Synthesis of 8-aroylpyrrolo[1,2-a]pyrazine-1,6,7(2H)-triones and their reaction with water. New analogs of cyclic dipeptides

Article abstract of DOI:10.1134/S1070428015110123

2-Aryl-8-aroyl-3,4-dihydropyrrolo[1,2-a]pyrazine-1,6,7(2H)-triones prepared from (Z)-1-aryl-3-(2-aryl-2-oxoethylidene)piperazin-2-ones and oxalyl chloride react with water to afford (E)-8a-hydroxy-2-aryl-8-[aryl(hydroxy)methylene]tetrahydropyrrolo[1,2-a]p

Full text of DOI:10.1134/S1070428015110123

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2015, Vol. 51, No. 11, pp. 1587–1592. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © A.V. Chervyakov, P.A. Slepukhin, M.V. Dmitriev, A.N. Maslivets, 2015, published in Zhurnal Organicheskoi Khimii, 2015, Vol. 51,
No. 11, pp. 1617–1622.
Synthesis of 8-Aroylpyrrolo[1,2-a]pyrazine-1,6,7(2H)-triones
and Their Reaction with Water. New Analogs
of Cyclic Dipeptides
A. V. Chervyakova, P. A. Slepukhinb, M. V. Dmitrieva, and A. N. Maslivetsa
a Perm State National Research University, ul. Bukireva 15, Perm, 614990 Russia
e-mail: koh2@psu.ru
b Postovskii Institute of Organic Synthesis, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia
Received February 25, 2015
Abstract—2-Aryl-8-aroyl-3,4-dihydropyrrolo[1,2-a]pyrazine-1,6,7(2H)-triones prepared from (Z)-1-aryl-3-(2-
aryl-2-oxoethylidene)piperazin-2-ones and oxalyl chloride react with water to afford (E)-8а-hydroxy-2-aryl-8-
[aryl(hydroxy)methylene]tetrahydropyrrolo[1,2-a]pyrazine-1,6,7(2H)-triones. The crystal and molecular
structure of 8-benzoyl-2-phenyl-3,4-dihydropyrrolo[1,2-a]pyrazine-1,6,7(2H)-trione and (E)-8а-hydroxy-8-
[hydroxy(phenyl)methylene]-2-phenyltetrahydropyrrolo[1,2-a]pyrazine-1,6,7(2H)-trione were studied by X-ray
diffraction analysis.
DOI: 10.1134/S1070428015110123
Heterocyclic enaminoketones reacting with oxalyl
chloride afford hetareno[е]pyrrole-2,3-diones [1–4] or
4-heterylfuran-2,3-diones [4, 5]. In order to extend the
range of data providing a possibility to predict the
occurrence of one or another of these two routes we
synthesized (Z)-1-aryl-3-(2-aryl-2-oxoethylidene)pipe-
razin-2-ones 1a–1c and investigated their reactions
with oxalyl chloride.
In 1H NMR spectra of compounds 1a–1c along with
the signals of aromatic protons and the protons of the
methyl group (for compound 1b) two multiplets appear
of the protons of two methylene groups in the region
3.69–3.97 ppm, a singlet from the proton of vinyl
group СН (6.57–6.63 ppm), and a broadened singlet in
the downfield region 10.86–10.88 ppm from the proton
of NH group involved in the formation of the intra-
molecular hydrogen bond.
Piperazinones 1a–1c were prepared from methyl 4-
aryl-2-hydroxy-4-oxobut-2-enoates and N-arylethyle-
nediamines in toluene in the presence of catalytic
quantities of glacial acetic acid by boiling for 1 h. The
use of toluene as solvent made it possible to reduce the
reaction time and slightly increase the yield of target
products as compared with the known procedure of
piperazinone 1c synthesis in ethanol [6].
The spectral characteristics of compounds 1a–1c
show that they exist in the crystalline state and in
solutions with a strong intramolecular hydrogen bond
of H-chelate type between the NH group and the aroyl
group, i.e. in the form of Z-isomers characteristic of
the compounds of this class [6].
The reactions of compounds 1a–1c with oxalyl
chloride in toluene (1 h at room temperature and 2–2.5 h
of boiling till the end of HCl liberation under the
common conditions for the synthesis of five-membered
dioxoheterocycles [7]) furnished instead of expected 4-
heterylfuran-2,3-diones 2-aryl-8-aroyl-3,4-dihydropyr-
rolo[1,2-a]pyrazine-1,6,7(2H)-triones 2a–2c, [8], whose
structure was confirmed by XRD analysis by an
example of compound 2a.
Compounds 1a–1c are light-yellow high melting
crystalline substances readily soluble in DMF and
DMSO, sparingly soluble in ethanol, benzene, toluene,
insoluble in water and alkanes.
IR spectra of compounds 1a–1c contain the bands
of the stretching vibrations of the NH group as a broad
band in the region 3150–3214 cm–1, of lactam carbonyl
group (1668–1671 cm–1), and aroyl carbonyl group
(1603–1607 cm–1) involved in the formation of an
intramolecular hydrogen bond.
Pyrrolopyrazinetriones 2a–2c are bright red high
melting crystalline substances readily soluble in DMF
1587

CHERVYAKOV et al.
1588
COOMe
O
Ar1
N
Ar1
Ar1
N
H
.
.
.
.
.
.
O
N
O
O
O
H
O
Ar2
(COCl)2
_2HCl
H2O
O
OH
O
Ar1NHCH2CH2NH2
N
N
Δ
N
Ar2
Ar2
.
H
.
.
O
Ar2
O
O
O
1a_1c
2a_2c
3a_3c
Ar1 = Ar2 = Ph (a); Ar1 = C6H4Me-4, Ar2 = Ph (b); Ar1 = Ph, Ar2 = C6H4Cl-4 (c).
and DMSO, sparingly soluble in chloroform, benzene,
toluene, insoluble in alkanes; they react with water and
alcohols and quickly suffer discoloration at storage due
to the reaction with the air moisture.
According to XRD data on compound 2a (Fig. 1),
the five-membered heterocycle of the heterobicyclic
system is flat, and the six-membered ring is present in
the pseudo-sofa conformation. The benzoyl fragment
is virtually planar and turned at a considerable angle
with respect to the plane of the heterobicyclic system.
In the IR spectra of compounds 2a–2c the bands of
stretching vibration are present of lactam С6=O (1754–
1755 cm–1), C1=O (1663–1691 cm–1), ketone C7=O
(1721–1731 cm–1) and aroyl (1614–1665 cm–1) carbonyl
groups. The higher wave number corresponding to the
band of stretching vibrations of lactam group compared
to the band of ketone group is in agreement with the
published data on these groups in the IR spectra of
substituted furan-2,3-diones [9] and isatins [10].
As known, 4-acyl-substituted 1Н-pyrrole-2,3-
diones and hetareno[е]pyrrole-2,3-diones {3-
acylpyrrolo[2,1-с][1,4]benzoxazine-1,2,4-triones and
{3-acylpyrrolo[1,2-а]quinoxaline-1,2,4(5Н)-triones}
may reversibly add OН-nucleophiles (water and
alcohol) to the carbon atom in the position 5 of the 1Н-
pyrrole-2,3-dione ring giving the corresponding 4-
acyl-3,5-dihydroxy- and 5-alkoxy-4-acyl-3-hydroxy-
2,5-dihydro-1Н-pyrrol-2-ones [7].
1
In H NMR spectra of compounds 2a–2c solutions
along with the signals of aromatic protons a three-
proton singlet appears from the protons of the methyl
group at 2.28 ppm (in the spectrum of compound 2b),
and two multiplets of protons from two methylene
groups in the region 3.75–4.13 ppm.
At keeping 2-aryl-8-aroyl-3,4-dihydropyrrolo[1,2-
a]pyrazine-1,6,7(2H)-triones 2a–2c in toluene
saturated with water for 8–12 h (till discoloration) we
obtained (E)-2-aryl-8-[aryl(hydroxy)methylene]-8а-
hydroxytetrahydropyrrolo[1,2-a]pyrazine-1,6,7(2H)-
triones 3a–3c, whose structure was confirmed by XRD
analysis by an example of compound 3b.
C20
O4
C19
C18
O3
Compounds 3a–3c are light-yellow crystalline
substances melting with decomposition, readily soluble
in DMF and DMSO, sparingly soluble in chloroform,
benzene, toluene, insoluble in alkanes and water. The
light yellow solutions of compounds 3a–3c in glacial
acetic acid or DMSO at heating become bright red, and
the intensity of color grows proportionally to the
growing temperature, apparently due to the
reversibility of water addition to pyrrolopyrazine-
triones 2.
C14
C5
C15
C17
C16
O1
C6
C4
C7
C3
C8
N1
O2
N2
C2
C9
C10
C1
C11
The IR spectra of compounds 3a–3c contain the
bands of the stretching vibrations of the alcohol group
С8аOH as a narrow peak in the region 3185–3290 cm–1,
of enol group С8=С(Ar)OH involved in the formation
of the intramolecular hydrogen bond as a broad peak in
C13
C12
Fig. 1. Molecular structure of 8-benzoyl-2-phenyl-3,4-
dihydropyrrolo[1,2-a]pyrazine-1,6,7(2H)-trione 2a.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 11 2015

SYNTHESIS OF 8-AROYLPYRROLO[1,2-a]PYRAZINE-1,6,7(2H)-TRIONES
1589
O1
C10
C9
C19
C20
O3
C8
O2
C4
C21
C15
C11
N2
N1
C18
C5
C12
C3
C2
C6
C7
C17
C16
C13
C14
O5
C1
O4
Fig. 2. Molecular structure of (E)-8a-hydroxy-8-[hydroxy(phenyl)methylidene]-2-(4-tolyl)tetrahydropyrrolo[1,2-a]pyrazine-1,6,7(2H)-
trione 3b.
the region 3064–3079 cm–1, of carbonyl groups C6=O,
C7=O of the pyrroledione ring (1693–1723 cm–1), and
of lactam carbonyl group C1=O (1585–1603 cm–1)
involved in the formation of the intramolecular
hydrogen bond.
In 1H NMR spectra of compounds 3a–3c along with
the signals of aromatic protons two doublets of
doublets are present belonging to four protons of two
methylene groups in the region 3.90–4.11 ppm,
a broadened singlet of the proton of the alcohol
group С8аOH in the region 7.31–7.38 ppm, and a
three- proton singlet of the methyl group at 2.28 ppm
(in the spectrum of compound 3b) are observed. The
signal of enol group С8=С(Ar)OH involved in the
formation of the intramolecular hydrogen bond is
strongly broadened (9–13 ppm) and is not seen in the
spectrum.
positions with approximately 0.5 occupancy; it may be
described as the ring rotation around the C15–C18 axis
(this disordering is not shown in Fig. 2). The water
molecules are also disordered by two positions with
equal occupancy. The molecules in the crystal form an
infinite two-dimensional net parallel to the [0 0 1]
plane due to the developed system of intermolecular
hydrogen bonds involving the groups O2–Н2, C1=O4,
C2=O5 and water molecules.
Pyrrolopyrazinetriones 2a–2c react with water
adding OН groups to the carbon atom in the position 5 of
the 1Н-pyrrole-2,3-dione ring as has been previously ob-
served with 4-acyl-substituted 1Н-pyrrole-2,3-diones
[7], yet in the addition products 3a–3c the proton is
located not at the oxygen atom of the carbonyl group
in the position 3 of the 1Н-pyrrole-2,3-dione ring, but
at the oxygen atom of the aroyl group followed by the
formation of the intramolecular hydrogen bond of this
group with the oxygen atom of the carbonyl group in
the position 1of the pyrrolopyrazinetriones.
According to XRD data compound 3b crystallized
in a centrosymmetric space group in the form of a
hydrate in a ratio 1 : 2 (Fig. 2). The heterobicyclic
system is not planar, it is bent along the axis С11–С14.
The enol hydroxy group forms a strong intramolecular
hydrogen bond with the lactam carbonyl group
С12=O3. The tolyl substituent is disordered by two
The heating in capillary of compounds 3a–3c to the
temperatures close to the melting point (130–140°С)
led to water elimination and the formation of initial
pyrrolopyrazinetriones 2a–2c.
O
O
O
H
H
R
N
N
N
HN
HN
N
HN
HN
H
HO
H
H
O
OH
OH
O
O
Brevianamide U
Tryprostatins
Maculosin
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 11 2015

CHERVYAKOV et al.
1590
Thus we developed a new method of synthesis of
molecular hydrogen bond), 1670 (С2=O), 1605 br
1
functionalized heterobicyclic system of pyrrolo[1,2-a]-
pyrazine, analog of 2,5-diketopiperazine, the smallest
of known cyclic peptides. The natural 2,5-
diketopiperazines (brevianamides [11], tryprostatins
[12], maculosin [13], etc.), as well as synthetic N-
substituted pyrrolopyrazines exhibit antitumor,
phytotoxic, and other kinds of activity [14].
(COPh). Н NMR spectrum (DMSO-d6), δ, ppm: 2.31
s (3H, Me), 3.69 m (2H, C5H2), 3.91 m (2H, C6H2),
6.63 s (1H, С3=CH), 7.23 d (2H, Hm in C6H4Me-4, J
8.4 Hz), 7.31 d (2H, Ho in C6H4Me-4, J 8.4 Hz), 7.50
m (3Harom), 7.90 d (2H, Ho in СOPh, J 7.0 Hz), 10.88 s
(1H, NH). Found, %: C 74.35; H 5.95; N 9.20.
C19H18N2O2. Calculated, %: C 74.49; H 5.92; N 9.14.
(Z)-3-[2-Oxo-2-(4-chlorophenyl)ethylidene]-1-
phenylpiperazin-2-one (1c). Yield 80%, mp 201–202°С
(toluene). IR spectrum, ν, cm–1: 3213 br (NH in intra-
molecular hydrogen bond), 1668 (С2=O), 1603 br
EXPERIMENTAL
IR spectra were recorded on a spectrophotometer
Perkin Elmer Spectrum Two from mulls in mineral oil
or in perfluorinated oil. 1H NMR spectra were
registered on a spectrometer Bruker Avance III
(operating frequency 500 MHz), internal reference
TMS. Elemental analysis was carried out on an
analyzer vario MICRO cube. The homogeneity of
compounds synthesized was confirmed by TLC
(Silufol plates, eluents benzene–ethyl acetate, 5 : 1,
ethyl acetate, development in iodine vapor), the
optimization of the reaction conditions and registration
of mass spectra were performed by procedure ultra-
HPLC-MS, column Acquity UPLC C18 1.7 µm, mobile
phase acetonitrile–water, flow rate 0.3–0.6 mL/min,
detector ESI MS Xevo TQD, electrospray ionization in
the mode of positive ions registration ESI+, tempe-
rature 150°C, voltage on the capillary 3500 V, on the
cone 50 V.
1
(COС6Н4). Н NMR spectrum [(CD3)2CO)], δ, ppm:
3.67 m (2H, C5H2), 3.97 m (2H, C6H2), 6.57 s (1H,
С3=CH), 7.31 m (1Harom), 7.41–7.45 m (4Harom), 7.54 d
(2H, Hm in СOC6H4Cl-4, J 8.5 Hz), 7.90 d (2H, Ho in
СOC6H4Cl-4, J 8.5 Hz), 10.88 s (1H, NH). Found, %:
C 66.00; H 4.71; N 8.53. C18H15ClN2O2. Calculated,
%: C 66.16; H 4.63; N 8.57.
8-Benzoyl-2-phenyl-3,4-dihydropyrrolo[1,2-a]-
pyrazine-1,6,7(2H)-trione (2a). To a solution of 5.0 g
(17.1 mmol) of piperazinone 1a in 250 mL of anhyd-
rous toluene was added 2.2 mL (25.7 mmol) of oxalyl
chloride, the mixture was maintained for 1 h, boiled
for 2 h, and cooled. The solvent was distilled off in a
vacuum on a rotary evaporator. Yield 90%, mp 150–
151°С (toluene). IR spectrum, ν, cm–1: 1755 (С6=O),
1
1731 (C7=O), 1663 (C1=O), 1650 (COPh). Н NMR
spectrum (CDCl3), δ, ppm: 4.02 d.d (2H, C4H2, J 6.8,
4.2 Hz), 4.13 d.d (2H, C3H2, J 6.8, 4.2 Hz), 7.24–7.50
group of signals (7Harom), 7.57 t (1Harom), 7.87 d (2H,
Ho in СOPh, J 7.3 Hz). Found, %: C 69.42; H 4.09; N
8.03. C20H14N2O4. Calculated, %: C 69.36; H 4.07; N
8.09.
(Z)-3-(2-Oxo-2-phenylethylidene)-1-phenyl-pipe-
razin-2-one (1a). To 15.0 g (72.7 mmol) of methyl 4-
aryl-2-hydroxy-4-oxobut-2-enoate in a mixture of
100 mL of toluene and 40 mL of glacial acetic acid
was added 9.5 mL (72.7 mmol) of N-phenylethyle-
nediamine, and the reaction mixture was boiled for 1 h
(TLC monitoring), evaporated to 40 mL volume, the
precipitate was filtered off. Yield 92%, mp 154–156°С
(toluene). IR spectrum, ν, cm–1: 3214 br (NH in
intramolecular hydrogen bond), 1671 (С2=O), 1607 br
Compounds 2b and 2c were synthesized similarly.
8-Benzoyl-2-(4-tolyl)-3,4-dihydropyrrolo[1,2-a]-
pyrazine-1,6,7(2H)-trione (2b). Yield 70%, mp 147–
148°С (toluene). IR spectrum, ν, cm–1: 1755 (С6=O),
1
(COPh). Н NMR spectrum (DMSO-d6), δ, ppm: 3.70
1
1726 (C7=O), 1672 (C1=O), 1660 (COPh). Н NMR
m (2H, C5H2), 3.97 m (2H, C6H2), 6.60 s (1H, С3=CH),
7.31 m (1Harom), 7.42–7.56 group of signals (7Harom),
7.89 d (2H, Ho in СOPh, J 6.8 Hz), 10.86 s (1H, NH).
Found, %: C 73.83; H 5.38; N 9.65. C18H16N2O2.
Calculated, %: C 73.95; H 5.52; N 9.58.
spectrum (CDCl3), δ, ppm: 2.30 s (3H, Me), 3.75–4.05
group of signals (4H, CH2CH2), 7.07–7.87 group of
signals (9Harom). Found, %: C 70.09; H 4.42; N 7.74.
C21H16N2O4. Calculated, %: C 69.99; H 4.48; N 7.77.
2-Phenyl-8-(4-chlorobenzoyl)-3,4-dihydropyr-
rolo[1,2-a]pyrazine-1,6,7(2H)-trione (2c). Yield
77%, mp 147–149°С (toluene). IR spectrum, ν, cm–1:
1755 (С6=O), 1721 (C7=O), 1691 (C1=O), 1665
Compounds 1b and 1c were synthesized similarly.
(Z)-3-(2-Oxo-2-phenylethylidene)-1-(4-tolyl)pi-
perazin-2-one (1b). Yield 89%, mp 177–178°С
(toluene). IR spectrum, ν, cm–1: 3150 br (NH in intra-
1
(COС6H4). Н NMR spectrum (DMSO-d6), δ, ppm:
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 11 2015

SYNTHESIS OF 8-AROYLPYRROLO[1,2-a]PYRAZINE-1,6,7(2H)-TRIONES
1591
3.83 m (2H, C4H2), 4.04 m (2H, C3H2), 7.20–7.39 m
(5H, Ph), 7.50 d (2H, Hm in СOС6H4Cl-4, J 8.5 Hz),
7.96 d (2H, Ho in СOС6H4Cl-4, J 8.5 Hz). Found, %: C
63.24; H 3.30; N 7.34. C20H13ClN2O4. Calculated, %:
C 63.09; H 3.44; N 7.36.
X-ray diffraction study. Unit cell parameters and
the array of experimental reflections of single crystals
of compound 2a and 3b were measured on automatic
four-circle diffractometers with CCD-detectors
Xcalibur S (2a) and Xcalibur R (3b) by the method of
ω-2θ-scanning with
a
monochromatized MoKα-
(E)-8a-Hydroxy-8-[hydroxy(phenyl)methyl-
idene]-2-phenyltetrahydropyrrolo[1,2-a]pyrazine-
1,6,7(2H)-trione (3a). A beaker with a solution of 0.50 g
(1.40 mmol) of pyrrolopyrazinetrione 2a in 20 mL of
toluene and a beaker with 50 mL of heated to boiling
water were placed in a vacuum desiccator, the air was
pumped out, and the desiccator was left standing for 12 h.
Yield 95%, mp 147–149°С (decomp., toluene). IR
spectrum, ν, cm–1: 3290 (С8аOH), 3078 br (С8=СOH),
1723 (С6=O), 1698 (C7=O), 1603 br (C1=O in intramo-
lecular hydrogen bond). 1Н NMR spectrum (DMSO-d6),
δ, ppm: 3.90 d.d (2H, C4H2, J 6.5, 4.6 Hz), 4.11 d.d
(2H, C3H2, J 6.5, 4.6 Hz), 7.29 t (1Harom), 7.33 d.d
(2Harom), 7.35 s (1H, С8аOH), 7.39–7.43 m (2Harom),
7.50 t (2Harom), 7.63 t (1Harom), 8.00 d (2H, Ho in
СOPh, J 8.2 Hz). Found, %: C 65.80; H 4.38; N 7.80.
C20H16N2O5. Calculated, %: C 65.93; H 4.43; N 7.69.
radiation at 295(2) K. The structures were solved by
the direct statistical method and refined by full-matrix
least-squares method with respect to F2 in anisotropic
approximation for all nonhydrogen atoms. A part of
hydrogen atoms was placed in geometrically calculated
positions and was included in the refinement in a rider
model with thermal parameters depending on parent
atoms; another part of hydrogen atoms was solved and
refined independently in an isotropic approximation.
All calculations were performed using SHELX 97
software [15].
The analysis of compound 2a (empirical formula
C20H14N2O4) was carried out using colorless crystal of
the size 0.25 × 0.17 × 0.09 mm. Crystal triclinic, space
group Р-1, a 5.9760(6),
b 11.8515(11), c 13.5823(8) Å,
α 100.406(7), β 90.771(7), γ 95.331(8) deg, V
941.60(14) Å3, dcalc 1.222 g/cm3, Z 2. In the angles
range 3.05 < θ < 28.28° 4618 independent reflections
were measured, 1875 with I > 2σ(I). The completeness of
the experiment for the angle θ 28.28° was 99.3%. No
corrections for extinction were introduced (μ 0.087 mm–1).
Final refinement results were as follows: R1 0.0451,
wR2 0.1205 for reflections with I > 2σ(I), R1 0.0968,
wR2 0.1260 (for all reflections), S 1.001. Maximum
and minimum peaks of residual electron density are
0.156 and –0.182 ēÅ–3.
Compounds 3b, 3c were synthesized similarly.
(E)-8a-Hydroxy-8-[hydroxy(phenyl)methyl-
idene]-2-(4-tolyl)tetrahydropyrrolo[1,2-a]pyrazine-
1,6,7(2H)-trione (3b). Yield 93%, mp 149–151°С
(decomp., toluene). IR spectrum, ν, cm–1: 3450–3050
(2OH), 1720 (С6=O), 1698 (С7=O), 1585 br (C1=O in
1
intramolecular hydrogen bond). Н NMR spectrum
(CDCl3), δ, ppm: 2.33 s (3H, Me), 4.02 d.d (2H, C4H2,
J 3.8, 6.6 Hz), 4.10 d.d (2H, C3H2, J 3.8, 6.6 Hz),
7.13–7.24 group of signals (4Harom), 7.31 s (1H, С8аOH),
7.44 t (2Harom), 7.57 t (1Harom), 7.86 d [2H, Ho in С
(OH)Ph, J 8.3 Hz]. Mass spectrum: m/z 379.11 [M +
H]+. Found, %: C 66.72; H 4.68; N 7.31. C21H18N2O5.
Calculated, %: C 66.66; H 4.80; N 7.40. M 379.13.
The analysis of compound 3b (empirical formula
C21H18N2O5·2H2O) was carried out using yellow crystal
of the size 0.60 × 0.40 × 0.40 mm, grown from
the toluene saturated with water. Crystal triclinic,
space group Р-1, a 8.8608(10), b 8.9181(10), c
13.9454(15) Å, α 87.661(9), β 73.676(10), γ 72.816(10)°,
V 1009.28(19) Å3, dcalc 1.364 g/cm3, Z 2. In the angles
range 2.99 < θ < 29.65o 4778 independent reflections
were measured, 3810 with I > 2σ(I). The completeness
of the experiment for the angle θ < 26.00° was 99.6%.
The extinction was accounted for empirically using
the algorithm SCALE3 ABSPACK [16]. Final
refinement results were as follows: R1 0.0474, wR2
0.1218 for reflections with I > 2σ(I), R1 0.0602, wR2
0.1289 for all reflections, S 1.077. Maximum and
minimum peaks of residual electron density are 0.274
and –0.226 ē Å–3.
(E)-8a-Hydroxy-8-[hydroxy(4-chlorophenyl)me-
thylidene]-2-phenyltetrahydropyrrolo[1,2-a]pyrazi-
ne-1,6,7(2H)-trione (3c). Yield 88%, mp 153–155°С
(decomp., toluene). IR spectrum, ν, cm–1: 3185 (С8аOH),
3064 br (С8=СOH), 1693 (С6=O, C7=O), 1597 br (C1=O
1
in intramolecular hydrogen bond). Н NMR spectrum
(CDCl3), δ, ppm: 4.00 d.d (2H, C4H2, J 6.5, 4.2 Hz),
4.10 d.d (2H, C3H2, J 6.5, 4.2 Hz), 7.24–7.41 m (5H,
Ph), 7.38 s (1H, С8аOH), 7.39 d (2H, Hm in C6H4Cl-4,
J 8.4 Hz), 7.77 d (2H, Ho in C6H4Cl-4, J 8.4 Hz).
Found, %: C 60.39; H 3.66; N 6.89. C20H15ClN2O5.
Calculated, %: C 60.24; H 3.79; N 7.02.
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CHERVYAKOV et al.
1592
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in the Cambridge Crystallographic Data Center under
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The study was carried out under the financial
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the Russian Federation (project no. 965), Ministry of
Education of Perm District (MIG competition), and of
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