixture of 1 equiv of VIIa, 6 equiv of vinyl acetate
(freshly distilled, nonstabilized), and 1 ml of acetic
acid in THF was heated for 10 h. After removal of
volatile substances under reduced pressure, the residue
vigorous stirring, maintaining the temperature below
40 C, and the mixture was left to stand for 2 h in an
ice bath. The precipitate was filtered on Buchner
funnel through glass fiber with protection from
atmospheric moisture and thoroughly squeezed over a
period no longer than 25 min. The precipitate was
immediately transferred into a porcelain beaker
containing 850 g of a finely crushed ice, cooled to
about 18 C, under continuous stirring with a por-
celain spoon. The resulting solution with a tempera-
ture of about 10 C was quickly transferred into a 2-l
flask, and neutralized with a concentrated ammonia
solution ( 460 ml) under vigorous stirring and cooling
with an acetone solid CO2 bath. When the pH value
attained 7 8, the cooling bath was removed, 140 ml of
an ammonia solution and 0.4 mol of freshly distilled
aldehyde IVa or IVd or 0.8 mol of aldehyde IVb or
IVc were added, and the mixture was stirred for 20 h
at 4 to 0 C. The mixture was carefully acidified with
concentrated hydrochloric acid (about 90 100 ml) to
pH 3 so as to avoid ejection of the reaction mixture
with evolved gases (voluminous foam). In the syn-
thesis of compound Vd, the mixture was neutralized
with hydrochloric acid to pH 7 and was then acidified
with acetic acid to pH 5.5. The mixture was filtered,
and the mother liquor was immediately utilized as
waste. The precipitate was washed with 500 ml of
water and 100 ml of cold isopropyl alcohol and dis-
persed in 400 ml of diethyl ether. The suspension was
stirred for 0.5 h, and the precipitate was filtered off
and dried at 80 100 C. We thus obtained pure (98
99%) crystalline compounds Va Vd in 47, 27, 21,
and 17.6% yield, respectively. The maximal yield of
Va was 46 48 g. The procedure can be scaled up
maximally to a 5-l flask (restriction at the neutraliza-
tion step); however, in this case, the real time of the
process considerably increases.
1
was analyzed by H NMR spectroscopy; in all cases,
only unreacted initial imidazole VIa or VIIa was
detected.
The low reactivity of 2-substituted imidazole-4,5-
dicarboxylic acid esters toward alkylating agents is
likely to result from steric hindrances: Both nitrogen
atoms in small imidazole ring are sterically shielded
by three substituents in positions 2, 4, and 5. We
succeeded in effecting N-alkylation of compounds
VIa and VIIa only in the presence of 1.1 equiv of
such a strong base as 1,8-diazabicyclo[5.4.0]undec-7-
ene (DBU) using 7 equiv of dihaloalkane VIIIa in
acetonitrile (80 C, 27 h) or DMF (110 C, 24 h). Ac-
1
cording to the H NMR data, 35% of IXa (n = 2,
Y = Cl) and 27% of Xa (n = 2, Y = Cl) (MeCN) or
42% of IXa and 40% of Xa (DMF) were formed from
1 equiv of ester VIa or VIIa, respectively. The reac-
tion in DMF was accompanied by considerable tarring.
By column chromatography on silica gel (hexane
benzene, 4:1) we succeeded in isolating compounds
IXa and Xa in 18 and 11% yield, respectively (in the
reaction performed in acetonitrile). Presumably, the
alkylation process includes deprotonation of imidazoles
VIa and VIIa by the action of DBU, and the resulting
anions are more reactive than the neutral molecules.
However, the poor yield of the alkylation products
(less than 10% on the initial tartaric acid) strongly
complicates search for synthetic approaches to hetero-
cycles XI, and further studies on the activation of
imidazolecarboxylic esters toward electrophiles are
necessary.
2-Phenylimidazole-4,5-dicarboxylic acid (Va).
1
Decomposition point 265 C. H NMR spectrum,
,
ppm: 4.0 br.s (NH, COOH), 7.44 m (3H, Harom),
8.16 d (2H, Harom), 19.78 (1H, COOH). Mass spec-
EXPERIMENTAL
trum, m/z: 232 [M]+ , 188 [M
CO2]+, 170 [M
CO2 H2O]+, 144 [M 2CO2]+. Found, %: C 57.02;
1
The H NMR spectra were measured on a Bruker
H 3.44. C11H8N2O4. Calculated, %: C 56.90; H 3.47.
AM-360 spectrometer at 360.14 MHz using DMSO-d6
as solvent and reference. The mass spectra (electron
impact, 70 eV) were recorded on a MAT-311A spec-
trometer with direct sample admission into the ion
source.
2-Isopropylimidazole-4,5-dicarboxylic acid (Vb).
1
Decomposition point 269 C. H NMR spectrum,
,
ppm: 1.31 d (6H, CH3), 3.26 m (1H, CH), 4.5 br.s
(NH, COOH), 19.70 (1H, COOH). Mass spectrum,
m/z: 198 [M]+ , 165 [M CH3 H2O]+, 156 [M + H
C3H7]+, 138 [M C3H7 OH]+, 110 [M 2CO2]+.
Found, %: C 48.58; H 5.12. C8H10N2O4. Calculated,
%: C 48.49; H 5.09.
2-Aryl- and 2-alkylimidazole-4,5-dicarboxylic
acids Va Vd (general procedure). A 1-l flask was
charged with 60 g of powdered D-tartaric acid,
130 ml of 70% nitric acid and 130 ml of 98% nitric
acid were added in succession, 240 ml of concentrated
sulfuric acid was quickly added dropwise under
2-Isobutylimidazole-4,5-dicarboxylic acid (Vc).
1
Decomposition point 257 C. H NMR spectrum,
,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 77 No. 5 2007

952
LEBEDEV et al.
ppm: 0.83 d (6H, CH3), 2.00 m (1H, CH), 2.44 d (2H,
CH2), 7.4 br.s (NH, COOH), 19.68 (1H, COOH).
Mass spectrum, m/z: 212 [M]+ , 179 [M CH3 H2O]+,
170 [M + H C3H7]+, 165 [M 2CH3 OH]+, 152
[M C3H7 OH]+, 124 [M 2CO2]+. Found, %: C
51.04; H 5.74. C9H12N2O4. Calculated, %: C 50.94;
H 5.70.
Diethyl 2-isopropylimidazole-4,5-dicarboxylate
(VIb). mp 188 190 C. 1H NMR spectrum, , ppm:
1.26 d (6H, CH3), 1.27 t (6H, CH3), 3.10 m (1H, CH),
4.27 q (4H, OCH2), 13.10 (1H, NH). Mass spectrum:
m/z 254 [M]+ . Found, %: C 56.74; H 7.16.
C12H18N2O4. Calculated, %: C 56.68; H 7.13. Hydro-
1
chloride: mp 98 105 C. H NMR spectrum, , ppm:
1.25 d (6H, CH3), 1.28 t (6H, CH3), 3.17 m (1H, CH),
4.27 q (4H, OCH2), 7.32 t (2H, NH+2). Found, %: C
49.32; H 6.68. C12H19ClN2O4. Calculated, %: C
49.57; H 6.59.
2-(2-Pyridyl)imidazole-4,5-dicarboxylic acid
(Vd). Decomposition point 270 C. 1H NMR spectrum,
, ppm: 3.8 br.s (NH, COOH), 7.43 t (1H, Harom),
7.92 t (1H, Harom), 8.10 d (1H, Harom), 8.63 d (1H,
Harom), 19.80 (1H, COOH). Mass spectrum, m/z: 233
[M]+ , 189 [M CO2]+, 171 [M CO2 H2O]+, 145
[M 2CO2]+. Found, %: C 51.63; H 3.06. C10H7N3O4.
Calculated, %: C 51.51; H 3.03.
Diethyl 2-isobutylimidazole-4,5-dicarboxylate
1
(VIc) hydrochloride. mp 95 100 C. H NMR spec-
trum, , ppm: 0.87 d (6H, CH3), 1.29 t (6H, CH3),
2.08 m (1H, CH), 2.66 d (2H, CH2), 4.29 q (4H,
OCH2), 7.32 t (2H, NH+2). Found, %: C 51.06; H 7.04.
C13H21ClN2O4. Calculated, %: C 51.23; H 6.94.
Esterification of dicarboxylic acids Va Vd
(general procedure). Thionyl chloride, 0.2 mol, was
added dropwise to a suspension of 0.05 mol of com-
pound Va Vd in 100 ml of anhydrous ethanol or
methanol (the mixture spontaneously warmed up to
45 55 C), and the mixture was heated for 1.5 2.5 h
under reflux until it became homogeneous. The mix-
ture was then evaporated under reduced pressure, the
residue was treated with 100 150 ml of anhydrous
diethyl ether, and the precipitate of VIa VId or VIIa
hydrochloride was filtered off and dried under reduced
pressure. Yield almost quantitative. To isolate free
bases VIa VId and VIIa, the corresponding hydro-
chloride was added under vigorous stirring to a con-
centrated solution of a required amount of sodium
ethoxide or methoxide in ethanol or methanol, res-
pectively. The mixture was evaporated, and the re-
sidue was washed with water and dried under reduced
pressure. The yields of pure compounds VIa VId and
VIIa were 98 99%. Alternatively, a 12% solution of
sodium carbonate was added dropwise to an alcoholic
solution of the corresponding hydrochloride to attain
pH 4 5, maintaining the temperature below 12 C. The
mixture was evaporated by half and cooled to 5 C.
The free bases separated as difficultly crystallizable
oils; they crystallized only after treatment with cold
diethyl ether. The yields did not exceed 80%.
Diethyl 2-(2-pyridyl)imidazole-4,5-dicarboxylate
1
(VId) trihydrochloride. mp 110 116 C. H NMR
spectrum, , ppm: 1.30 t (6H, CH3), 4.28 q (4H,
OCH2), 7.36 t (4H, NH+2, NH+), 7.54 t (1H, Harom),
8.03 t (1H, Harom), 8.18 d (1H, Harom), 8.70 d (1H,
Harom). Found, %: C 41.93; H 4.70. C14H18Cl3N3O4.
Calculated, %: C 42.18; H 4.55.
Dimethyl 2-phenylimidazole-4,5-dicarboxylate
1
(VIIa). mp 204 207 C. H NMR spectrum, , ppm:
3.84 s (6H, OCH3), 7.48 m (3H, Harom), 8.08 d (2H,
Harom), 13.75 (1H, NH). Mass spectrum, m/z: 260
[M]+ . Found, %: C 59.91; H 4.68. C13H12N2O4.
Calculated, %: C 60.00; H 4.65.
Alkylation of 2-substituted imidazole-4,5-di-
carboxylic acid esters (general procedure). A mix-
ture of 0.05 mol of ester VIa or VIIa, 0.055 mol of
DBU, and 0.35 mol of bromide VIIIa in 100 ml of
acetonitrile or DMF was stirred for 27 h at the boiling
point (in acetonitrile) or for 24 h at 110 C (in DMF).
In the latter case, strong tarring occurred. The solvent
and excess dihalide VIIIa were removed under re-
duced pressure, and the residue (a viscous oil) was
1
analyzed by H NMR spectroscopy. The residue ob-
tained from the reaction mixture in acetonitrile was
subjected to chromatography on silica gel in a glass
column, 1.5 m 5 cm, using hexane benzene (4:1) as
eluent. The first fraction (Rf 0.22) contained pure
compound IXa or Xa; yield 18 and 11%, respectively.
Diethyl 2-phenylimidazole-4,5-dicarboxylate
1
(VIa). mp 200 202 C. H NMR spectrum, , ppm:
1.31 t (6H, CH3), 4.29 q (4H, OCH2), 7.48 m (3H,
Harom), 8.08 d (2H, Harom), 13.70 (1H, NH). Mass
spectrum: m/z 288 [M]+ . Found, %: C 62.39; H 5.60.
C15H16N2O4. Calculated, %: C 62.49; H 5.59. Hydro-
Diethyl 1-(2-chloroethyl)-2-phenylimidazole-4,5-
1
dicarboxylate (IXa). mp 122 125 C. H NMR spec-
1
chloride: mp 120 125 C. H NMR spectrum, , ppm:
trum, , ppm: 1.31 t (6H, CH3), 3.78 t (2H, CH2),
4.29 q (4H, OCH2), 4.58 t (2H, CH2), 7.58 m (3H,
Harom), 7.66 d (2H, Harom). Mass spectrum: m/z 350
[M]+ . Found, %: C 58.07; H 5.57. C17H19ClN2O4.
Calculated, %: C 58.21; H 5.46.
1.30 t (6H, CH3), 4.28 q (4H, OCH2), 7.34 t (2H,
NH+2), 7.57 m (3H, Harom), 8.14 d (2H, Harom). Found,
%: C 55.28; H 5.36. C15H17ClN2O4. Calculated, %:
C 55.48; H 5.28.
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SYNTHESIS AND N-ALKYLATION OF 2-ALKYL-
953
Dimethyl 1-(2-chloroethyl)-2-phenylimidazole-
4,5-dicarboxylate (Xa). mp 134 137 C. 1H NMR
spectrum, , ppm: 3.72 s (6H, OCH3), 3.78 t (2H,
CH2), 4.58 t (2H, CH2), 7.59 m (3H, Harom), 7.67 d
(2H, Harom). Mass spectrum: m/z 322 [M]+ . Found,
%: C 55.65; H 4.68. C15H15ClN2O4. Calculated, %:
C 55.82; H 4.68.
and Hayashi, M., J. Med. Chem., 1981, vol. 24, no. 10,
p. 1139.
4. Snyder, H.R., Handrick, R.G., and Brooks, L.A., Or-
ganic Syntheses, Horning, E.C., Ed., New York: Wiley,
1955, collect. vol. 3, p. 471.
5. Shipper, E. and Day, A., Heterocyclic Compounds,
Elderfield, R.C., Ed., New York: Wiley, 1957, vol. 5.
Translated under the title Geterotsiklicheskie soedine-
niya, Moscow: Inostrannaya Literatura, 1961, vol. 5,
p. 172.
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