Activated sterically strained C=N bond in N-substituted p-quinone mono- and diimines: XV. Synthesis, structure, and reactions with alcohols of N-carbamoyl-1,4-benzoquinone imines

Article abstract of DOI:10.1134/S1070428015120131

The reaction of 4-aminophenols with N-nitrourea or with sodium cyanate in acetic acid gave the corresponding 4-ureidophenols which were oxidized to N-carbamoyl-1,4-benzoquinone imines, substituted N-(4-oxocyclohexa-2,5-dien-1-ylidene)ureas. N-(2,6-Dimethy

Full text of DOI:10.1134/S1070428015120131

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2015, Vol. 51, No. 12, pp. 1739–1744. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © S.A. Konovalova, A.P. Avdeenko, M.V. Polishchuk, E.N. Lysenko, V.N. Baumer, I.V. Omel’chenko, S.A. Goncharova, 2015,
published in Zhurnal Organicheskoi Khimii, 2015, Vol. 51, No. 12, pp. 1772–1777.
Activated Sterically Strained C=N Bond
in N-Substituted p-Quinone Mono- and Diimines:
XV.* Synthesis, Structure, and Reactions with Alcohols
of N-Carbamoyl-1,4-benzoquinone Imines
S. A. Konovalovaa, A. P. Avdeenkoa, M. V. Polishchuka, E. N. Lysenkoa, V. N. Baumerb,
I. V. Omel’chenkob, and S. A. Goncharovac
a Donbass State Engineering Academy, ul. Shkadinova 72, Kramatorsk, 84313 Ukraine
e-mail: chimist@dgma.donetsk.ua
b Institute for Single Crystals, National Academy of Sciences of Ukraine, pr. Lenina 60, Kharkiv, 61001 Ukraine
c Sumy State University, ul. Rimskogo-Korsakova 2, Sumy, 40000 Ukraine
Received July 9, 2015
Abstract—The reaction of 4-aminophenols with N-nitrourea or with sodium cyanate in acetic acid gave the
corresponding 4-ureidophenols which were oxidized to N-carbamoyl-1,4-benzoquinone imines, substituted
N-(4-oxocyclohexa-2,5-dien-1-ylidene)ureas. N-(2,6-Dimethyl-4-oxocyclohexa-2,5-dien-1-ylidene)urea
possessing activated sterically strained C=N bond reacted with alcohols to afford N-(1-alkoxy-2,6-dimethyl-4-
oxocyclohexa-2,5-dienyl)ureas.
DOI: 10.1134/S1070428015120131
We previously synthesized N-aryl(alkyl)amino-
carbonyl-1,4-benzoquinone imines [2, 3] and showed
that the presence of an NH group in their molecules
considerably affects their reactivity [3]. The goal of the
present work was to synthesize new N-substituted
1,4-benzoquinone imines containing a carbamoyl
group on the nitrogen atom. The most appropriate
starting compounds for the synthesis of N-carbamoyl-
1,4-benzoquinone imines are N-(4-hydroxyphenyl)-
ureas which can be obtained by reaction of the corre-
sponding aromatic amines with sodium cyanate in
acetic acid [4] or by transamination of urea [5–7] or
nitrourea [8, 9] with various alkyl(aryl)amines. These
reactions are commonly carried out in water [5, 8] or
ethanol [9] in the presence of acetic acid or HCl [5].
The most efficient method of synthesis of N-(4-hy-
droxyphenyl)urea (4a) was the reaction of 4-amino-
phenol (1a) with nitrourea 2 according to the proce-
dure described in [9] (Scheme 1, a). The best way to
synthesize 1-(4-hydroxyphenyl)ureas 4b–4g was the
reaction of 4-aminophenols 1b–1g with sodium
cyanate (3) in acetic acid [4] (Scheme 1, b), which
ensured higher yields and was less laborious. Ureas
4a–4g were readily oxidized with lead(IV) acetate,
Scheme 1.
OH
R1
R1
R1
R4
R2
R3
R4
OH
R2
R4
N
O
a: H2NC(O)NHNO2 (2)
b: NaNCO (3), AcOH
[O]
O
O
H2N
N
H
H2N
R2
NH2
R3
R3
1a–1g
4a–4g
5a–5g
R1 = R2 = R3 = R4 = H (a); R1 = Me, R2 = R3 = R4 = H (b); R1 = R2 = R3 = H, R4 = Me (c); R1 = R4 = Me, R2 = R3 = H (d);
R1 = R3 = Me, R2 = R4 = H (e); R1 = R2 = H, R3 = R4 = Me (f); R1 = R2 = Me, R3 = R4 = H (g).
* For communication XIV, see [1].
1739

KONOVALOVA et al.
1740
manganese(IV) oxide, and silver(I) oxide. However,
the oxidation with Pb(OAc)4 and MnO2 gave yellow
noncrystallizable oily substances which were difficult
to purify, and the desired quinone imines were detected
only by TLC. We succeeded in isolating crystalline
quinone imines 5a–5g only when ureas 4a–4g were
oxidized with Ag2O in chloroform (Scheme 1).
angle is larger than 130° [14, 15]. The C=N bond in
N-acyl analogs becomes sterically strained and activat-
ed when the C=N–X bond angle increases or the C=N
bond is twisted and the quinoid ring loses its planar
structure, which may be estimated by the CCNC
torsion angle and deviations of the C1–C6 atoms from
the quinoid ring plane [1].
The structure of quinone imine 5f was determined
by X-ray analysis (Fig. 1). The C1N1C9 bond angle in
molecule 5f is 129.3(1)°, which is considerably larger
than the average value for many quinone imines (124°)
[16] but slightly smaller than 130°. The corresponding
angle in the molecule of previously reported N-phenyl-
carbamoyl derivative 5h is 126.2(4)° (hereinafter, the
X-ray diffraction data for 5h taken from [2] are used).
1
The H NMR spectra of 4a–4g contained signals
from the NH, NH2, and OH protons at δ 7.20–8.17,
5.56–5.73, and 8.04–9.06 ppm, respectively. Methyl
protons in 4b–4g resonated as singlets at δ 2.03–
2.09 ppm, and signals from the aromatic protons were
located in the region δ 6.42–7.23 ppm. Compounds
1
5a–5g displayed in the H NMR spectra a broadened
singlet at δ 5.24–5.89 due to NH2 protons, methyl
proton signals δ 2.05–2.23 ppm, and signals from
protons in the quinoid ring at δ 6.52–7.26 ppm. In the
1H NMR spectrum of 5f, protons on the quinoid ring
gave rise to a broadened singlet, indicating fast Z,E
isomerization on the NMR time scale.
Me
O
O
Ph
N
N
H
Me
5h
N-Substituted 1,4-benzoquinone imines with sub-
stituents in both ortho positions with respect to the
imino carbon atom are known to readily undergo
nucleophilic addition to the C=N bond [10–13]. It was
presumed that activation of the C=N bond is related
to steric strain in the C=N–X fragment due to the
presence of ortho substituents. We introduced the term
“activated sterically strained C=N bond” and found
that such C=N bond is present in N-arenesulfonyl-1,4-
benzoquinone imines provided that the C=N–X bond
The torsion angle C2C1N1C9 in 5f is –0.96° against
–2.77° in 5h, and the C1–C6 fragment in 5f and 5h may
be regarded as planar with an accuracy of 0.04 and
0.02 Å, respectively, which is typical of quinone
imines having no ortho substituents with respect to the
imino group [1]. The quinoid ring in 5f is less planar
due to cis deformation implying that the C2, C3, C5,
and C6 atoms lie in one plane within 0.01 Å while the
C1 and C4 atoms deviate from that plane by –0.107(2)
and –0.061(2), and O1 and N1, by –0.147(3) and
–0.320(4) Å, respectively. The dihedral angle between
the C1–C6 plane and the urea fragment (N1O2N2C9) is
76.92(5)° in 5f and 87.0(1)° in 5h. The steric strain in
the C=N–C fragment of 5f and 5h can also be judged
by the presence of short intramolecular contacts
C9···C8 {2.91 (5f) and 2.86 Å (5h); the sum of the van
der Waals radii is 3.42 Å [17]} and C9 ···H8C {2.69
(5f) and 2.56 Å (5h); the sum of the van der Waals
radii is 2.87 Å [17]}.
The above data suggest some steric strain in the
C=N–X fragment of molecule 5f; therefore, addition of
alcohols to the C=N bond of 5f may be expected. In
fact, as with other N-substituted 1,4-benzoquinone
imines [1, 2, 10–15], alcohol addition products to the
C=N bond (compounds 7a and 7b) were obtained only
from N-carbamoyl derivative 5f containing methyl
groups in both ortho positions with respect to the
imino carbon atom (Scheme 2). In the 1H NMR spectra
of 7a and 7b we observed a singlet at δ 1.82–1.84 ppm
due to methyl groups in positions 2 and 6, a broadened
C7
C3
C2
O1
N1
C4
C1
C9
O2
C6
C5
N2
C8
Fig. 1. Structure of the molecule of N-(2,6-dimethyl-4-oxo-
cyclohexa-2,5-dien-1-ylidene)urea (5f) according to the
X-ray diffraction data.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 12 2015

ACTIVATED STERICALLY STRAINED C=N BOND ... XV.
singlet at δ 6.10–6.13 ppm due to 3-H and 5-H, and
1741
a broadened singlet from the NH proton at δ 6.76–
6.78 ppm; compound 7a also showed a singlet at
δ 2.89 ppm from the methoxy group.
Scheme 2.
Me
O
AlkO
5f + AlkOH
6a, 6b
O
1 NH
Me
H2N2
7a, 7b
Alk = Me (a), Et (b).
As we showed previously [3], analogous reactions
of N-arylcarbamoyl-1,4-benzoquinone imines with
alcohols afforded not only the corresponding 1,2-ad-
ducts but also cyclization products of the latter,
7a-alkoxy-3-aryl-3a,7-dimethyl-3a,7a-dihydro-1H-
benzimidazole-2,5(3H,4H)-diones. However, we failed
to obtain analogous cyclization products from com-
pounds 7a and 7b. In order to rationalize this differ-
ence we performed quantum chemical calculations of
geometric parameters of compound 7a and 1,2-addi-
tion product 7c reported in [3].
Fig. 2. Structure of the molecule of N-(1-methoxy-2,6-di-
methyl-4-oxocyclohexa-2,5-dien-1-yl)urea (7a) according to
quantum chemical calculations.
EXPERIMENTAL
1
The H NMR spectra were measured on a Varian
VXR-300 spectrometer at 300 MHz relative to TMS.
The IR spectra were recorded in KBr on a UR-20 spec-
trometer. The progress of reactions and the purity of
products were monitored by TLC on Silufol UV-254
plates; samples were applied from solutions in chloro-
form, benzene–hexane (10:1) was used as eluent, and
spots were visualized under UV light.
Me
O
MeO
O
1NH
Me
2 NH
Ph
7c
Quantum chemical calculations were performed
using Gaussian 03 software package [18]. The molec-
ular structures were optimized for the gas phase at the
DFT level with B3LYP functional [19–24] and stan-
dard 6-31+G(d) basis set [25, 26]. Conjugative and
hyperconjugative interactions were included by the
natural bond orbital (NBO) analysis [27] using NBO
5.0 software [28].
The most favorable conformations of molecules 7a
and 7c are characterized by spatial proximity of the
N2H2 (N2H) group and C2=C3 double bond (Fig. 2): the
distance N2···C2 is 3.340 in 7a and 3.068 Å in 7c.
This conformation is favorable for donor–acceptor in-
teraction between the π(C2=C3) and σ*(N2–H) orbitals,
which may be responsible for the subsequent cycliza-
tion. The energy of this interaction in molecule 7c is
15.36 kJ/mol against 2.99 kJ/mol in 7a. The lower
energy for 7a is related to the larger energy gap
between the corresponding orbitals due to considerably
higher energy of the σ*(N2–H) orbital of 7a. The
σ*(N2–H) energy of 7c is reduced due to the presence
of a phenyl substituent on the N2 atom.
The X-ray diffraction data for compound 5f were
obtained from a 0.45×0.25×0.15-mm single crystal
on an Oxford Diffraction diffractometer (MoKα radia-
tion, λ 0.71073 Å, graphite monochromator, Sapphire
3 CCD detector). The structure was solved and refined
using SHELX-97 software package [29]. Monoclinic
crystal system, space group P21/c; C9H10N2O2,
M 178.19 g/mol; unit cell parameters [293(2) K]: a =
4.6965(2), b = 12.2440(5), c = 15.6104(6) Å; β =
96.517(4)°; V = 891.86(6) Å3; Z = 4; dcalc = 1.327 g×
cm–3; F(000) = 376; μ = 0.096 mm–1; transmission
These results suggest that the cyclization of the
alcohol addition products to the C=N bond of N-car-
bamoyl-1,4-benzoquinone imines should be favored by
introduction of an aryl substituent into the CON2H
group to reduce the σ*(N2–H) energy.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 12 2015

KONOVALOVA et al.
1742
N-(4-Hydroxy-2-methylphenyl)urea (4c). Yield
81%, mp 223–225°C. H NMR spectrum (DMSO-d6),
coefficients Tmin/Tmax 0.9581/0.9858; –5 ≤ h ≤ 5, –15 ≤
k ≤ 15, –19 ≤ l ≤ 19; ω-scanning, 3.04 ≤ θ ≤ 25.99°.
Total of 11961 reflection intensities were measured,
1724 of which were independent (Rint = 0.0228), and
1407 reflections were characterized by Ihkl > 2σ(I);
completeness 98.5%. Hydrogen atoms were localized
by difference syntheses, and their positions were
refined according to the riding model, except for the
NH hydrogen atoms which were refined in isotropic
approximation with fixed thermal parameters. The full
matrix refinement against F2 was terminated at RF =
0.0344, wR2 = 0.0972 [reflections with I > 2σ(I)]; RF =
0.0441, wR2 = 0.1040 (all independent reflections);
goodness of fit 0.995; Δρmin/Δρmax –0.118/0.134 ē/Å3.
The coordinate of atoms and complete tables of bond
lengths and bond angles for compound 5f were
deposited to the Cambridge Crystallographic Data
Centre (entry no. CCDC 1025982).
1
δ, ppm: 2.09 s (3H, 2-Me), 5.73 br.s (2H, NH2),
6.51 d.d (1H, 5-H, J = 1.8, 9 Hz), 6.56 d (1H, 3-H, J =
1.8 Hz), 7.23 d (1H, 6-H, J = 9 Hz), 7,47 s (1H, NH),
8.97 br.s (1H, OH). Found, %: N 17.29, 16.27.
C8H10N2O2. Calculated, %: N 16.86.
N-(4-Hydroxy-2,3-dimethylphenyl)urea (4d).
1
Yield 78%, mp 182–183°C. H NMR spectrum
(DMSO-d6), δ, ppm: 2.03 s (3H, 2-Me), 2.04 s (3H,
3-Me), 5.62 br.s (2H, NH2), 6.55 d (1H, 5-H, J =
9 Hz), 6.94 d (1H, 6-H, J = 9 Hz), 7.47 s (1H, NH),
8.98 br.s (1H, OH). Found, %: N 15.12, 15.23.
C9H12N2O2. Calculated, %: N 15.55.
N-(4-Hydroxy-2,5-dimethylphenyl)urea (4e).
1
Yield 85%, mp 223–224°C. H NMR spectrum
(DMSO-d6), δ, ppm: 2.03 s (3H, 2-Me), 2.05 s (3H,
5-Me), 5.68 br.s (2H, NH2), 6.54 d (1H, 3-H, J =
9 Hz), 7.13 d (1H, 6-H, J = 9 Hz), 7.39 s (1H, NH),
8.83 br.s (1H, OH). Found, %: N 15.43, 15.12.
C9H12N2O2. Calculated, %: N 15.55.
N-(4-Hydroxyphenyl)ureas 4a–4g (general proce-
dure). a. N-Nitrourea [30], 1.53 g (14.6 mmol), was
added to a mixture of 12 mmol of aminophenol 1a–1g
and 15–20 mL of water. The mixture was heated for
45–60 min on a water bath in a flask equipped with
a reflux condenser which was connected to a bubble
counter. When gas no longer evolved, the precipitate
was filtered off and recrystallized from water.
N-(4-Hydroxy-2,6-dimethylphenyl)urea (4f).
1
Yield 71%, mp 245–247°C. H NMR spectrum
(DMSO-d6), δ, ppm: 2.06 s (6H, 2-Me, 6-Me),
5.56 br.s (2H, NH2), 6.42 s (2H, 3-H, 5-H), 7.20 s (1H,
NH), 9.06 br.s (1H, OH). Found, %: N 14.84, 15.27.
C9H12N2O2. Calculated, %: N 15.55.
b. A solution of 1 g (15.4 mmol) of sodium cyanate
(3) in 10 mL of water was added under stirring at 20°C
to a solution of 7.7 mmol of aminophenol 1a–1g in
a mixture of 5 mL of glacial acetic acid and 10 mL of
water. The first part of NaOCN solution, 3–4 mL, was
added until a solid separated, and the remaining part
was added under vigorous stirring. The mixture was
then stirred for 10–15 min and left to stand for 2–3 h at
room temperature. The precipitate was filtered off,
washed with water, and dried in air.
N-(4-Hydroxy-3,5-dimethylphenyl)urea (4g).
Yield 64%, mp 190–191°C. H NMR spectrum
(DMSO-d6), δ, ppm: 2.09 s (6H, 3-Me, 5-Me), 5.64 s
(2H, NH2), 6.90 s (2H, 2-H, 6-H), 7.76 s (1H, NH),
8.04 s (1H, OH). Found, %: N 16.47, 16.08.
C9H12N2O2. Calculated, %: N 15.55.
1
N-Carbamoyl-1,4-benzoquinone imines 5a–5g
(general procedure). Silver oxide, 1.54 g (6.8 mmol),
was added to a mixture of 6.2 mmol of N-(4-hydroxy-
phenyl)urea 4a–4g and 30–35 mL of chloroform, and
the mixture was stirred for 1.5 h (4a, 4g) or 2–3 h
(4b–4e). The mixture was then filtered, the filtrate was
evaporated, and the yellow solid was recrystallized
from benzene.
N-(4-Hydroxyphenyl)urea (4a). Yield 50%,
1
mp 171–173°C. H NMR spectrum (DMSO-d6), δ,
ppm: 6.63 d (2H, 2-H, 6-H, J = 9 Hz), 7.15 d (2H, 3-H,
5-H, J = 9 Hz), 5.68 br.s (2H, NH2), 8.17 s (1H, NH),
8.96 br.s (1H, OH). Found, %: N 17.32, 18.10.
C7H8N2O2. Calculated, %: N 18.41.
N-(4-Oxocyclohexa-2,5-dien-1-ylidene)urea (5a).
1
Yield 40%, mp 90–91°C. H NMR spectrum (CDCl3),
δ, ppm: 5.41 br.s (1H, NH2), 5.83 br.s (1H, NH2),
6.61 d.d (1H, 6-H, J = 2.4, 12.9 Hz), 6,70 d.d (1H,
2-H, J = 2.4, 12.9 Hz), 7.10 d.d (1H, 5-H, J = 2.4,
12.9 Hz), 7.26 d.d (1H, 3-H, J = 2.4, 12.9 Hz). Found,
%: N 17.86, 17.69. C7H6N2O2. Calculated, %: N 18.66.
N-(4-Hydroxy-3-methylphenyl)urea (4b). Yield
78%, mp 194–195°C. H NMR spectrum (DMSO-d6),
1
δ, ppm: 2.07 s (3H, 3-Me), 5.67 br.s (2H, NH2), 6.63 d
(1H, 5-H, J = 9 Hz), 6.97 d.d (1H, 6-H, J = 1.8,
9.0 Hz), 7.06 d (1H, 2-H, J = 1.8 Hz), 8.11 s (1H, NH),
8.83 br.s (1H, OH). Found, %: N 17.25, 15.86.
C8H10N2O2. Calculated, %: N 16.86.
N-(3-Methyl-4-oxocyclohexa-2,5-dien-1-ylidene)-
urea (5b). Yield 45%, mp 121–122°C. 1H NMR spec-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 12 2015

ACTIVATED STERICALLY STRAINED C=N BOND ... XV.
1743
trum (CDCl3), δ, ppm: Z isomer (60%): 2.05 br.s (3H,
3-Me), 5.41 br.s and 5.89 br.s (1H each, NH2), 6.67 d
(1H, 5-H, J = 9.3 Hz), 7.03 d.d (1H, 6-H, J = 2.1,
9.3 Hz), 7.05 br.s (1H, 2-H); E isomer (40%): 2.07 br.s
(3H, 3-Me), 5.41 br.s and 5.89 br.s (1H each, NH2),
6.58 d (1H, 5-H, J = 9.3 Hz), 6.90 br.s (1H, 2-H),
7.20 d.d (1H, 6-H, J = 2.1, 9.3 Hz). Found, %:
N 17.64, 16.35. C8H8N2O2. Calculated, %: N 17.06.
N-(1-Methoxy-2,6-dimethyl-4-oxocyclohexa-2,5-
dien-1-yl)urea (7a). Yield 43%, mp 185–186°C.
1H NMR spectrum (DMSO-d6), δ, ppm: 1.82 br.s (6H,
2-Me, 6-Me), 2.89 br.s (3H, MeO), 5.62 br.s (2H,
NH2), 6.13 br.s (2H, 3-H, 5-H), 6.76 br.s (1H, NH).
Found, %: N 14.86, 15.04. C8H10N2O3. Calculated, %:
N 15.39.
N-(1-Ethoxy-2,6-dimethyl-4-oxocyclohexa-2,5-
dien-1-yl)urea (7b). Yield 55%, mp 156–157°C.
1H NMR spectrum (DMSO-d6), δ, ppm: 1.07–1.11 t
(3H, CH2CH3), 1.84 br.s (6H, 2-Me, 6-Me), 3.01–
3.05 d.d (2H, CH2CH3), 5.58 br.s (2H, NH2), 6.10 br.s
(2H, 3-H, 5-H), 6.78 br.s (1H, NH). Found, %:
N 12.05, 12.34. C11H16N2O3. Calculated, %: N 12.49.
N-(2-Methyl-4-oxocyclohexa-2,5-dien-1-ylidene)-
1
urea (5c). Yield 42%, mp 137–138°C. H NMR spec-
trum (CDCl3), δ, ppm: 2.18 d (3H, 2-Me, J = 1.5 Hz),
5.32 br.s and 5.73 br.s (1H each, NH2), 6.53 d.d (1H,
5-H, J = 2.1, 9.3 Hz), 6.54 br.s (1H, 3-H), 7.18 d (1H,
6-H, J = 9.3 Hz). Found, %: N 16.49, 16.71.
C8H8N2O2. Calculated, %: N 17.06.
REFERENCES
N-(2,3-Dimethyl-4-oxocyclohexa-2,5-dien-1-
ylidene)urea (5d). Yield 40%, mp 129–130°C.
1H NMR spectrum (CDCl3), δ, ppm: 2.05 s (3H,
2-Me), 2.16 s (3H, 3-Me), 5.24 br.s and 5.45 br.s
(1H each, NH2), 6.53 d (1H, 5-H, J = 9 Hz), 7.13 d
(1H, 6-H, J = 9 Hz). Found, %: N 15.57, 15.61.
C9H10N2O2. Calculated, %: N 15.72.
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N-(2,5-Dimethyl-4-oxocyclohexa-2,5-dien-1-
ylidene)urea (5e). Yield 55%, mp 159–160°C.
1H NMR spectrum (CDCl3), δ, ppm: 2.01 d (3H, 2-Me,
J = 1.8 Hz), 2.15 d (3H, 5-Me, J = 1.8 Hz), 5.32 br.s
and 5.81 br.s (1H each, NH2), 6.52 s (1H, 3-H), 6.97 s
(1H, 6-H). Found, %: N 15.23, 15.42. C9H10N2O2. Cal-
culated, %: N 15.72.
1922, vol. 44, p. 2595.
7. Hjort, A.M., DeBeer, E.J., Buck, J.S., and Ide, W.S.,
J. Pharm. Pharmacol., 1935, vol. 66, p. 152.
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6-Me), 5.54 br.s (2H, NH2), 6.40 br.s (2H, 3-H, 5-H).
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