Reaction of 1-aryl-3-(4,4-diethoxybutyl)ureas with phenols. Synthesis of 2-arylpyrrolidines

Article abstract of DOI:10.1134/S1070428014120161

Acid-catalyzed reaction of phenols with 1-(4,4-diethoxybutyl)urea derivatives gave new 2-arylpyrrolidines containing 4-bromoresorcinol and hydroquinone fragments. The described reaction is advantageous due to its mild conditions and no necessity of using

Full text of DOI:10.1134/S1070428014120161

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2014, Vol. 50, No. 12, pp. 1809–1813. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © A.S. Gazizov, A.V. Smolobochkin, A.R. Burilov, M.A. Pudovik, 2014, published in Zhurnal Organicheskoi Khimii, 2014, Vol. 50,
No. 12, pp. 1828–1831.
Reaction of 1-Aryl-3-(4,4-diethoxybutyl)ureas with Phenols.
Synthesis of 2-Arylpyrrolidines
A. S. Gazizova, A. V. Smolobochkinb, A. R. Burilova, and M. A. Pudovika
a Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences,
ul. Arbuzova 8, Kazan, 420088 Tatarstan, Russia
e-mail: agazizov@iopc.ru
b Kazan National Research Technological University, ul. Karla Marksa 68, Kazan, 420015 Tatarstan, Russia
Received June 14, 2014
Abstract—Acid-catalyzed reaction of phenols with 1-(4,4-diethoxybutyl)urea derivatives gave new 2-arylpyr-
rolidines containing 4-bromoresorcinol and hydroquinone fragments. The described reaction is advantageous
due to its mild conditions and no necessity of using expensive or toxic catalyst.
DOI: 10.1134/S1070428014120161
2-Arylpyrrolidines constitute an important class of
heterocycles widely represented by both biologically
active natural compounds and their synthetic analogs
[1–3]. Known methods of synthesis of 2-arylpyrroli-
dines are based on two main approaches. The first of
these implies modification of pyrrolidine ring already
obtained in one or another way, and the second in-
volves intra- or intermolecular cyclization with forma-
tion of pyrrolidine ring, where the aryl fragment is
either included into the precursor molecule or intro-
duced directly at the stage of formation of pyrrolidine
ring [4–6]. The existing methods are generally multi-
step, and they require harsh conditions and toxic or
expensive catalysts.
rolidines in good yields. Important advantages of the
proposed approach are mild reaction conditions and
the use of accessible trifluoroacetic acid as catalyst.
It was interesting to elucidate whether less reactive
phenols, in particular 4-bromoresorcinol and hydro-
quinone, could be involved in analogous reaction.
Initial ureido acetals IIa–IId were synthesized as
shown in Scheme 1. 1-(4,4-Diethoxybutyl)-3-phenyl-
urea (IIa) was prepared by reaction of 4,4-diethoxy-
butan-1-amine with phenyl isocyanate. Acetals IIb–IId
were obtained from the corresponding aromatic amines
and 1,1′-carbonyldiimidazole (CDI) with subsequent
treatment of the resulting N-aryl-1H-imidazole-1-car-
boxamides with γ-amino acetal I [7].
We previously studied reactions of 1-(4,4-diethoxy-
butyl)urea derivatives (γ-ureido acetals) with some
phenols, such as resorcinol, 2-methylresorcinol, and
pyrogallol [7]. These reactions produced 2-arylpyr-
Acetals IIa–IId reacted with an equimolar amount
of 4-bromoresorcinol in chloroform in the presence of
1 equiv of trifluoroacetic acid to give 2-arylpyrroli-
dines IIIa–IIId (Scheme 2). Likewise, the reaction of
Scheme 1.
OEt
OEt
H
H
PhNCO
N
N
NH2
EtO
Ph
EtO
O
I
IIa
OEt
H
H
H
CDI, CH2Cl2, 45°C, 12 h
I, CHCl3, 20°C, 20 h
N
N
N
R
N
N
RNH2
EtO
R
O
O
IIb–IId
CDI is 1,1′-carbonyldiimidazole; R = 4-MeOC6H4 (b), 4-BrC6H4 (c), 4-O2NC6H4 (d).
1809

GAZIZOV et al.
1810
Scheme 2.
OH
Br
OH
Br
IIa–IId, CF3COOH
CHCl3, 20°C, 20 h
N
NHR
HO
HO
O
IIIa–IIId
R = Ph (a), 4-MeOC6H4 (b), 4-BrC6H4 (c), 4-O2NC6H4 (d).
Scheme 3.
HO
O
RNH
CF3COOH, CHCl3
OH
20°C, 120 h
N
+
2IIa–IId
HO
NHR
O
OH
IVa–IVd
R = Ph (a), 4-MeOC6H4 (b), 4-BrC6H4 (c), 4-O2NC6H4 (d).
IIa–IId with hydroquinone at a ratio of 2:1 afforded
phenylenedipyrrolidines IVa–IVd via substitution at
the 2,5-positions of hydroquinone (Scheme 3). Among
the examined phenols, hydroquinone turned out to be
the least reactive, and target heterocyclic compounds
IVa–IVd were isolated in poor yields after prolonged
keeping of the reaction mixtures at room temperature.
A probable reason is inconsistent effect of the hydroxy
groups.
rationalize the observed difference in the stereo-
chemical behavior of acetals IIa–IId in the reaction
with hydroquinone. Unfortunately, we failed to isolate
pure diastereoisomers of IVa, IVc, and IVd because of
their very poor solubility in most solvents and small
difference in the Rf values (<0.15).
It seemed also reasonable to synthesize compounds
containing two pyrrolidine fragments on the basis of
4-bromoresorcinol. For this purpose, γ-amino acetal I
was brought into reaction with hexamethylene and
p-phenylene diisocyanates at a ratio of 2:1 to obtain
bis-acetals Va and Vb [7] (Scheme 4). The reaction of
Va and Vb with 2 equiv of 4-bromoresorcinol in
According to the NMR data, compounds IVa, IVc,
and IVd were formed as mixtures of two diastereo-
isomers at a ratio of ~2:1. Compound IVb was isolat-
ed as a single diastereoisomer. It is now difficult to
Scheme 4.
OEt
OEt
OEt
H
H
H
H
OCN–X–NCO
N
N
N
N
2I
EtO
X
O
O
Va, Vb
X = (CH2)6 (a), 1,4-C6H4 (b).
Scheme 5.
H
H
OH
Br
N
N
N
N
X
Va, Vb, CF3COOH
CHCl3, 20°C, 72 h
HO
OH
O
O
2
HO
Br
Br
HO
OH
VIa, VIb
X = (CH2)6 (a), 1,4-C6H4 (b).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 12 2014

REACTION OF 1-ARYL-3-(4,4-DIETHOXYBUTYL)UREAS WITH PHENOLS.
1811
chloroform in the presence of trifluoroacetic acid led to
the formation of desired compounds VIa and VIb
containing two pyrrolidine rings (Scheme 5). Com-
pounds VIa and VIb could also be formed as mixtures
of diastereoisomers. However, only one set of signals
was observed in their NMR spectra, which may be due
to both high diastereoselectivity of the reaction and
very small difference in the chemical shifts of the
respective nuclei in the two diastereoisomers. This
problem requires further investigation.
Mass spectrum: m/z 377 [M + H]+. Found, %: C 54.41;
H 4.42; Br 20.88; N 7.67. C17H17BrN2O3. Calculated,
%: C 54.13; H 4.54; Br 21.18; N 7.43. M 377.24.
Compounds IIIb–IIId were synthesized in a simi-
lar way.
2-(5-Bromo-2,4-dihydroxyphenyl)-N-(4-methoxy-
phenyl)pyrrolidine-1-carboxamide (IIIb) was syn-
thesized from 0.25 g (0.81 mmol) of 1-(4,4-diethoxy-
butyl)-3-(4-methoxyphenyl)urea and 0.15 g
(0.81 mmol) of 4-bromoresorcinol in the presence of
0.09 g (0.81 mmol) of trifluoroacetic acid in 5 mL of
anhydrous chloroform. Yield 0.24 g (73%), mp 218–
219°C. IR spectrum, ν, cm–1: 3281 (O–H), 2983, 2876
The reactions of hydroquinone with acetals Va and
Vb led to the formation of complex mixtures of prod-
ucts which we failed to isolate and identify.
1
(N–H), 1632 (C=O), 1597 (C=Carom). H NMR spec-
In summary, we have synthesized new 2-arylpyr-
rolidine derivatives by reactions of 4-bromoresorcinol
and hydroquinone with γ-ureido acetals. The described
procedure is advantageous due to mild reaction condi-
tions and the use of accessible inexpensive reactants.
trum, δ, ppm: 1.70–1.82 m (2H, CH2), 1.84–1.93 m
(1H, CH2), 2.07–2.19 m (1H, CH2), 3.42–3.51 m and
3.68–3.75 m (1H each, NCH2), 3.69 s (3H, OMe),
5.08–5.13 m (1H, CHN), 6.51 s (1H, Harom), 6.80 d
(2H, Harom, J = 9.05 Hz), 6.91 s (1H, Harom), 7.33 d
(2H, Harom, J = 9.05 Hz). Mass spectrum: m/z 431
[M + Na]+. Found, %: C 53.25; H 4.51; Br 19.39;
N 7.01. C18H19BrN2O4. Calculated, %: C 53.08;
H 4.70; Br 19.62; N 6.88. M 407.26.
EXPERIMENTAL
1
The H and 13C NMR spectra were recorded on
Bruker MSL 400 (400 MHz) and Bruker Avance 600
(150 MHz) spectrometers, respectively, from solutions
in DMSO-d6; the chemical shifts were determined
relative to the residual proton and carbon signals of the
deuterated solvent. The IR spectra were measured in
KBr on a UR-20 spectrometer. The mass spectra
(MALDI-TOF) were obtained on a Bruker Ultraflex III
instrument using plastic and metal targets and 2,5-di-
hydroxybenzoic acid as matrix. The melting points
were determined in glass capillaries on a Stuart SMP
10 melting point apparatus.
2-(5-Bromo-2,4-dihydroxyphenyl)-N-(4-bromo-
phenyl)pyrrolidine-1-carboxamide (IIIc) was syn-
thesized from 0.25 g (0.70 mmol) of 1-(4-bromo-
phenyl)-3-(4,4-diethoxybutyl)urea and 0.13 g
(0.70 mmol) of 4-bromoresorcinol in the presence of
0.08 g (0.70 mmol) of trifluoroacetic acid in 5 mL of
anhydrous chloroform. Yield 0.22 g (70%), mp 136–
137°C. IR spectrum, ν, cm–1: 3395 (O–H), 2976, 2863
1
(N–H), 1641 (C=O), 1592 (C=Carom). H NMR spec-
trum, δ, ppm: 1.66–1.79 m (2H, CH2), 1.80–1.89 m
(1H, CH2), 2.03–2.14 m (1H, CH2), 3.40–3.48 m and
3.66–3.74 m (1H each, NCH2), 5.05–5.10 m (1H,
CHN), 6.47 s (1H, Harom), 6.84 s (1H, Harom), 7.33 d
(2H, Harom, J = 8.92 Hz), 7.40 d (2H, Harom, J =
8.92 Hz). 13C NMR spectrum, δC, ppm: 23.56, 32.85,
47.14, 55.60, 98.25, 104.17, 113.47, 121.62, 123.51,
129.33, 131.45, 140.40, 153.44, 153.92, 154.49. Mass
spectrum: m/z 456 [M]+. Found, %: C 44.65; H 3.71;
Br 34.83; N 6.42. C17H16Br2N2O3. Calculated, %:
C 44.76; H 3.54; Br 35.04; N 6.14. M 456.13.
2-(5-Bromo-2,4-dihydroxyphenyl)-N-phenylpyr-
rolidine-1-carboxamide (IIIa). To a solution of 0.50 g
(1.79 mmol) of 1-(4,4-diethoxybutyl)-3-phenylurea in
10 mL of anhydrous chloroform we added 0.34 g
(1.79 mmol) of 4-bromoresorcinol and 0.20 g
(1.79 mmol) of trifluoroacetic acid. The mixture was
stirred for 3 days at room temperature, and the precip-
itate was filtered off, washed with chloroform, and
dried for 2 h under reduced pressure (0.01 mm). Yield
0.19 g (28%), mp 153–154°C. IR spectrum, ν, cm–1:
3419 (O–H), 2938, 2827 (N–H), 1639 (C=O), 1596
2-(5-Bromo-2,4-dihydroxyphenyl)-N-(4-nitro-
phenyl)pyrrolidine-1-carboxamide (IIId) was syn-
thesized from 0.10 g (0.31 mmol) of 1-(4,4-diethoxy-
butyl)-3-(4-nitrophenyl)urea and 0.06 g (0.31 mmol)
of 4-bromoresorcinol in the presence of 0.04 g
(0.31 mmol) of trifluoroacetic acid in 5 mL of anhy-
drous chloroform. Yield 0.07 g (57%), mp 139–140°C.
1
(C=Carom). H NMR spectrum, δ, ppm: 1.66–1.79 m
(2H, CH2), 1.80–1.89 m (1H, CH2), 2.04–2.15 m (1H,
CH2), 3.41–3.49 m and 3.68–3.75 m (1H each, NCH2),
5.06–5.11 m (1H, CHN), 6.47 s (1H, Harom), 6.86 t (1H,
Harom, J = 7.39 Hz), 6.87 s (1H, Harom), 7.16 t (2H,
Harom, J = 8.19 Hz), 7.40 d (2H, Harom, J = 7.60 Hz).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 12 2014

GAZIZOV et al.
1812
IR spectrum, ν, cm–1: 3437, 3398 (O–H), 2945, 2869
(N–H), 1639 (C=O), 1595 (C=Carom). H NMR spec-
2,2′-(2,5-Dihydroxybenzene-1,4-diyl)bis-
[N-(4-bromophenyl)pyrrolidine-1-carboxamide]
(IVc) was synthesized from 0.25 g (0.69 mmol) of
1-(4-bromophenyl)-3-(4,4-diethoxybutyl)urea and
0.04 g (0.35 mmol) of hydroquinone in the presence of
0.08 g (0.69 mmol) of trifluoroacetic acid in 5 mL
of anhydrous chloroform. Yield 0.05 g (21%),
mp >250°C. IR spectrum, ν, cm–1: 3266 (O–H), 2864,
1
trum, δ, ppm: 1.66–1.79 m (2H, CH2), 1.80–1.89 m
(1H, CH2), 2.06–2.17 m (1H, CH2), 3.45–3.55 m and
3.73–3.80 m (1H each, NCH2), 5.09–5.15 m (1H,
CHN), 6.47 s (1H, Harom), 6.85 s (1H, Harom), 7.69 d
(2H, Harom, J = 9.29 Hz), 8.08 d (2H, Harom, J =
9.29 Hz). Mass spectrum: m/z 422 [M]+. Found, %:
C 48.61; H 3.68; Br 18.62; N 9.72. C17H16BrN3O5.
Calculated, %: C 48.36; H 3.82; Br 18.92; N 9.95.
M 422.24.
1
2878 (N–H), 1651 (C=O), 1588 (C=Carom). H NMR
spectrum, δ, ppm: 1.73–1.86 m (4H, CH2), 1.87–
1.97 m (2H, CH2), 2.08–2.24 m (2H, CH2), 3.49–
3.59 m (2H, NCH2), 3.65–3.76 m (2H, NCH2), 5.15–
5.22 m (2H, CHN), 6.46 s (1.4H, Harom), 6.48 s (0.6H,
2,2′-(2,5-Dihydroxybenzene-1,4-diyl)bis(N-phe-
nylpyrrolidine-1-carboxamide) (IVa). To a solution
of 0.50 g (1.79 mmol) of 1-(4,4-diethoxybutyl)-3-
phenylurea in 10 mL of anhydrous chloroform we
added 0.10 g (0.89 mmol) of hydroquinone and 0.10 g
(0.89 mmol) of trifluoroacetic acid, and the mixture
was stirred for 5 days at room temperature. The precip-
itate was filtered off, washed with ethanol (10 mL),
and dried for 2 h under reduced pressure (0.01 mm).
Yield 0.13 g (30%), mp >250°C. IR spectrum, ν, cm–1:
3437, 3398 (O–H), 2869, 2727 (N–H), 1645 (C=O),
H
H
arom), 7.32–7.41 m (4H, Harom), 7.42–7.53 m (4H,
arom). Mass spectrum: m/z 667 [M + Na]+. Found, %:
C 52.73; H 4.65; Br 24.58; N 8.84. C28H28Br2N4O4.
Calculated, %: C 52.91; H 4.38; Br 24.80; N 8.70.
M 644.36.
2,2′-(2,5-Dihydroxybenzene-1,4-diyl)bis[N-(4-ni-
trophenyl)pyrrolidine-1-carboxamide] (IVd) was
synthesized from 0.10 g (0.31 mmol) of 1-(4,4-di-
ethoxybutyl)-3-(4-nitrophenyl)urea and 0.02 g
(0.16 mmol) of hydroquinone in the presence of 0.04 g
(0.31 mmol) of trifluoroacetic acid in 5 mL of anhy-
drous chloroform. Yield 0.02 g (19%), mp >250°C. IR
spectrum, ν, cm–1: 3343 (O–H), 2921, 2876 (N–H),
1668 (C=O), 1597 (C=Carom), 1558, 1333 (NO2).
1H NMR spectrum, δ, ppm: 1.75–1.87 m (4H, CH2),
1.88–1.97 m (2H, CH2), 2.11–2.22 m (2H, CH2), 3.54–
3.66 m (2H, NCH2), 3.71–3.81 m (2H, NCH2), 5.19–
5.22 m (2H, CHN), 6.45 s (1.4H, Harom), 6.47 s (0.6H,
1
1595 (C=Carom). H NMR spectrum, δ, ppm: 1.74–
1.86 m (4H, CH2), 1.87–1.96 m (2H, CH2), 2.11–
2.24 m (2H, CH2), 3.49–3.60 m (2H, NCH2), 3.65–
3.76 m (2H, NCH2), 5.12–5.19 m (2H, CHN), 6.48 s
(0.7H, Harom), 6.51 s (1.3H, Harom), 6.86–6.95 m (2H,
Harom), 7.16–7.24 m (4H, Harom), 7.41–7.50 m (4H,
Harom). Mass spectrum: m/z 509 [M + Na]+. Found, %:
C 68.99; H 6.42; N 11.77; C28H30N4O4. Calculated, %:
C 69.12; H 6.21; N 11.51. M 486.57.
H
H
arom), 7.72–7.83 m (4H, Harom), 8.08–8.17 m (4H,
arom). Mass spectrum: m/z 599 [M + Na]+. Found, %:
Compounds IVb–IVd were synthesized in a similar
way.
C 58.19; H 5.14; N 14.29. C28H28N6O8. Calculated, %:
C 58.33; H 4.89; N 14.58. M 576.57.
2,2′-(2,5-Dihydroxybenzene-1,4-diyl)bis-
[N-(4-methoxyphenyl)pyrrolidine-1-carboxamide]
(IVb) was obtained from 0.30 g (0.97 mmol) of
1-(4,4-diethoxybutyl)-3-(4-methoxyphenyl)urea and
0.05 g (0.48 mmol) of hydroquinone in the presence of
0.11 g (0.97 mmol) of trifluoroacetic acid in 10 mL
of anhydrous chloroform. Yield 0.03 g (12%),
mp >250°C. IR spectrum, ν, cm–1: 3386, 3199 (O–H),
2953, 2888, 2834 (N–H), 1646 (C=O), 1598 (C=Carom).
1H NMR spectrum, δ, ppm: 1.69–1.80 m (4H, CH2),
1.81–1.91 m (2H, CH2), 2.03–2.17 m (2H, CH2), 3.42–
3.51 m (2H, NCH2), 3.61–3.70 m (2H, NCH2), 3.65 s
(6H, OCH3), 5.06–5.14 m (2H, CHN), 6.43 s (2H,
Harom), 6.75 d (4H, Harom, J = 8.56 Hz), 7.30 d (4H,
Harom, J = 8.40 Hz). Mass spectrum: m/z 569 [M + Na]+.
Found, %: C 65.67; H 6.57; N 10.05. C30H34N4O6. Cal-
culated, %: C 65.92; H 6.27; N 10.25. M 546.62.
N,N′-(Hexane-1,6-diyl)bis[2-(5-bromo-2,4-dihy-
droxyphenyl)pyrrolidine-1-carboxamide] (VIa). To
a solution of 0.39 g (0.80 mmol) of 1,1′-(hexane-1,6-
diyl)bis[3-(4,4-diethoxybutyl)urea] in 10 mL of anhy-
drous chloroform we added 0.30 g (1.60 mmol) of
4-bromoresorcinol and 0.08 g (0.70 mmol) of trifluoro-
acetic acid, and the mixture was stirred for 3 days at
room temperature. The precipitate was filtered off,
washed with ethanol (10 mL), and dried for 2 h under
reduced pressure (0.01 mm). Yield 0.11 g (21%),
mp 136–137°C. IR spectrum, ν, cm–1: 3197 (O–H),
2916, 2726 (N–H), 1672 (C=O). 1H NMR spectrum, δ,
ppm: 1.09–1.18 m (4H, CH2), 1.26–1.36 m (4H, CH2),
1.67–1.73 m (4H, CH2), 1.74–1.83 m (2H, CH2), 1.98–
2.10 m (2H, CH2), 2.85–3.03 m (4H, CH2), 3.22–
3.32 m (2H, NCH2), 3.42–3.52 m (2H, NCH2), 4.88–
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 12 2014

REACTION OF 1-ARYL-3-(4,4-DIETHOXYBUTYL)UREAS WITH PHENOLS.
1813
4.92 m (2H, CHN), 5.84 br.s (2H, NH), 6.46 s (2H,
Harom), 6.80 s (2H, Harom). Mass spectrum: m/z 707
[M + Na]+. Found, %: C 48.95; H 5.44; Br 23.05;
N 8.43. C28H36Br2N4O6. Calculated, %: C 49.14;
H 5.30; Br 23.35; N 8.19. M 684.43.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
nos. 14-03-00191-a, 14-03-31740 mol_a).
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N,N′-(Benzene-1,4-diyl)bis[(5-bromo-2,4-dihy-
droxyphenyl)pyrrolidine-1-carboxamide] (VIb) was
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of 1,1′-(benzene-1,4-diyl)bis[3-(4,4-diethoxybutyl)-
urea] and 0.23 g (1.24 mmol) of 4-bromoresorcinol in
the presence of 0.07 g (0.62 mmol) of trifluoroacetic
acid. Yield 0.39 g (92%), mp 213–214°C. IR spectrum,
ν, cm–1: 3404 (O–H), 2896, 2826 (N–H), 1638 (C=O),
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1
1593 (C=Carom). H NMR spectrum, δ, ppm: 1.67–
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1.80 m (4H, CH2), 1.81–90 m (2H, CH2), 2.04–2.17 m
(2H, CH2), 3.34–3.48 m (2H, NCH2), 3.65–3.74 m
(2H, NCH2), 5.06–5.11 m (2H, CHN), 6.49 s (2H,
Harom), 6.88 s (2H, Harom), 7.25 br.s (4H, Harom). Mass
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 12 2014