Synthesis of α-nitro derivatives of δ-oxocarboxylic and glutaric acids in heterogeneous catalytic system ionic liquid-KHCO3

Article abstract of DOI:10.1007/s11172-007-0230-x

An expedient method for the synthesis of α-nitro-δ- oxocarboxylic and α-nitroglutaric acid esters, including ones with isoprenoid substituents, by the solvent-free reaction of the corresponding alkyl α-nitrocarboxylates with activated olefins, assisted by

Full text of DOI:10.1007/s11172-007-0230-x

Russian Chemical Bulletin, International Edition, Vol. 56, No. 8, pp. 1487—1494, August, 2007
1487
Synthesis of αꢀnitro derivatives of δꢀoxocarboxylic and glutaric acids
in heterogeneous catalytic system ionic liquid—KHCO3
S. G. Zlotin,ꢀ G. V. Kryshtal, G. M. Zhdankina, A. V. Bogolyubov, S. G. Postikova, and V. A. Tartakovsky
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: zlotin@ioc.ac.ru
An expedient method for the synthesis of αꢀnitroꢀδꢀoxocarboxylic and αꢀnitroglutaric acid
esters, including ones with isoprenoid substituents, by the solventꢀfree reaction of the correꢀ
sponding alkyl αꢀnitrocarboxylates with activated olefins, assisted by heterogeneous catalytic
system KHCO3—1ꢀbutylꢀ3ꢀmethylimidazolium tetrafluoroborate ([bmim][BF4]), was elaboꢀ
rated. The product yields remain stable even after eight recycles of the catalytic system. The
synthesized dimethyl 2ꢀ(poly)prenylꢀ2ꢀnitropentanedioates upon treatment with Fe in AcOH
were reduced to 2ꢀ(poly)prenylꢀ5ꢀoxopyrrolidineꢀ2ꢀcarboxylates.
Key words: ionic liquids, the Michael reaction, nitro compounds, olefins, isoprenoids,
catalysis, reduction, pyrrolidinꢀ2ꢀones.
Addition of nitroalkanes to activated olefins (the
Michael reaction) is one of the most simple and conveꢀ
nient methods for the formation of a C—C bond.1
The reaction allows one in a single experimental step
from available precursors to obtain complex polyfunсꢀ
tional compounds, intermediate products for the synꢀ
thesis of natural and biologically active substances.2 Bases
are usually used as the catalysts. The preference is given
to the more convenient from the technological point
of view heterogeneous catalysts (Al2O3,3 Al2O3•KF,4
Amberlystꢀ21 5 etc.).
As a rule, the reaction is carried out in organic solꢀ
vents2 or in excess of nitroalkane.6 Ionic liquids (IL) (in
particular, [bmim][ОН]7 and [bmim][РF6],8 bmim is
1ꢀbutylꢀ3ꢀmethylimidazolium] are also used as the solꢀ
vents: due to the low vapor pressure and low solubility in
hydrocarbons, they are easy to recover. Reactions in IL
were carried out under homogeneous conditions.
Recently, we elaborated a convenient method for the
synthesis of γꢀnitroketones and γꢀnitrocarboxylic acid esꢀ
ters from nitroalkanes (nitroethane, 2ꢀnitropropane, and
nitrocyclohexane) and α,βꢀunsaturated carbonyl comꢀ
pounds with the assistance of simple and efficient heteroꢀ
geneous catalytic system K2CO3—IL depriving of the use
of organic solvents (see Ref. 9). The adducts were formed
in high yields with the use of minimum amount of IL
(90 mol.%). The system preserved its activity in three
reaction cycles.
In the present work, αꢀnitrocarboxylic esters 1 and
activated olefins 2 with the use of heterogeneous cataꢀ
lytic system, solid base—IL, were converted to αꢀnitro
derivatives of δꢀoxocarboxylic and glutaric acids 3, inꢀ
cluding intermediate products for the synthesis of analogs
of pharmacologically active substances (Scheme 1).
Methyl nitroacetate (1a), methyl 5ꢀmethylꢀ2ꢀnitrohexꢀ
4ꢀenoate (1b), and methyl 5,9ꢀdimethylꢀ2ꢀnitrodecaꢀ4,8ꢀ
dienoate (1c) were used as the starting αꢀnitrocarboxylates,
acrolein (2a), α,βꢀunsaturated ketones 2b—h, and esters
2i—k, as the activated olefins (see Scheme 1).
The earlier unknown αꢀnitrocarboxylic acid esters 1b,c
were synthesized by alkylation of methyl nitroacetate (1a)
with prenyl and geranyl bromides, respectively, in DMF
in the presence of benzyltriethylammonium chloride
([BTEA]Cl) as the phaseꢀtransfer catalyst. The yields of
alkylation products 1b,c were 53—65% (Scheme 2). Hoꢀ
molog of 1b, ethyl 5ꢀmethylꢀ2ꢀnitrohexꢀ4ꢀenoate, has
been synthesized earlier10 by the base assisted decarboxyꢀ
lation of diethyl 2ꢀprenylꢀ2ꢀnitromalonate, though the
yield of the product did not exceed 25—30%.
Isoprenoid diene 2h was synthesized by the reaction of
citronellal with phenacyltriphenylphosphonium bromide
in the presence of potassium carbonate in 62% yield
(Scheme 3).
Nitroacetic acid esters, being strong СНꢀacids, are
capable of reacting with activated olefins upon treatꢀ
ment with soft bases.11 In order to find the optimal compoꢀ
sition of the catalytic system, we investigated the reaction
of 1а with 1,3ꢀdiphenylpropꢀ2ꢀenꢀ1ꢀone (сhalcone 2b) in
the presence of neutral and acidic salts of carbonic acid
and various IL. Easily available 1ꢀbutylꢀ3ꢀmethylimidazoꢀ
lium ([bmim][BF4]) and 1ꢀbutylꢀ2,3ꢀdimethylimidazoꢀ
lium ([bdmim][BF4]) tetrafluoroborates and 1ꢀbutylꢀ3ꢀ
methylimidazolium hexаfluorophosphate ([bmim][РF6])
were used as the IL (Table 1). Both the base and IL were
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1431—1438, August, 2007.
1066ꢀ5285/07/5608ꢀ1487 © 2007 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 56, No. 8, August, 2007
Zlotin et al.
Scheme 1
Scheme 3
i. K2CO3, dioxane, 100 °C.
In contrast to nitroalkanes without electronꢀwithdrawꢀ
ing substituent in αꢀposition to the nitro group (for EtNO2
pKa = 8.6),12b nitro ester 1а (pKa = 5.8)12a,b formed the
Michael adduct 3b in high yield upon treatment with
metal bicarbonates (see Table 1, entries 5—7). However,
the yield of 3b was significantly lower on catalysis with
more basic carbonates (see Table 1, entries 1—3). Apparꢀ
ently in contrast to carbonates (pKa = 10.25 for conjugate
acid HCO3–),12c bicarbonates (pKa = 6.37 for conjuꢀ
gate acid H2CO3)12c are able to selectively deprotonate
СНꢀacid 1а in the presence of product 3b, shifting the
equilibrium toward the latter. This suggestion was conꢀ
firmed by the increase in the yield of 3b, when amount of
the base was decreased (see Table 1, entries 2—4). The
reaction proceeded faster in IL containing [BF4]– anion
R1 = H (1a, 3a—k), Me2C=CHCH2 (1b, 3m,n),
H[CH2C(Me)=CHCH2]2 (1c, 3o,p)
Compounds
R2
R3
R4
R5
2a, 3a*,m,o
2b, 3b
2c, 3c
2d, 3d
2e, 3e
2f, 3f
2g, 3g
2h, 3h
2i, 3i,n,p
2j, 3j
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Ph
Ph
Me
Ph
Me
Ph
**
**
H
Me
**
Me
Me
Me
cꢀPr
Me
Ph
OMe
OMe
OEt
Table 1. Optimization of the reaction conditions between 1а
and 2ba
H
H
2k, 3k
CO2Et
Entry
Base
(mol.%)
IL
(mol.%)
T/°C τ/hb Yield
* Due to resinification during the reaction 1a + 2a, product 3a could
not be obtained. ** Me2C=CH(CH2)2CH(Me)CH2.
of 3b
(%)
i. MHCO3 (30 mol.%), [bmim][BF4] (30 mol.%), 20—40 °C.
1
2
3
4
5
6
7
8
9
Na2CO3 (30)
K2CO3 (200)
K2CO3 (30)
K2CO3 (15)
NaHCO3 (30) [bmim][BF4] (90)
KHCO3 (200) [bmim][BF4] (400) 20
KHCO3 (30)
KHCO3 (30)
KHCO3 (30)
[bmim][BF4] (90)
[bmim][BF4] (400) 20
[bmim][BF4] (90)
[bmim][BF4] (90)
20
60
8
8
48
12
2
37
32
63
94
92
95
92
92
87
98
98
99
0
Scheme 2
20
20
20
[bmim][BF4] (90)
[bdmim][BF4] (90) 20
20
8
10
20
14
6
6
70
[bmim][PF6] (90)
[bmim][BF4] (30)
[bmim][BF4] (30)
[bmim][BF4] (30)
—
20
20
40
40
20
10 KHCO3 (30)
11 KHCO3 (30)
12c KHCO3 (30)
13 KHCO3 (30)
n = 1 (1b), 2 (1c)
Conditions: K2CO3, [BTEA]Cl (cat), DMF.
a Reagents loading: 1а (100 mol.%), 2b (100 mol.%).
b The reactions were conducted until 1а disappeared (TLC moniꢀ
toring), excluding entry 13.
used in amounts of 30—400 mol.%. The reactions were
carried out until the disappearance of the СНꢀform of
nitro compound 1а from the mixture (TLC monitoring).
c The reaction was conducted under sonication

αꢀNitroꢀδꢀoxocarboxylic esters
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 8, August, 2007
1489
than in IL with [PF6]– anion (see Table 1, entries 7—9).
When amount of IL was reduced to 30 mol.%, the yield of
3b remained high (see Table 1, entries 10 and 11). Ultraꢀ
sound may be applied instead of mechanical stirring of
the reaction mixture (see Table 1, entry 12). Further deꢀ
crease of IL amount (to 10—15 mol.%) led to a decrease
in the yield of 3b. No reaction took place in the absence
of IL (see Table 1, entry 13).
The KHCO3—[bmim][BF4] catalytic system
(30 mol.% each), which in the model reaction proꢀ
vided the highest yield of product 3b with the minimum
amount of catalyst, was applied to the synthesis of esters
of αꢀnitroꢀδꢀoxocarboxylic 3b—h,l,m,o and αꢀnitroꢀ
glutaric 3i—k,n,p acids, containing substituents of various
structure (Table 2).
Acrolein (2а) and methyl acrylate (2i) devoid of subꢀ
stituents at βꢀcarbon atom were found to be the most
reactive. Olefins 2g,h,l with isoprenoid substituents and
mesityl oxide (2e) with two methyl groups in βꢀposition
were the least reactive. Nevertheless, when the reaction
was carried to complete conversion of the olefin, we were
able to obtain the earlier unknown nitro compounds of
isoprenoid series 3g,h,k—p (Schemes 4 and 5), as well as
products 3b—d, the yields of which exceeded those found
in the literature even with the shorter reaction time (see
Table 2, entries 1—3).
In a number of cases, the reactions lead to the formaꢀ
tion of diastereomeric mixtures of 3 in ratios (1 : 1)—(2 : 1)
(1Н NMR data). For compounds 3k and 3l with four
1
chiral centers, the ratio of the detected by Н NMR
Table 2. Yields and physical and chemical properties of adducts 3a
Entry Reaꢀ
gents
τ/h
Proꢀ Yield 3 (%)
duct (cycle)
M.p./°С
or nD
1H NMR spectrum (CDCl3)
20
δ, (J/Hz)b
1
1a + 2b
6
[48
(20 °С)]13
3b 98 (1), 99 (2),
99 (3), 99 (4),
89 (5), 99 (6)c,
99 (7), 99 (8)
[40]13 dr 2 : 1
3c 76 [44]14
dr 1 : 1
114—115
3.50—3.70 (m, 2 Н, CH2C=O); 3.60 (s, 1 H, OMe);
[114—116]10 3.77 (s, 2 H, OMe); 4.50 (m, 1 H, CHPh); 5.55 (d,
0.34 Н, CHNO2, J = 8.5); 5.60 (d, 0.66 Н, CHNO2,
J = 9.5); 7.25 (m, 5 Н, Ph); 7.40 (m, 2 Н, Ph);
7.50 (m, 1 Н, Ph); 7.90 (d, 2 Н, Ph, J = 7.5)
2
3
1a + 2c
8d
1.4490
1.07 (d, 3 H, Me, J = 7.0); 2.13 (s, 3 H, MeCO); 2.45—2.75 (m,
2 Н, CH2); 3.0 (m, 1 Н, СН); 3.80 (s, 3 H, OMe); 5.20 (d,
0.5 Н, CHNO2, J = 5.5); 5.27 (d, 0.5 Н, CHNO2, J = 6.3)
2.05 (s, 3 H, MeC=O); 2.95—3.15 (m, 2 Н, CH2); 3.60 (s, 1 H,
OMe); 3.80 (s, 2 H, OMe); 4.25 (m, 1 H, CHPh); 5.45 (d,
0.34 Н, CHNO2, J = 8.2); 5.50 (d, 0.66 Н, CHNO2, J = 9.0);
7.20—7.40 (m, 5 Н, Ph)
1.20, 1.23 (both s, 3 H each, Me); 2.10 (s, 3 H, MeC=O);
2.67, 2.82 (both d, 1 H each, CH2, J = 17.7);
3.75 (s, 3 H, OMe); 5.85 (s, 1 Н, CHNO2)
0.75—0.95 (m, 4 Н, 2 CH2 of cyclоpropane); 1.85 (m, 1 Н, CH,
of cyclоpropane); 2.95—3.20 (m, 2 Н, CH2C=O); 3.60 (s, 1 H,
OMe); 3.80 (s, 2 H, OMe); 4.27 (m, 1 H, CHPh); 5.45 (d,
0.34 Н, CHNO2, J = 8.0); 5.52 (d, 0.66 Н, CHNO2, J = 9.0);
7.20—7.35 (m, 5 Н, Ph)
0.85—0.95 (m, 3 Н, C(12)H3); 1.10—1.45 (m, 5 Н, C(4)Н2,
C(5)H, C(6)H2); 1.57, 1.65 (both s, 3 H each, C(10)H3,
C(11)H3); 1.90 (m, 2 Н, C(7)H2); 2.15 (s, 3 H, MeC=O);
2.50—3.05 (m, 3 Н, СН2, C(3)H); 3.80 (s, 3 H, OMe); 5.05
(m, 1 H, C(8)H); 5.35 (m, 1 Н, C(2)H)
0.85—1.00 (m, 3 Н, C(12)H3); 1.20—1.55 (m, 5 Н, C(4)Н2,
C(5)H, C(6)H2); 1.57, 1.65 (both s, 3 H each, C(10)H3,
C(11)H3); 1.95 (m, 2 Н, C(7)H2); 3.05—3.40 (m, 3 Н, CН2,
C(3)H); 3.80 (s, 3 H, OMe); 5.05 (m, 1 H, C(8)H); 5.48 (d,
0.66 Н, C(2)H, J = 6.0); 5.53 (d, 0.34 Н, C(2)H, J = 7.0);
7.47 (t, 2 Н, Ph, J = 7.0); 7.58 (t, 1 Н, Ph, J = 7.0);
7.95 (m, 2 H, Ph)
[140
(100 °С)]14
1a + 2d 14, 6d
[110
3d 90 (1), 87 (2),
85 (3) [84e]15
dr 2 : 1
102—103
(20 °С)e]15
4
1a + 2e
1a + 2f
22d
[70
(70 °С)]16
16d
3e 55 [83]16
1.4500
[1.4507]16
5
3f
95
70—71
1.4695
1.5135
dr 2 : 1
6
7
1a + 2g
1a + 2h
40d
40d
3g 75
3h 73
dr 2 : 1
8
1a + 2i
10 f
[26
(65 °С)]17
3i
90 [75]17
dr 1 : 1
1.4460
[1.4468]18
2.40, 2.55 (both m, 2 H each, 2 СН2); 3.65, 3.80 (both s,
3 H each, 2 OMe); 5.30 (t, 1 H, CHNO2, J = 7.0)
(to be continued)

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Zlotin et al.
Table 2 (continued)
Entry Reaꢀ
gents
τ/h
Proꢀ Yield 3 (%)
M.p./°С
or nD
1H NMR spectrum (CDCl3)
20
duct
(cycle)
δ, (J/Hz)b
9
1a + 2j
12d
20d
3j
69
dr 1 : 1
1.4470
1.12 (d, 3 Н, CH3C, J = 7.0); 2.42 (ddd, 1 H, CH2, 1J = 17.2,
2J = 7.8, 3J = 2.0); 2.57 (dd, 1 H, CH2, 1J = 17.2, 2J = 5.5);
2.97 (m, 1 H, CH), 3.67 (s, 1.5 H, OMe); 3.80 (s, 1.5 H, OMe);
5.25 (d, 0.5 Н, CHNO2, J = 6.5); 5.30 (d, 0.5 Н, CHNO2,
J = 6.5)
0.92 (m, 3 Н, Me); 1.10—1.45 (m, 5 Н, 2 СН2, СH); 1.30 (t,
6 Н, 2 Ме, J = 7.0); 1.60, 1.68 (both s, 3 H each, 2 Mе); 1.97
(m, 2 Н, СH2); 3.23, 3.68 (both m, 1 H each, C(2)H, C(3)H);
3.82 (s, 3 H, OMe); 4.20 (q, 4 Н, 2 CH2O, J = 7.0); 5.08
(t, 1 H, =СH, J = 7.0); 5.55, 5.59, 5.63, 5.68 (all d,
0.25 H each, C(1)H, J = 6.0)
1.05—1.25 (m, 3 Н, MeC(2)); 1.70 (s, 3 Н, MeC=);
1.85—2.80 (m, 7 Н, C(4)H2, C(6)H2, C(1)Н, C(2)Н, C(5)Н);
3.85 (m, 3 H, OMe); 4.65—4.85 (m, 2 H, CH2=); 5.20 (d,
0.2 Н, CHNO2, J = 6.0); 5.27 (d, 0.2 Н, CHNO2, J = 2.0);
5.36 (d, 0.3 Н, CHNO2, J = 6.0); 5.45 (d, 0.3 Н, CHNO2,
J = 2.0)
10 1a + 2k
3k 63
dr 1 : 1 :
1.4625
: 1 : 1
11
1a + 2l
15d
3l
73
dr 3 : 2 :
: 3 : 2
1.4880
12 1b + 2a
4 f
6 f
6 f
3m 86 (1), 86 (2)
3n 88 (1), 88 (2)
3o 73
1.4780
1.4642
1.4900
1.60, 1.68 (both s, 3 H each, C(5)Me2); 2.42, 2.52 (both m,
1
2 H each, 2 СH2); 2.85 (dd, 1 H, C(3)H2, J = 18.5, 2J = 7.5);
2.95 (dd, 1 H, C(3)H2, 1J = 18.5, 2J = 7.5); 3.75 (s, 3 H, OMe);
4.90 (t, 1 Н, C(4)Н, J = 7.5); 9.70 (s, 1 Н, СH=О)
13
1b + 2i
1.60, 1.68 (both s, 3 H each, 2 Mе); 2.33, 2.47 (both m,
2 H each, C(3)H2, C(4)H2); 2.83 (dd, 1 H, СH2, 1J = 17.5,
2J = 8.0); 2.93 (dd, 1 H, СH2, 1J = 17.5, 2J = 8.0); 3.63, 3.75
(both s, 3 H each, 2 OMe); 4.89 (t, 1 Н, =СН, J = 8.0)
1.58, 1.62, 1.68 (all s, 3 H each, 3 Me); 2.00 (br.s, 4 Н, C(6)H2,
C(7)H2); 2.50, 2.58 (both m, 2 H each, 2 СH2); 2.90 (dd, 1 H,
C(3)H2, 1J = 16.5, 2J = 8.0); 2.98 (dd, 1 H, C(3)H2, 1J = 16.5,
2J = 8.0); 3.80 (s, 3 H, OMe); 4.92 (t, 1 Н, C(4)Н, J = 8.0);
5.03 (t, 1 Н, C(8)Н, J = 7.5); 9.73 (s, 1 Н, СH=О)
14 1c + 2a
15
1c + 2i
10 f
3p 82 (1), 82 (2)
1.4765
1.58, 1.62, 1.68 (all s, 3 H each, 3 Me); 2.02 (br.s, 4 Н, 2 СH2);
2.38, 2.50 (both m, 2 H each, C(3)H2, C(4)H2); 2.89 (dd, 1 H,
1
СH2, 1J = 16.5, 2J = 8.0); 2.97 (dd, 1 H, СH2, J = 16.5,
2J = 8.0); 3.67, 3.78 (both s, 3 H each, 2 OMe); 4.92 (t, 1 Н,
=СН, J = 8.0); 5.03 (t, 1 Н, =СН, J = 7.5)
a Reaction conditions: 1a—c (100 mol.%), 2a—l (100 mol.%), КНCO3 (30 mol.%), [bmim][BF4] (30 mol.%), 40 °С. The literature
data are given in brackets.
b In the IR spectra of compounds 3b—p, characteristic signals for nitro and carbonyl groups 1352—1372 (NO2 symm.), 1556—1564
(NO2 asymm.), 1716—1760 cm–1 (C=О) are presented.
c КНСО3 was added (0.30 g, 3 mmol).
d The reactions were caried out in an ultrasonic tank without mechanical stirring.
e Data for the reaction of 2d with ethyl nitroacetate.
f The reactions were caried out at 20 °С.
spectroscopy diastereomers are 3 : 2 : 3 : 2 and 1 : 1 : 1 : 1,
respectively (see Table 2, entries 10 and 11).
of the catalyst, in which the deprotonation of nitro comꢀ
pound 1 and the interaction of nitronate anion with olefin
2 take place. Reaction product 3, as soon as it forms, is
being removed from the zone of contact with the catalyst
into organic phase, which increases the selectively of the
process. For the reaction to be efficient, it is expedient to
use the finely powdered КНСО3. Apparently, ultrasound
increases the degree of dispersion of the solid base, resultꢀ
ing in the intensification of the transfer of reagents and
product between phases.
The reaction under consideration proceeds in heteroꢀ
geneous system, consisting of the solid (КНСО3) and two
liquid (IL and eutectic solution of compounds 1—3)
phases (Fig. 1). Apparently, IL in this system simultaꢀ
neously plays the role of the solvent, decreasing the visꢀ
cosity of the reaction mixture, and of the phaseꢀtransfer
catalyst (PTC). Probably, the poorly soluble in the reacꢀ
tants IL forms the soꢀcalled omegaꢀphase19 on the surface

αꢀNitroꢀδꢀoxocarboxylic esters
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 8, August, 2007
1491
Scheme 4
deprotonation of 1ꢀbutylꢀ3ꢀmethylimidazolium cation to
the corresponding carbene and its further transformaꢀ
tions22 under the reaction conditions take place.
The KHCO3—[bmim][BF4] catalytic system (see
Fig. 1, the region bounded by a double line) is easily
regenerated. After the removal of organic phase, fresh
portions of reagents 1 and 2 were added to the residue and
the process was carried out anew (see Table 2, entries 1, 3,
12, 13, and 15). The system retained its activity at least
in eight reaction cycles. Though after the fifth cycle, a
small amount of the base (30 mol.%) was required to be
added to make up for the loss by its gradual conversion
to Н2СО3.
The obtained αꢀnitro derivatives of δꢀoxocarboxylic
and glutaric acids 3g,h,k—p containing isoprenoid subꢀ
stituents are of interest as intermediate products in the
synthesis of isoprenoid amino acid analogs of the woundꢀ
healing medicine "metaprogerol".23 On the model comꢀ
pounds 3n,p, it was shown that the nitro group in the
compounds obtained can be selectively reduced to amino
groups upon treatment with Fe powder in AcOH with the
С=С bond remaining intact (see also Ref. 24). Under the
reaction conditions, the formed amino derivatives unꢀ
dergo cyclization to the corresponding 2ꢀ(poly)prenylꢀ5ꢀ
oxopyrrolidineꢀ2ꢀcarboxylates 4a,b (Scheme 6).
i. KHCO3 (30 mol.%), [bmim][BF4] (30 mol.%), 40 °C, ultraꢀ
sound.
Scheme 5
Scheme 6
i. KHCO3 (30 mol.%), [bmim][BF4] (30 mol.%), 20 °C.
The KHCO3—[bmim][BF4] system is more chemiꢀ
cally stable than the earlier proposed base—IL heterogeꢀ
neous systems, containing the highly basic hydroxides19с,20
or metal carbonates.9,21 In contrast to the latter, no side
i. Fe, AcOH, reflux, 4 h.
In conclusion, we elaborated an efficient and meeting
with the "green chemistry" requirements25 method for the
synthesis of αꢀnitro derivatives of glutaric and δꢀoxoꢀ
carboxylic acids by the reaction of nitroacetic ester deꢀ
rivatives with the electronꢀdeficient olefins in heteroꢀ
geneous catalytic system KHCO3—[bmim][BF4]. By this
method, we were able to obtain the earlier unknown nitro
derivatives of isoprenoids 3g,h,k—p, including intermeꢀ
diate products for the synthesis of pharmacologically acꢀ
tive isoprenoid amino acids.26 Apparently, the regeneratꢀ
able heterogeneous catalytic system KHCO3—IL can be
successfully used for the other baseꢀpromoted reactions
of strong СНꢀacids with electrophiles.
Organic phase
An
Cat
Cat
An
KHCO3
Cat
An
An
Cat
ωꢀPhase
Reactants
Product
Fig. 1. Schematic representation of the catalytic system action.
Cat = bmim, An = BF4

1492
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 8, August, 2007
Zlotin et al.
K2CO3 (2.10 g, 15 mmol) and phenacyltriphenylphosphonium
bromide (4.60 g, 10 mmol) in dioxane (15 mL). The reaction
mixture was vigorously stirred for 6 h at 100 °С and cooled to
~20 °С, the precipitate was filtered off, the filtrate was concenꢀ
trated under reduced pressure (40 °С, 40 Torr), the residue was
distilled in vacuo to afford 2h (1.60 g, 62%), b.p. 130—135 °С
(0.7 Torr), nD20 1.5305. Found (%): С, 84.59; H, 9.26. C18H24O.
Experimental
NMR spectra were recorded on a Bruker AMꢀ300
(300.13 MHz (1H)) and Bruker WMꢀ250 (250.13 MHz (1H) and
69.9 MHz (13С)) spectrometers in CDCl3. Chemical shifts for 1H
were determined from the internal standard, SiMe4, for 13С,
from CDCl3. IR spectra were recorded on a Specord Mꢀ82
instrument in KBr pellets or for the neat samples. Elemental
analysis was performed on a Perkin—Elmer 2400 microanalyser.
In ultrasound experiments, a 1.6ꢀL RELTEK 1/100 TH ultraꢀ
sonic tank with operating frequency 47 kHz was used. The
сonversion of reagents and the products purity were monitored
by TLC on Silufol plates with 5% EtOAc in benzene as the
eluent, the visualization was done by the UVꢀlight and I2 vapors.
Purification of the synthesized compounds, if not stated otherꢀ
wise, was performed by column chromatography on Acros silica
gel (1.060—0.200 µm).
1
Calculated (%): C, 84.32; H, 9.44. Н NMR, δ: 0.97 (m, 3 Н,
C(12)H3); 1.20—1.45 (m, 2 Н, C(6)Н2); 1.60, 1.67 (both s,
3 Н each, C(10)H3, C(11)H3); 1.90—2.35 (m, 5 Н, C(4)Н2,
C(5)Н, C(7)Н2); 5.10 (t, 1 Н, C(8)Н, J = 7.5 Hz); 6.85 (d, 1 Н,
C(2)Н, J = 16.0 Hz); 7.05 (m, 1 Н, C(3)Н); 7.40—7.50 (m, 3 Н,
Ph); 7.90 (d, 2 Н, Ph, J = 7.0 Hz). 13C NMR, δ: 17.7 (C(10));
19.6 (C(12)); 25.6, 25.8 (C(7), C(11)); 32.7 (C(5)); 36.8 (C(6));
40.3 (C(4)); 124.5 (C(8)); 127.2 (C(2)); 128.0, 128.4, 132.6
(all CH of phenyl); 131.5 (C(9)); 138.1 (C of phenyl); 148.8
(C(3)); 190.7 (C(1)).
Starting compounds 1a and 2a,b,d,e,i,j,l, citronellal, phenꢀ
acyltriphenylphosphonium bromide, 1ꢀmethylimidazole, 1,2ꢀdiꢀ
methylimidazole, K2CO3, Na2CO3, KHCO3, and NaHCO3 were
purchased from Acros, prenyl bromide and geranyl bromide,
from Aldrich and were used in the reactions without additional
Reaction of nitro compounds 1 with activated olefins 2 (genꢀ
eral procedure). A mixture of the powdered in a porcelain mortar
KHCO3 (0.30 g, 3 mmol), [bmim][BF4] (0.70 g, 3 mmol), nitro
compound 1 (10 mmol), and olefin 2 (10 mmol) was vigorously
stirred with a magnetic stirrer or kept in ultrasonic tank for
4—40 h at 20—40 °С (Table 2) until the starting compounds
disappeared (TLC monitoring). The reaction mixture was seꢀ
quentially extracted with Et2O (2×5 mL) and benzene (2×5 mL).
The combined organic extract was washed with water (3×25 mL),
dried with MgSO4, and the solvent was evaporated at reduced
pressure (40 °С, 40 Torr). The crude product was purified on
a column with SiO2, sequentially eluenting with nꢀhexane,
nꢀhexane—benzene mixture (1 : 1), and benzene. The yields,
29
purification. Activated olefins 2c,27 2f,16c 2g,28 and 2k
and ionic liquids [bmim][BF4],30 [bmim][PF6],31 and
[bdmim][BF4]32 were synthesized by the known procedures.
Methyl 5ꢀmethylꢀ2ꢀnitrohexꢀ4ꢀenoate (1b). A solution of
1ꢀbromoꢀ3ꢀmethylbutꢀ2ꢀene (1.49 g, 10 mmol) in DMF (2 mL)
was added dropwise with stirring to a cooled to –10 °С suspenꢀ
sion of K2CO3 (1.66 g, 12 mmol), [BTEA]Cl (0.10 g, 0.5 mmol),
and methyl nitroacetate (1.19 g, 10 mmol) in the same solvent
(3 mL). The reaction mixture was vigorously stirred for 0.5 h at
–10 °С, then for 2 h at 20 °С (TLC monitoring), cooled with
iceꢀcold water to +5 °С, carefully acidified with 1 N HCl
to рН ~2. The obtained solution was extracted with Et2O
(3×10 mL), the combined organic extract was sequentially
washed with brine (2×20 mL) and water (20 mL) and dried with
MgSO4. The filtrate was concentrated at reduced pressure (40 °С,
40 Torr), the residue was distilled in vacuo to obtain 1b (1.22 g,
1
physical and chemical properties, and Н NMR spectroscopic
data of compounds 3 are given in Table 2. Elemental analysis
data and 13С NMR spectroscopic data of the newly synthesized
products 3f—h,j—p are given below.
Methyl 5ꢀcyclopropylꢀ2ꢀnitroꢀ5ꢀoxoꢀ3ꢀphenylpentanoate
(3f). Colorless crystals, m.p. 70—71 °С (nꢀhexane). Found (%):
C, 62.07; H, 6.04; N, 4.65. C15H17NO5. Calculated (%):
C, 61.85; H, 5.88; N, 4.81. 13C NMR, δ: 10.4, 10.5, 10.7, 10.8,
16.8, 17.5 (all C of cyclopropyl); 44.6, 47.7 (both C(3)); 45.9,
46.0 (both OМе); 86.3, 87.0 (both C(2)); 127.4, 127.6, 128.0,
128.2, 128.5, 128.8, 128.9 (all C of phenyl); 138.2 (C(1)); 206.9,
207.6 (both C(5)).
Methyl 5,9ꢀdimethylꢀ2ꢀnitroꢀ3ꢀ(2ꢀoxopropyl)decꢀ8ꢀenoate
(3g). Colorless viscous oil. Found (%): C, 61.17; H, 8.71; N, 4.61.
C16H27NO5. Calculated (%): C, 61.32; H, 8.68; N, 4.47.
13C NMR, δ: 17.6, 18.8, 19.2, 19.3, 19.9 (all Me); 25.0, 25.1,
25.2, 25.6 (all C(7)); 29.5, 29.6, 29.7, 29.8, 30.1 (all C(5)); 32.6,
32.7, 32.8 (all MeC=O); 35.9, 36.6, 36.8, 37.1, 37.4, 37.8, 38.1
(all C(3), C(4), C(6)); 43.0, 43.3, 43.6, 43.9 (all CH2C=O);
53.2, 53.3 (both OМе); 89.0, 89.4, 89.5, 90.0 (all C(2)); 124.2,
124.3 (both C(8)); 131.4, 131.5 (both C(9)); 164.3, 164.4, 164.6,
164.7 (all C(1)); 205.8, 206.0, 206.1, 206.3 (all C=O).
20
65%), b.p. 120—125 °С (10 Torr), nD 1.4530. Found (%):
C, 51.58; H, 6.84; N, 7.30. C8H13NO4. Calculated (%): C, 51.33;
1
H, 7.00; N, 7.48. Н NMR, δ: 1.62, 1.70 (both s, 3 Н each,
2 Ме); 2.80, 2.95 (both m, 1 Н each, СН2); 3.80 (s, 3 Н, ОМе);
4.95—5.50 (m, 2 Н, =СН, CHNO2). 13C NMR, δ: 17.8 (Me);
23.7 (Me); 24.2 (C(3)); 53.4 (ОMe); 87.7 (C(2)); 115.8 (C(4));
138.1 (C(5)); 164.8 (C(1)).
Methyl 5,9ꢀdimethylꢀ2ꢀnitrodecaꢀ4,8ꢀdienoate (1с). The
product was synthesized similarly to 1b from methyl nitroacetate
(1.19 g, 10 mmol), geranyl bromide (2.17 g, 10 mmol), K2CO3
(1.66 g, 12 mmol), and [BTEA]Cl (0.10 g, 0.5 mmol). The
initial reaction temperature, 0 °С, the stirring time at 20 °С, 7 h.
Product 1с (1.35 g, 53%) was obtained, b.p. 135—142 °С
(0.5 Torr), nD20 1.4757. Found (%): C, 61.41; H, 8.49; N, 5.34.
C
13H21NO4. Calculated (%): C, 61.16; H, 8.29; N, 5.49.
Methyl 5,9ꢀdimethylꢀ2ꢀnitroꢀ3ꢀ(2ꢀoxoꢀ2ꢀphenylethyl)decꢀ8ꢀ
enoate (3h). Colorless viscous oil. Found (%): C, 66.89; H, 7.60;
N, 3.88. C21H29NO5. Calculated (%): C, 67.18; H, 7.79;
N, 3.73. 13C NMR, δ: 17.7 (C(10)); 19.1, 19.5, 20.0 (all C(12));
25.2, 25.3, 25.4, 25.7 (all C(7), C(11)); 29.8, 30.0, 30.1,
30.4 (all C(5)); 33.0, 33.1, 33.2, 33.3 (all C(3)); 36.1, 37.0,
37.5, 38.0, 38.1, 38.3, 38.4, 38.7, 38.9, 39.3 (all C(4), C(6),
CH2C=O); 53.3, 53.4, 53.5 (all OМе); 89.3, 89.8, 90.3
(all C(2)); 124.3, 124.4 (both C(8)); 128.0, 128.8, 133.5, 136.7
1Н NMR, δ: 1.55—1.75 (m, 9 Н, 3 MeС=); 1.97—2.12 (m, 4 Н,
СН2СН2); 2.85, 3.02 (both m, 1 Н each, СН2СHNO2); 3.81 (s,
3 Н, ОMe); 5.00—5.12 (m, 3 Н, 2 =СH; СНNO2). 13C NMR,
δ: 16.1 (C(5)Me); 17.6, 25.6 (both C(9)Me); 26.4 (C(7)); 29.1
(C(3)); 39.6 (C(6)); 53.4 (ОМе); 87.7 (C(2)); 115.7 (C(4));
123.6 (C(8)); 131.8 (C(9)); 141.7 (C(5)); 164.8 (C(1)).
(2E)ꢀ5,9ꢀDimethylꢀ1ꢀphenyldecaꢀ2,8ꢀdienꢀ1ꢀone (2h). Citꢀ
ronellal (1.54 g, 10 mmol) was added to a stirred suspension of

αꢀNitroꢀδꢀoxocarboxylic esters
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 8, August, 2007
1493
(all C of phenyl); 131.6 (C(9)); 163.1, 164.8 (both C(1));
197.3 (C=O).
tion was repeated eight times, CHCl3 (10 mL) was added to the
recovered catalytic system, precipitate of KHCO3 was filtered
off, the filtrate was concentrated on a rotary evaporator, the oily
residue was kept 3 h at 50 °С (10 Torr) to recover 0.51 g (78%)
of IL, which according to the 1Н NMR data was identical to the
freshly prepared sample of [bmim][BF4] (see Ref. 30).
Dimethyl 3ꢀmethylꢀ2ꢀnitropentanedioate (3j). Colorless oil.
Found (%): C, 44.03; H, 6.11; N, 6.26. C8H13NO6. Calcuꢀ
lated (%): C, 43.84; H, 5.98; N, 6.39. 13C NMR, δ: 15.8, 15.9
(both C(3)Me); 31.4 (C(3)); 36.5, 36.6 (both C(4)); 51.8, 53.3
(both OМе); 90.6 (C(2)); 164.0, 171.5 (both С=О).
Methyl 3ꢀbis(ethoxycarbonyl)methylꢀ5,9ꢀdimethylꢀ2ꢀnitroꢀ
decꢀ8ꢀenoate (3k). Colorless oil. Found (%): C, 58.05; H, 7.93;
N, 3.21. C20H33NO8. Calculated (%): C, 57.82; H, 8.01; N, 3.37.
13C NMR, δ: 13.9 (MeCH2); 17.6 (MeCH); 18.8; 19.0, 19.2,
19.5 (all MeC=); 25.2, 25.3, 25.5, 25.6 (all CH2CH=); 30.0,
30.2, 30.4, 30.6 (all MeCH); 35.7, 36.0, 36.1, 36.4, 36.7, 36.8,
37.0, 37.3 (all CH2CH); 52.1, 52.5 (C(2), C(3)); 53.2, 53.4
(OMe); 62.0 (MeCH2O); 88.3, 88.5, 88.7, 89.1 (all C(1));
124.3 (=CH); 131.5 (Me2C=); 163.0, 164.4; 167.7, 167.8, 167.9,
168.0 (all CO2).
Methyl 2ꢀ[2ꢀmethylꢀ3ꢀoxoꢀ5ꢀ(propꢀ1ꢀenꢀ2ꢀyl)cyclоhexyl]ꢀ2ꢀ
nitroacetate (3l). Colorless oil. Found (%): C, 58.23; H, 7.28;
N, 5.06. C13H19NO5. Calculated (%): C, 57.98; H, 7.11; N, 5.20.
13C NMR, δ: 11.3, 11.4, 12.4, 12.9 (all C(2)Me); 21.1, 21.2,
21.4, 21.5 (all MeC=); 27.8, 28.1, 31.3, 31.9 (all C(6)); 39.6,
39.8, 40.0, 40.4 (all C(5)); 43.3, 43.5, 43.7, 44.0, 44.8, 45.0,
45.3, 45.6, 45.7, 45.9, 46.2, 46.3 (all C(1), C(2), C(4)); 53.3,
53.5, 53.6, 53.7 (all OМе); 88.2, 88.3, 88.4, 88.7 (all C(2));
110.5, 110.6, 112.6, 112.8 (all CH2=C); 145.6, 146.2
(both C=CH2); 163.6, 163.9, 164.0, 164.1 (all CO2); 208.4,
209.3 (both C(3)).
Methyl 5ꢀmethylꢀ2ꢀnitroꢀ(3ꢀoxopropyl)hexꢀ4ꢀenoate (3m).
Colorless oil. Found (%): C, 54.50; H, 6.92; N, 5.59.
C11H17NO5. Calculated (%): C, 54.31; H, 7.04; N, 5.76.
13C NMR, δ: 18.0 (C(6)); 26.0 (C(5)Me); 26.2 (C(3)); 34.0,
38.5 (both CH2); 53.4 (OMe); 94.8 (C(2)); 114.4 (C(4)); 138.9
(C(5)); 166.9 (C(1)); 199.1 (C=O).
Methyl 2ꢀ(3ꢀmethylbutꢀ2ꢀenyl)ꢀ5ꢀoxopyrrolidineꢀ2ꢀcarbꢀ
oxylate (4а). A mixture of nitro compound 3n (0.20 g,
0.73 mmol), Fe powder (0.41 g, 7.3 mmol), and glacial AcOH
(2 mL) was refluxed for 4 h (until 3n disappeared, TLC monitorꢀ
ing). The reaction mixture was cooled to 20 °С, the excess of
AcOH was removed on a rotary evaporator (40 °С, 15 Torr).
Ethyl acetate (15 mL) was added to the residue, the inorganic
precipitate was filtered off and washed on the filter with EtOAc
(2×5 mL). The combined filtrate was concentrated on a rotary
evaporator, the residue was chromatographed on a column with
silica gel, sequentially eluting with Et2O—light petroleum (1 : 5)
and EtOAc—light petroleum (from 1 : 5 to 1 : 1) to obtain 0.11 g
20
(73%) of 4а. Yellow oil, nD 1.4838. Found (%): C, 62.73;
H, 8.26; N, 6.49. C11H17NO3. Calculated (%): C, 62.54; H, 8.11;
N, 6.63. IR, ν/cm–1: 1700 (C=O), 1740 (C=O), 3432 (NH).
1Н NMR, δ: 1.61, 1.71 (both s, 3 Н each, Me2C=); 2.02—2.20
(m, 1 Н, =CHСHH); 2.30—2.65 (m, 5 Н, 2 СH2, =CHСHH);
3.75 (s, 3 H, OMe); 5.02 (t, 1 Н, =СН, J = 7.3 Hz); 6.08 (br.s,
1 Н, NH). 13C NMR, δ: 17.9, 25.9 (Me2C=, CH2CH=); 29.9
(CH2C=O); 37.4 (CH2); 52.5 (OMe); 66.0 (CCO2Me); 116.6
(=CH); 137.1 (=CMe2); 174.0, 177.2 (both C=O).
Methyl 2ꢀ((E)ꢀ3,7ꢀdimethyloctaꢀ2,6ꢀdienyl)ꢀ5ꢀoxopyrrolꢀ
idineꢀ2ꢀcarboxylate (4b). The product was obtained similarly
to 4а from nitro compound 3p (0.20 g, 0.58 mmol), Fe powder
(0.33 g, 5.8 mmol), and glacial AcOH (2 mL) to isolate 0.13 g
20
(78%) of 4b. Yellow oil, nD 1.4872. Found (%): C, 69.01;
H, 9.14; N, 4.88. C16H25NO3. Calculated (%): C, 68.79; H, 9.02;
N, 5.01. IR, ν/cm–1: 1704 (C=O), 1740 (C=O), 3428 (NH).
1Н NMR, δ: 1.60 (s, 6 Н, 2 MeC=); 1.68 (s, 3 Н, MeC=);
1.80—2.15 (m, 5 H, 2 СH2, =CHСHH); 2.30—2.60 (m, 5 H,
2 СH2, =CHСHH); 3.72 (s, 3 H, OMe); 5.01 (t, 2 Н, 2 =СН,
J = 7.3 Hz); 6.29 (br.s, 1 Н, NH). 13C NMR, δ: 16.2, 17.7, 25.6
(all MeC=); 26.3, 29.9, 30.0 (all CH2CH=, CH2C=O); 37.4
(CH2); 39.8 (CH2C=); 52.5 (OMe); 66.0 (CCO2Me); 116.6,
123.9 (both =CH); 131.7, 140.8 (both =CMe2); 173.9, 177.2
(both C=O).
Dimethyl 2ꢀ(3ꢀmethylbutꢀ2ꢀenyl)ꢀ2ꢀnitropentanedioate (3n).
Colorless oil. Found (%): C, 52.92; H, 6.88; N, 4.95.
C12H19NO6. Calculated (%): C, 52.74; H, 7.01; N, 5.13.
13C NMR, δ: 18.0, 28.7 (both Me); 26.1 (CH2); 28.9 (C(3));
33.7 (C(4)); 51.9, 53.3 (both OMe); 94.8 (C(2)); 114.4 (=CH);
138.7 (=CMe2); 166.9 (C(1)); 172.1 (C(5)).
Methyl (E)ꢀ5,9ꢀdimethylꢀ2ꢀnitroꢀ2ꢀ(3ꢀoxopropyl)decaꢀ4,8ꢀ
dienoate (3o). Colorless oil. Found (%): C, 61.49; H, 7.93;
N, 4.68. C16H25NO5. Calculated (%): C, 61.72; H, 8.09; N, 4.50.
13C NMR, δ: 19.2, 20.7, 25.1 (all MeC=); 28.0, 28.4, 28.6, 31.9,
39.9 (all СН2); 54.5 (OMe); 93.9 (C(2)); 112.6 (C(4)), 121.4
(C(8)); 129.4 (C(9)); 142.4 (C(5)); 162.7 (C(1)); 193.4 (C=O).
Dimethyl 2ꢀ((E)ꢀ3,7ꢀdimethyloctaꢀ2,6ꢀdienyl)ꢀ2ꢀnitropenꢀ
tanedioate (3p). Colorless oil. Found (%): C, 60.15; H, 8.11;
N, 3.97. C17H27NO6. Calculated (%): C, 59.81; H, 7.97; N, 4.10.
13C NMR, δ: 16.3, 17.7, 25.7 (all MeC=); 26.3, 28.7 (CH2CH=);
28.8 (C(3)); 33.4, 33.5 (both C(4)); 39.8 (CH2); 51.9, 53.3
(both OMe); 94.8 (C(2)); 114.4, 123.6 (both =CH); 131.8
(=CMe2); 142.3 (=C(Me)CH2); 166.9 (C(1)); 172.1 (C(5)).
Recovery and recycle of KHCO3—[bmim][BF4] catalytic sysꢀ
tem in the Michael reaction between compounds 1 and 2. New
portions of reagents 1 and 2 (10 mmol each) were added to a
mixture of KHCO3 and [bmim][BF4] left after the extraction of
adduct 3, and further reaction was carried out as described above
(see Table 2, entries 1, 3, 12, 13, and 15). After the reaction was
repeated five times, KHCO3 (0.30 g, 3 mmol) was added to the
residue and the activated catalyst was used again. After the reacꢀ
This work was financially supported by the Russian
Foundation for Basic Research (Projects No. 05ꢀ03ꢀ08175
and No. 06ꢀ03ꢀ32603).
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Received April 10, 2007