Reactions of 2-diaminomethylidenecyclohexane-1,3-diones with diethyl malonate

Article abstract of DOI:10.1007/s11172-011-0021-2

The debenzoylation of 2-[(amino)(benzoylamino)methylidene]cyclohexane-1,3- diones (addition products of cyclohexane-1,3-diones with benzoylcyanamide) affords the corresponding 2-diaminomethylidenecyclohexane-1,3-diones. The latter act as N,N-dinucleophile

Full text of DOI:10.1007/s11172-011-0021-2

Russian Chemical Bulletin, International Edition, Vol. 60, No. 1, pp. 148—152, January, 2011
148
Reactions of 2ꢀdiaminomethylidenecyclohexaneꢀ1,3ꢀdiones
with diethyl malonate
V. A. Voronkova, A. V. Komkov, A. S. Shashkov, and V. A. Dorokhov
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: vador@ioc.ac.ru
The debenzoylation of 2ꢀ[(amino)(benzoylamino)methylidene]cyclohexaneꢀ1,3ꢀdiones
(addition products of cyclohexaneꢀ1,3ꢀdiones with benzoylcyanamide) affords the correspondꢀ
ing 2ꢀdiaminomethylidenecyclohexaneꢀ1,3ꢀdiones. The latter act as N,Nꢀdinucleophiles in
reactions with diethyl malonate in the presence of MeONa to form 6ꢀhydroxyꢀ2ꢀ(2,6ꢀdioxoꢀ
cyclohexylidene)ꢀ1,2ꢀdihydropyrimidinꢀ4(3H)ꢀones. This reaction performed at 200 °C in the
absence of bases results in the subsequent selfꢀcondensation of the dihydropyrimidinones to
give 4,5´ꢀbipyrimidine derivatives.
Key words: cyclohexaneꢀ1,3ꢀdiones, 2ꢀdiaminomethylidenecyclohexaneꢀ1,3ꢀdiones, diethyl
malonate, 1,2ꢀdihydropyrimidinꢀ4(3H)ꢀones, N,Nꢀdinucleophiles, 4,5´ꢀbipyrimidines, conꢀ
densation.
In the last two—three decades, a series of new pharꢀ
struction of heterocyclic systems only in the form of boron
chelate complexes.17—19
maceuticals with antitumor, antiviral, antiꢀinflammatoꢀ
ry, antibacterial, etc. activities were developed based on
pyrimidine derivatives (see the review1). This gave considꢀ
erable impetus to the elaboration of novel procedures and
the search for effective reactants for the synthesis of new
functionalized pyrimidines (see, for example, Refs 2—9).
Earlier, we have described new reactants for the synꢀ
thesis of pyrimidines, such as diaminomethylidene derivꢀ
atives of acyclic βꢀdiketones and βꢀketo esters unsubstiꢀ
tuted at the nitrogen atoms.10—12 For example, 2ꢀdiaminoꢀ
methylideneꢀ3ꢀoxoalkanoic acid esters act as functionalꢀ
ized amino enones in reactions with aryl isocyanates and
trichloroacetonitrile to give the corresponding esters of
4ꢀaminopyrimidineꢀ5ꢀcarboxylic acids.11,12 However, diꢀ
aminomethylidene derivatives of dibenzoylmethane and
acetoacetic ester act as N,Nꢀdinucleophiles in reactions
with aroylketenes generated in situ from 6ꢀarylꢀ2,2ꢀdiꢀ
methylꢀ1,3ꢀdioxinꢀ4ꢀones to form the corresponding
pyrimidinꢀ4ꢀones.10
Cyclic βꢀdiketones and their derivatives have found
wide use in the synthesis of fused pyrimidines.13—15 In
continuation of our investigations, we studied the reaction
of diethyl malonate with 2ꢀdiaminomethylidenecyclohexꢀ
aneꢀ1,3ꢀdiones in a purpose to synthesize new substituted
pyrimidines.
Earlier,16 we have prepared Nꢀbenzoylketene aminals
1a,b by the reactions of benzoylcyanamide with cycloꢀ
hexaneꢀ1,3ꢀdione and dimedone in the presence of Ni(OAc)2.
However, since compounds 1a,b contain the NH2 group
with low nucleophilicity, we have used them for the conꢀ
In the present study, we showed that compounds 1a,b
are easily debenzoylated with MeONa in MeOH to give
nitrogenꢀunsubstituted 2ꢀdiaminomethylidenecyclohexꢀ
aneꢀ1,3ꢀdiones 2a,b (Scheme 1). We expect that these
compounds would exhibit higher activity toward electroꢀ
philic reagents compared to their benzoyl derivatives.
Aminals 2a,b are white crystalline compounds, which
are readily soluble in MeOH, DMSO, and acetone and
moderately soluble in chloroform. The EI mass spectra of
2a,b have intense molecular ion peaks. The 1H NMR specꢀ
tra (DMSOꢀd6) of these compounds provide evidence for
the symmetrical structure of the dioxocyclohexane moiety
and show two broadened singlets for NH groups of twoꢀ
proton intensity at δ ~7.1—7.6 and ~10.0.
We found that aminals 2a,b can react with diethyl maꢀ
lonate as N,Nꢀdinucleophiles. The reactions of these comꢀ
pounds in MeOH in the presence of MeONa under reflux
give condensation products in the form of sodium salts
3a,b. The treatment of the latter with dilute hydrochloric
acid affords 6ꢀhydroxyꢀ2ꢀ(2,6ꢀdioxocyclohexylidene)ꢀ1,2ꢀ
dihydropyrimidinꢀ4(3H)ꢀones 4a,b. Salts 3a,b remain inꢀ
tact when treated with acetic acid, which is indicative of
the relatively strong acidic properties of compounds 4a,b.
Sodium salts 3a,b are white crystalline compounds,
which are readily soluble in water and insoluble in MeOH,
whereas compounds 4a,b are readily soluble in ethanol
and poorly soluble in water. Cyclohexylidenepyrimidines
4a,b were synthesized as crystal hydrates containing water
(two molecules according to elemental analysis data),
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 141—145, January, 2011.
1066ꢀ5285/11/6001ꢀ148 © 2011 Springer Science+Business Media, Inc.

2ꢀ(2,6ꢀDioxocyclohexylidene)pyrimidinꢀ4ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 1, January, 2011
149
Scheme 1
obtained, the structure containing the dicarbonylmethylꢀ
ene moiety was assigned to the reaction product.
We attempted to perform the condensation of ketene
aminals 2a,b with diethyl malonate in the absence of bases.
In this case, the reaction proceeded only at 200 °C, i.e.,
under much more drastic conditions, and gave products,
which were identified as 4,5´ꢀbipyrimidines 5a,b based on
the mass spectrometry and NMR spectroscopy data
(Scheme 2).
Scheme 2
´´´
´´´
R = H (a), Me (b)
Reagents and conditions: i. MeONa, MeOH, 20 °C;
ii. CH2(COOEt)2, MeONa, MeOH, Δ; iii. HCl.
R = H (a), Me (b)
which can easily be removed by drying in vacuo at 120 °C.
The structures of compounds 3 and 4 were confirmed by
spectroscopic methods. The EI mass spectra of pyrimꢀ
idines 4a,b have intense molecular ion peaks. The 1H NMR
spectra (DMSOꢀd6) of these compounds, like those of
salts 3, show a singlet for the proton H(5) of the pyrimiꢀ
dine moiety. The signals of two CH2CO groups of the
Reagents and conditions: i. CH2(COOEt)2, 200 °C; ii. Ph2O,
250 °C.
Apparently, under these conditions pyrimidines 4a,b
that are initially formed can undergo selfꢀcondensation
accompanied by the elimination of water. This is supportꢀ
ed by experimental data. In fact, compound 4b gives dimer
5b under reflux in diphenyl oxide or diethyl malonate.
Compounds 5a,b are solids, which are soluble only in
DMSO and water upon heating. The highꢀresolution ESI
mass spectra of bipyrimidines 5a,b have the ion peaks
[M + H]+ (the EI mass spectra did not show these peaks
due, apparently, to the low volatility of these compounds).
1
cyclohexane ring are equivalent in the H and 13C NMR
spectra. In addition, the signals of two NH groups
(1H NMR) and the C(4) and C(6) atoms (13C NMR) of
the pyrimidine ring are also identical. This confirms the
more uniform electron density distribution in salts 3 and
the fast hydroxyl proton transfer in compounds 4. In the
1H NMR spectra (DMSOꢀd6) of pyrimidines 4, the sigꢀ
nals for H(5) (δ ~5.1) and NH (δ ~13.8—13.9) are obꢀ
served at much lower field than the corresponding singlets
in the spectra of their salts 3 (δ ~4.2 and ~12.6, respectively).
It should be noted that the condensation of diaminoꢀ
methylidenemalononitrile with diethyl malonate was reꢀ
ported in the study,20 but, since the NMR data were not
1
In the H and 13C NMR spectra (DMSOꢀd6) of comꢀ
pounds 5a,b, the signals of ethoxy groups are absent, but
the spectra show signals corresponding to two cyclohexane
1
rings. The H NMR spectrum (DMSOꢀd6) shows a sinꢀ
1
glet for H(5´) at δ 7.27 (in the 2D H/13C HSQC specꢀ
trum, this hydrogen has a crossꢀpeak with the C(5´) atom
at δ 99.36), a broadened singlet for the protons NH(1) and

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Voronkova et al.
δ
δ
–260
–260
–250
–240
–230
–220
–210
–250
–240
–230
–220
–210
15
14
13
12
11
10
9
8
δ
Fig. 1. 2D 1H/15N HMBC spectrum of compound 5b.
NH(3) at δ 12.95, and broadened singlets of oneꢀproton
intensity for NH(3´) and NH(1´) at δ 14.39 and 15.20,
respectively. In the 13C NMR spectrum (DMSOꢀd6), like
in the spectra of compounds 4a,b, the signals for C(4) and
Experimental
The 1H NMR spectra were recorded on a Bruker AMꢀ300
instrument operating at 300 MHz. The 13C NMR spectra and
the 2D 1H/13C and 1H/15N HMBC spectra were measured on
a Bruker Avance 600 instrument (600, 150, and 60.8 MHz for 1H,
13C, and 15N, respectively). The signals of the residual protons
of the deuterated solvent (7.27 ppm for CDCl3 and 2.50 ppm for
DMSOꢀd6) were used as the references in the 1H NMR spectra;
the multiplet of DMSOꢀd6 (39.50 ppm) was used as the internal
standard in the 13C NMR spectra. The 15N chemical shifts were
measured relative to MeNO2 as the internal standard (highꢀfield
chemical shifts are given with a minus sign). The IR spectra were
recorded on a SpecordꢀM 82 instrument. The mass spectra were
measured on a Kratos MSꢀ30 instrument (EI, 70 eV, the temperꢀ
ature of the ionization chamber was 250 °C, direct inlet). The
highꢀresolution mass spectra were obtained on a Bruker
micrOTOF II instrument using the electrospray ionization (ESI)
technique27 in the positiveꢀion mode (capillary voltage was 4500 V).
The mass scan range was m/z 50—3000 D; the external and
internal calibration was performed (Electrospray Calibrant Soꢀ
lution, Fluka); solutions of samples in acetonitrile were introꢀ
1
C(6) are equivalent (δ 160.6). In the 2D H/13C HMBC
spectrum (DMSOꢀd6), the following crossꢀpeaks are obꢀ
served: of the proton H(5´) (7.27 ppm) with the carbon
atoms C(5) (85.95 ppm) and C(5´) (99.36 ppm), of the
protons NH(1) and NH(3) (12.95 ppm) with the carbon
atoms C(5) (85.95 ppm) and C(1″) (94.09 ppm), and
of the proton NH(1´) (15.20 ppm) with the carbon
atoms C(5´) (99.36 ppm), C(5) (85.95 ppm), and C(1´´´ )
(95.50 ppm). In the 2D 1H/15N HMBC spectrum (Fig. 1),
there are oneꢀbond crossꢀpeaks of the protons with the
nitrogen atoms (δH/δN, ppm): 15.20/–246, H(1´)/N(1´);
14.39/–223, H(3´)/N(3´); 12.95/–232, H(1,3)/N(1,3).
There are also threeꢀbond crossꢀpeaks of the proton H(5´)
(δH 7.27) with the nitrogen atom N(1´) (δN –246 ppm), of
the proton H(1) with the nitrogen atom N(3), and/or,
on the contrary, of the proton H(3) with the nitrogen
atom N(1).
Numerous biheterocycles have received considerable
attention in organic chemistry (see the review21). Among
these compounds, bipyrimidines with different structures
have attracted attention as multidentate ligands and are
used in the chemistry of coordination compounds (see, for
example, the studies22—26).
To sum up, we showed that ketene aminals 2a,b can be
involved in the heterocyclization as N,Nꢀdinucleophiles
and, apparently, can be used in reactions with other diꢀ
electrophilic reagents (diketones, oxocarboxylic acid esꢀ
ters, etc.).
duced by the syringe injection; the flow rate was 3 μL min–1
;
nitrogen was used as the nebulizing gas (4 L min–1); the temperꢀ
ature of the interface was 180 °C. Diethyl malonate (Lancaster)
and methanol were subjected to fractional distillation prior to
use. Ketene aminals 1a,b were synthesized according to a known
procedure.16
2ꢀDiaminomethylidenecyclohexaneꢀ1,3ꢀdione (2a). A solution
of MeONa in MeOH (1.5 mL, 1.9 mmol) was added to a soluꢀ
tion of ketene aminal 1a (0.5 g, 1.9 mmol) in MeOH (10 mL).
The reaction mixture was stirred for 30 min and acidified with
AcOH. Then the solution was concentrated in vacuo to dryness.
Chloroform was added to the residue, and AcONa that remained
undissolved was filtered off. The filtrate was concentrated, peꢀ

2ꢀ(2,6ꢀDioxocyclohexylidene)pyrimidinꢀ4ꢀones
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 1, January, 2011
151
troleum ether was added, and the precipitate that formed was
filtered off. The yield was 0.27 g (90%), m.p. 244—245 °C.
Found (%): C, 54.32; H, 6.51; N, 18.30. C7H10N2O2. Calculatꢀ
ed (%): C, 54.54; H, 6.54; N, 18.17. MS, m/z (Irel (%)): 154
[M]+ (100), 126 [M – CO]+ (89), 113 [M – CHCO]+ (26), 85
[M – CHCO – CO]+ (54), 84 [M – CH2CO – CO]+ (87). IR
(KBr), ν/cm–1: 3416 (NH), 3340, 3250—2880 (NH, CH), 1616,
1568. 1H NMR (DMSOꢀd6), δ: 1.73 (m, 2 H, CH2); 2.29 (t, 4 H,
2 CH2, J = 6.0 Hz); 7.64 (br.s, 2 H, 2 NH); 10.00 (br.s, 2 H, 2 NH).
2ꢀDiaminomethylideneꢀ5,5ꢀdimethylcyclohexaneꢀ1,3ꢀdione
(2b) was synthesized analogously to compound 2a from ketene
aminal 1b. The yield was 95%, m.p. 190—192 °C. Found (%):
C, 59.15; H, 7.69; N, 15.45. C9H14N2O2. Calculated (%):
C, 59.32; H, 7.74; N, 15.37. MS, m/z (Irel (%)): 182 [M]+ (80),
154 [M – CO]+ (19), 139 [M – CO – Me]+ (19), 126 [M – 2 CO]+
(53), 98 (53), 83 (100). IR (KBr), ν/cm–1: 3336 (NH),
3330—2870 (NH, CH), 1624, 1584. 1H NMR (DMSOꢀd6), δ:
0.94 (s, 6 H, 2 Me); 2.20 (s, 4 H, 2 CH2); 7.14 (br.s, 2 H, 2 NH);
10.04 (br.s, 2 H, 2 NH).
(28), 194 [M – 2 CO]+ (11), 166 [M – 3 CO]+ (43), 153
[M – CHCO – 2 CO]+ (45), 138 (21). IR (KBr), ν/cm–1: 3392
(NH), 3300—2860 (NH, CH), 1640, 1572. 1H NMR (DMSOꢀd6),
δ: 0.99 (s, 6 H, 2 Me); 2.39 (s, 4 H, 2 CH2); 5.07 (s, 1 H, CH);
13.83 (br.s, 2 H, 2 NH). 13C NMR (DMSOꢀd6), δ: 27.62 (CMe2);
30.16 (CMe2); 50.60 (2 CH2); 84.61 (C(5)); 94.93 (C(CO)2);
154.94 (C(2)); 160.26 (C(4), C(6)); 197.93 (2 CO).
6ꢀHydroxyꢀ2ꢀ(2,6ꢀdioxocyclohexylidene)ꢀ5ꢀ[4ꢀoxoꢀ2ꢀ(2,6ꢀ
dioxocyclohexylidene)ꢀ1,2,3,4ꢀtetrahydropyrimidinꢀ6ꢀyl]ꢀ1,2ꢀdiꢀ
hydropyrimidinꢀ4(3H)ꢀone (5a). Diethyl malonate (1.5 mL) was
added to ketene aminal 2a (0.1 g, 0.65 mmol). The reaction
mixture was refluxed for 2.5 h and then cooled. The precipitate
was filtered off, washed with boiling MeOH, and dried. The
yield of bipyrimidine 5a was 0.09 g (64%), m.p. >300 °C.
Found (%): C, 55.99; H, 4.28; N, 12.83. C20H18N4O7. Calculatꢀ
ed (%): C, 56.34; H, 4.26; N, 13.14. Highꢀresolution mass specꢀ
trum (HRꢀMS): Found: m/z 427.1241 [M + H]+. C20H18N4O7.
Calculated: [M + H]+ = 427.1248. IR (KBr), ν/cm–1: 3430
(NH), 3100—2850 (NH, CH), 1700—1500. 1H NMR (DMSOꢀd6),
δ: 1.83 (m, 4 H, 2 CH2); 2.44 (m, 8 H, 4 CH2CO); 7.27 (s, 1 H,
H(5´)); 13.02 (br.s, 2 H, NH(1), NH(3)); 14.46 (br.s, 1 H,
NH(3´)); 15.22 (br.s, 1 H, NH(1´)).
6ꢀHydroxyꢀ2ꢀ(2,6ꢀdioxocyclohexylidene)ꢀ1,2ꢀdihydropyrimꢀ
idinꢀ4(3H)ꢀone (4a). Diethyl malonate (0.29 mL, 1.95 mmol)
and a solution of MeONa in MeOH (1.5 mL, 1.95 mmol) were
added to a solution of ketene aminal 2a (0.1 g, 0.65 mmol) in
MeOH (5 mL). The reaction mixture was refluxed for 1.5 h. The
precipitate that formed was filtered off and washed with MeOH.
The white precipitate that formed was dissolved in water (7 mL),
and then dilute HCl (1 : 1) was added to the solution. The preꢀ
cipitate that formed was filtered off, successively washed with
water and diethyl ether, and dried in vacuo at 120 °C. Compound
4a was obtained in a yield of 0.14 g (95%), m.p. >300 °C.
Found (%): C, 53.91; H, 4.45; N, 12.55. C10H10N2O4. Calculatꢀ
ed (%): C, 54.06; H, 4.54; N, 12.61. MS, m/z (Irel (%)): 222
[M]+ (100), 194 [M – CO]+ (17), 152 [M – CH2CO – CO]+
6ꢀHydroxyꢀ2ꢀ(4,4ꢀdimethylꢀ2,6ꢀdioxocyclohexylidene)ꢀ5ꢀ[2ꢀ
(4,4ꢀdimethylꢀ2,6ꢀdioxocyclohexylidene)ꢀ4ꢀoxoꢀ1,2,3,4ꢀtetraꢀ
hydropyrimidinꢀ6ꢀyl]ꢀ1,2ꢀdihydropyrimidinꢀ4(3H)ꢀone (5b). A.
Bipyrimidine 5b was synthesized analogously to compound 5a
from ketene aminal 2b and diethyl malonate. The yield was 54%,
m.p. >300 °C. Found (%): C, 59.34; H, 5.54; N, 11.60. C24H26N4O7.
Calculated (%): C, 59.74; H, 5.43; N, 11.61. Highꢀresolution
mass spectrum (HRꢀMS): Found: m/z 483.1858 [M + H]+.
C24H26N4O7. Calculated: [M + H]+ = 483.1874. IR (KBr),
ν/cm–1: 3440 (NH), 3150—2860 (NH, CH), 1700—1500. 1H NMR
(DMSOꢀd6), δ: 0.99 (s, 12 H, 4 Me); 2.35 (s, 4 H, 2 CH2); 2.36
(s, 4 H, 2 CH2); 7.27 (s, 1 H, H(5´)); 12.95 (br.s, 2 H, NH(1),
NH(3)); 14.39 (br.s, 1 H, NH(3´)); 15.20 (br.s, 1 H, NH(1´)).
13C NMR (DMSOꢀd6), δ: 27.75 (CMe2); 27.77 (CMe2); 29.97,
30.03 (C(4″), C(4´´´ )); 51.10, 51.21 (C(3″), C(5″), C(3´´´ ),
C(5´´´ )); 85.95 (C(5)); 94.09 (C(1″)); 95.50 (C(1´´´ )); 99.36 (C(5´));
149.84 (C(6´)); 153.42, 154.53 (C(2), C(2´)); 159.33 (C(4´)), 160.62
(C(4), C(6)); 196.21, 197.77 (C(2″), C(6″), C(2´´´ ), C(6´´´ )).
B. A mixture of compound 4b (0.1 g) and diphenyl oxide (1.0 g)
was refluxed for 20 min and then cooled to 20 °C. Petroleum
ether (15 mL) was added to the reaction mixture. The precipiꢀ
tate that formed was filtered off and washed with methanol
(5 mL). Compound 5b was obtained in a yield of 0.07 g (69%).
(57), 139 [M – CH2CO – CHCO]+ (44). IR (KBr), ν/cm–1
:
3436 (NH), 3310—2870 (NH, CH), 1676, 1630—1600, 1560.
1H NMR (DMSOꢀd6), δ: 1.84 (m, 2 H, CH2); 2.48 (t, 4 H,
2 CH2, J = 6.0 Hz); 5.09 (s, 1 H, CH); 13.93 (br.s, 2 H, 2 NH).
6ꢀHydroxyꢀ2ꢀ(4,4ꢀdimethylꢀ2,6ꢀdioxocyclohexylidene)ꢀ1,2ꢀ
dihydropyrimidinꢀ4(3H)ꢀone (4b). Diethyl malonate (0.25 mL,
1.65 mmol) and a solution of MeONa in MeOH (1.6 mL,
1.65 mmol) were added to a solution of ketene aminal 2b (0.1 g,
0.55 mmol) in MeOH (5 mL). The reaction mixture was reꢀ
fluxed for 1.5 h. The precipitate that formed was filtered off and
washed with MeOH. Sodium salt 3b was obtained in a yield of
0.14 g (93%), m.p. >300 °C. IR (KBr), ν/cm–1: 3430 (NH),
3200—2850 (NH, CH), 1700 (CO), 1608. 1H NMR (DMSOꢀd6),
δ: 0.97 (s, 6 H, 2 Me); 2.30 (s, 4 H, 2 CH2); 4.20 (s, 1 H, CH);
12.61 (br.s, 2 H, 2 NH). 13C NMR (DMSOꢀd6), δ: 27.78 (CMe2);
30.02 (CMe2); 51.19 (2 CH2); 81.07 (C(5)); 94.53 (C(CO)2);
154.60 (C(2)); 161.54 (C(4), C(6)); 196.58 (2 CO). The assignꢀ
ment of the signals was made based on the 2D 1H/13C HMBC
spectrum. The resulting salt was dissolved in water (7 mL), and
dilute HCl (1 : 1) was added to the solution. The precipitate that
formed was filtered off and successively washed with water and
diethyl ether. Dihydrate of compound 4b was obtained. Found
(%): C, 50.02; H, 6.28; N, 9.65. C12H14N2O4•2 H2O. Calculatꢀ
ed (%): C, 50.35; H, 6.34; N, 9.79. The dihydrate was dried
in vacuo at 120 °C, and compound 4b was obtained in a yield of
0.09 g (62%), m.p. 187—188 °C. Found (%): C, 57.43; H, 5.58;
N, 11.01. C12H14N2O4. Calculated (%): C, 57.59; H, 5.64;
N, 11.19. MS, m/z (Irel (%)): 250 [M]+ (100), 222 [M – CO]+
1
The H NMR spectrum of this compound was identical to that
of the product prepared according to the method A.
C. A mixture of compound 4b (0.1 g) and diethyl malonate
(1.5 mL) was refluxed for 2 h, during which the reaction mixture
turned homogeneous and then the precipitate gradually formed.
The reaction mixture was cooled to 20 °C. The precipitate was
filtered off and washed with petroleum ether and methanol
(3 mL). Compound 5b was obtained in a yield of 0.04 g (42%).
The 1H NMR spectrum of this compound was identical to those
of the products prepared according to the methods A and B.
This study was financially supported by the Russian
Academy of Sciences (Program for Basic Research of the
Presidium of the Russian Academy of Sciences "Developꢀ
ment of Methods for the Synthesis of Chemical Comꢀ
pounds and the Design of New Materials").

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Received September 3, 2010