Transformation of 4-substituted tetrahydro-pyrrolobenzodiazepines in a three-component reaction with methyl propiolate and indole

Article abstract of DOI:10.1007/s10593-014-1431-5

The three-component reaction of 4-phenyl-, p-methoxyphenyl-, and thienylpyrrolo[1,2-a][1,4]benzo-diazepines with methyl propiolate and indole in dichloromethane proceeds through opening of the diazepine ring. The major transformation products isolated are substituted pyrroles, namely, 1-(2-aminomethylphenyl)-5-(arylmethyl)-2-(indol-1(3)-yl)pyrroles and 1-(2-aminomethylphenyl)-2-aryl-(indol-3-yl)-methylpyrroles.

Full text of DOI:10.1007/s10593-014-1431-5

Chemistry of Heterocyclic Compounds, Vol. 49, No. 12, March, 2014 (Russian Original Vol. 49, No. 12, December, 2013)
TRANSFORMATION OF 4-SUBSTITUTED TETRAHYDRO-
PYRROLOBENZODIAZEPINES IN A THREE-COMPONENT
REACTION WITH METHYL PROPIOLATE AND INDOLE
L. G. Voskressensky1*, T. N. Borisova1, M. I. Babakhanova1,
A. A. Titov1, T. M. Chervyakova1, R. A. Novikov2, A. V. Butin3,
V. N. Khrustalev4, and A. V. Varlamov1
The three-component reaction of 4-phenyl-, p-methoxyphenyl-, and thienylpyrrolo[1,2-a][1,4]benzo-
diazepines with methyl propiolate and indole in dichloromethane proceeds through opening of the
diazepine ring. The major transformation products isolated are substituted pyrroles, namely,
1-(2-aminomethylphenyl)-5-(arylmethyl)-2-(indol-1(3)-yl)pyrroles and 1-(2-aminomethylphenyl)-2-aryl-
(indol-3-yl)-methylpyrroles.
Keywords: pyrrolylindoles, tetrahydropyrrolo[1,2-a][1,4]benzodiazepines, domino reactions, multi-
component reaction, opening of the diazepine ring.
The domino reaction of [c]-condensed tetrahydropyridines 1 with alkynes discovered in our previous
work [1-3] has led to the development of methods for the synthesis of condensed azocines 2 and methoxymethyl
derivatives of heterocyclic compounds.
The nucleophilic attack of the anionic site of the initial ammonium zwitter-ion A at the C-1 atom as the
result of expansion of the tetrahydropyridine ring leads to condensed azocines 2, whose ring cleavage by a
methanol molecule gives methoxymethyl derivative 3. Electron-donor substituents R in the methine group
facilitate cleavage of the aryl- or hetarylmethylammonium fragment at the –N+CHR– bond and formation of
zwitterion B, which opens a new transformation pathway, namely, to spiro compounds 4 [4]. The existence of
the open zwitterion was demonstrated using the three-component reaction of benzothienopyridine and -carbo-
line with methyl propiolate and indole. The corresponding triarylmethanes 5 were obtained in 76-85% yield
[5, 6].
_______
*To whom correspondence should be addressed, e-mail: lvoskressensky@sci.pfu.edu.ru.
1Peoples' Friendship University of Russia, 6 Miklukho-Maklaya St., Moscow 117198, Russia.
2N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky Ave., Moscow
119991, Russia; e-mail: novikofff@bk.ru.
3Perm State National Research University, 15 Bukirev St., Perm 614990, Russia; e-mail: alexander_butin@mail.ru.
4A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilova St.,
Moscow 119991, Russia; e-mail: vkh@xray.incos.ac.ru.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1925-1935, December, 2013.
Original article submitted October 17, 2013.
0009-3122/14/4912-1785©2014 Springer Science+Business Media New York
1785

Y
R
Y
R
R
R
Me
N+
Me
X
X
N
X
N
–
Me
Y
1
A
2
MeOH
R
Y
X
R
OMe
N
Y
X
+
–
Indole
N
H
Me
3
N
Me
R
X
N
Me
B
X
Y
5
N
Y
Me
2
4
Condensed azepines and 1,4-diazepines demonstrate unique behavior in domino reactions with alkynes.
While the azepine ring in the tetrahydroindoloazepines readily expands by two carbon atoms by the action of
alkynes to give indoloazonines [7], the diazepine ring in benzodiazepines does not undergo any transformation
by the action of alkynes [8]. Tetrahydrobenzodiazepinones react with alkynes through multiple pathways to give
a multicomponent mixtures, from which Stevens rearrangement products of C- and N-vinylation are separated
by chromatography [8].
Pyrrolo[1,2-a][1,4]benzodiazepines 6 react with methyl propiolate in dichloromethane to give multi-
component mixtures, from which products of the expansion of the diazepine ring at the C(4)–N bond, namely,
pyrrolobenzodiazonines 7 were isolated [9]. In this case, products of the transformation of the diazepine
fragment at the N–C(6) bond were not isolated.
R
R
N Me
R1
CO2Me
CO2Me
R1
N
HC
N
CH2Cl2
N
Me
6
7
R = Ph, 2-thienyl, Ме; R1 = H, Me
In order to confirm the cleavage of the diazepine ring in benzodiazepines 6 in domino reactions with
alkynes and obtain new pyrrolylindolylmethane derivatives 5 holding biological interest, we studied the
transformation of 4-aryl-5-methyldihydropyrrolobenzodiazepines 10a-d by the action of methyl propiolate in
three-component reactions with indole. The synthesis of benzodiazepines 10a-d was carried out according to the
procedure described in our previous work [9] from the corresponding pyrrolobenzylamides 8a-d.
Pyrrolobenzodiazepines 10a,b were described in the same work [9].
Multicomponent mixtures were obtained in three-component reactions of pyrrolobenzodiazepines 10a-c
with methyl propiolate and indole. Only products of opening of the diazepine ring at the C(4)–N bond were
obtained chromatographically in 8.4-28.3% yield, namely, substituted N-arylpyrroles 11a-c, 12a-c, and 13a,b.
Pyrrole 13c was not isolated from the reaction mixture.
1786

1) MeI, acetone
MW (50 W)
R
R
POCl3
150°С, 30 min;
O
N
N
N
N
N Me
2) NaBH4, MeOH
EtOH, H2O
20°С, 10 min
MeCN
, 3 h
N
H
R
8a–d
9a–d
10a–d
a R = Ph, b R = 2-thienyl, c R = 4-МеOC6H4, d R = 4-O2NC6H4
Products of the alternative cleavage at the C(6)–N bond could not be detected. In our opinion, pyrroles
12a-c are the most unusual of the isolated pyrroles. These products may be seen as products of formal
nucleophilic substitution at the -position of the pyrrole ring. Similar formal nucleophilic substitution in
pyrroles using N-halosuccinimides was described by De Rosa et al. [10], who proposed that this reaction
proceeds through 2,5-addition of the haloimides to the pyrrole ring.
CH2Cl2, 35°C
10a–c
HC
CO2Me
+
+
N
H
NH
NH
N
R
R
N
N
N
R
+
+
Me
Me
Me
N
N
N
CO2Me
CO2Me
R
CO2Me
13a–c
11a–c
12a–c
Pyrrolobenzo-
diazepine
Pyrrole yield, %
12
Total yield
11
13
Ph
2-Thienyl
4-МеOC6H4
1.6
18.3
4.8
10.5
4.0
3.6
2.0
6.0
—
14.1
28.3
8.4
10a
10b
10c
The mechanism for formation of pyrroles 11-13 is given in the scheme below. The initially-formed
ammonium zwitterion A deprotonates the indole nitrogen atom by means of its anionic site and undergoes
cleavage to give the open form B. This cation is more stable than the alternative form, which might have been
formed upon opening of zwitterion A at the N+–C(6) bond. The structure of the open form may be described
using three resonance structures B, C, and D. The electrophilic reaction of form B with indole leads to the
formation of pyrrolyl(indol-3-yl)arylmethanes 11a-c. The reaction of resonance forms C and D, which have an
electron-deficient site at position 2 in the pyrrole ring, with the N-indolyl anion through the 2,5-addition adduct
and a subsequent 1,5-sigmatropic shift results in formation of 1-(indol-1-yl)pyrroles 12a-c. (Indol-3-yl)-pyrroles
13a,b are likely formed in the reaction of resonance forms C and D with indole or the indol-3-yl anion. The
impossibility of forming cation B in the case of p-nitrophenyl derivative 10d probably is the reason for the
failure of this compound to undergo domino reactions with alkynes and indole.
The structures of substituted pyrroles 11a-c, 12a-c, and 13a,b were confirmed spectroscopically. The
structures of pyrroles 12a and 13a were unequivocally established by X-ray diffraction structural analysis. The
mass spectra of all the substituted pyrroles have molecular ion peaks corresponding to their empirical formulas.
1
The H NMR spectra of pyrroles 12 and 13 show signals for pyrrole ring protons H-3,4 at 6.25-6.62 ppm
1787

(3J = 3.2 Hz). The methylene group protons are seen as two AB systems at 2.97-3.58 (CH2R, J = 16.0-17.4 Hz)
and 3.63-3.95 ppm (CH2N, J = 15.8-16.5 Hz) for pyrroles 12a-c and at 2.95-3.60 (CH2R, J = 16.1-16.8 Hz) and
3.66-3.99 ppm (CH2N, J = 15.6-16.5 Hz) for pyrroles 13a,b. A singlet for the indole NH proton is found in the
spectra of pyrroles 13a,b downfield at 7.87-7.97 ppm. The spectra of all the pyrroles obtained have a downfield
doublet for the vinyl group proton overlapped with the aromatic proton signals, while a broad upfield singlet is
observed at 4.30-4.65 ppm.
R
CO2Me
N
H
+
N
Me
N
HC
10a–c
–
N
–
CO2Me
A
R
N
R
N
R
N
+
+
N
H
+
N
N
Me
Me
Me
B
C
D
CO2Me
CO2Me
CO2Me
N
H
N
N
H
–
11a–c
H
H
R
R
N
N
N
N
Me
Me
N
N
CO2Me
CO2Me
1,5-shift
12a–c
1,5-shift
13a,b
Pyrroles 11a-c, which have two chiral sites, namely, a chirality axis (atropoisomeric site due to hindered
rotation of the pyrrole and phenyl rings) and an asymmetric triarylmethyl site, are formed, as expected as a 0.7:1
diastereomer mixture for pyrrole 11a, 0.9:1 mixture for compound 11b, and 0.8:1 mixture for compound 11c as
indicated by 1H NMR spectroscopy. Thus, the spectra of these compounds have a double set of signals for each
of the protons. The 1H NMR spectrum of pyrrole 11a in DMSO at 90°C shows only set of signals related to the
disappearance of axial chirality due to rapid rotation of the pyrrole and phenyl rings.
Ph
Ph
CO2Me
NH
CO2Me
Me
Me
HC
N
N
N Me
Indole, CH2Cl2
50°C, 12 days
N
Me
14
15
1788

1
The H NMR spectrum of 1-methylpyrrole 15, obtained by the multicomponent reaction of 1-methyl-
4-phenylpyrrolobenzodiazepine 14 [11] with methyl propiolate and indole, has only one set of signals for each
proton, indicating the pyrrole 15 is formed as a single isomer.
Fig. 1. Molecular structure of pyrrole 12a with representation of the atoms
by thermal vibration ellipsoids of 50% probability.
Fig. 2. Molecular structure of pyrrole 13a with representation of the atoms
by thermal vibration ellipsoids of 50% probability.
The X-ray diffraction structural analysis data illustrated in Figures 1 and 2 for pyrroles 12a and 13a
show that these molecules differ only in the attachment of the indole substituent to the pyrrole ring, namely,
through the nitrogen atom or through a carbon atom, respectively. The benzene, indole, and phenyl fragments
are twisted relative to the central pyrrole ring in pyrrole 12a by 87.54(7), 61.89(6), and 72.75(7)° and in pyrrole
13a by 72.89(8), 23.77(9), and 89.72(8)°, respectively. The observed conformation of these molecules is
apparently stabilized by intramolecular C–H··· hydrogen bonds. The methylaminopropenoate fragment –CH2–
N(CH3)–CH=CH–(=O)–OCH3 in both compounds has (E)-configuration and takes a flattened conformation due
to the long conjugated bond chain. All the nitrogen atoms in pyrrole 12a and N(1) and N(2) in pyrrole 13a have
trigonal-plane geometry (the sum of the valence angles are 359.7, 359.6, 359.3, 358.8, and 360.0°, respectively).
On the other hand, the atom N(3) in pyrrole 13a has a slightly pyramidal configuration (the sum of the valence
angles is 357.3°) due to the formation of intermolecular hydrogen bond N(3)–H(3)···O(1) (-0.5+ x, 0.5-y,
-0.5+z) (N···O, 2.861(3) Å; H···O, 2.04(3) Å; N–H···O, 147(2)°).
Thus, we have shown that cleavage of the N+–C(Ar) bond occurs in the initially-formed ammonium
zwitterion during the transformation of 4-arylpyrrolobenzodiazepines in a three-component reaction with
methyl propiolate and indole. The resultant cation then reacts through various pathways to give different
indolylpyrroles.
1789

EXPERIMENTAL
IR spectra were recorded on an Infralum-801 Fourier spectrometer in KBr pellets. 1Н NMR spectra were
recorded on a Bruker WP-400 (400 МHz) spectrometer in CDCl3, internal standard was TMS. LG mass spectra
were recorded on a system comprising an Agilent 1100 liquid chromatograph, an Agilent Technologies LC/MSD
VL mass spectrometer (atmospheric pressure ESI), and Sedex 75 ELSD detector (compounds 8d, 9d, 12b).
Mass spectra were recorded on a Thermo Scientific MAT 95XL chromato-mass spectrometer with direct sample
insertion (electron ionization, 70 eV, compounds 10d, 12a) or on a JEOL JMS-T100LP-DART 100 instrument
(DART ionization, all other compounds). Elemental analysis was carried out on a Carlo Erba 1106 instrument.
Melting points were determined on a SMP 10 apparatus. Sorbfil and Alufol plates were used for TLC
(visualization by iodine vapor, KMnO4 and H2SO4 solutions). Silica gel from Acros (0.04-0.06 mm, 60 Å) was
used for column chromatography.
All the solvents were purified by distillation. Methyl propiolate from Acros Organics was used without
additional purification. Microwave-activated quaternization of pyrrolobenzodiazepines was performed in an
Anton Paar Monowave 300 oven.
4-Methoxy-N-[2-(1H-pyrrol-1-yl)benzyl]benzamide (8c). p-Methoxybenzoyl chloride (10.9 g,
64 mmol) was added dropwise to calcinated K2СО3 (10.5 g, 75 mmol) and 2-(pyrrol-1-yl)benzylamine (10.0 g,
58 mmol) in abs. MeCN (20 ml) at 20°С. The reaction mixture was stirred at room temperature for 2 h. The
reaction was monitored by TLC (Sorbfil, EtOAc–hexane, 1:2). The solvent was removed in vacuo. Water (40
ml) was added to the residue. The precipitate was filtered off and recrystallized from EtOAc–hexane, 1:2. Yield
1
13.3 g (92%), colorless crystals, mp 159-161°С. IR spectrum, ν, cm-1: 3343 (NH), 1631 (СО). H NMR
spectrum, δ, ppm (J, Hz): 3.83 (3Н, s, ОСН3); 4.56 (2Н, d, J = 6.0, СН2N); 5.92 (1Н, br. s, NH); 6.39 (2Н, t,
J = 2.3, H-3,4 pyrrole); 6.83 (2Н, t, J = 2.3, Н-2,5 pyrrole); 6.86 (2Н, d, J = 8.7, H-3,5 COAr); 7.27-7.40 (2Н,
m, H Ar); 7.49-7.58 (2Н, m, H Ar); 7.60 (2Н, d, J = 8.7, H-2,6 COAr). Mass spectrum, m/z: 307 [M+Н]+.
Found, %: C 74.40; H 5.72; N 9.50. C19H18N2O2. Calculated, %: C 74.49; H 5.92; N 9.14.
4-Nitro-N-[2-(1H-pyrrol-1-yl)benzyl]benzamide (8d) was obtained similarly to compound 8с from
calcinated K2СО3 (10.5 g, 75 mmol), 2-(pyrrol-1-yl)benzylamine (10.0 g, 58 mmol), and p-nitrobenzoyl
chloride (11.9 g, 64 mmol). Yield 12.1 g (65%), colorless crystals, mp 162-163°С. IR spectrum, ν, cm-1: 3324
(NH), 1633 (CO), 1542, 1343 (NO2). 1H NMR spectrum, δ, ppm (J, Hz): 4.54 (2Н, d, J = 6.4, СН2N); 5.80 (1Н,
br. s, NH); 6.41 (2Н, t, J = 2.4, H-3,4 pyrrole); 6.85 (2Н, t, J = 2.4, Н-2,5 pyrrole); 7.34-7.38 (2Н, m, H Ar); 7.40
(1Н, t, J = 4.6, H Ar); 7.52-7.54 (1Н, m, H Ar); 7.76 (2Н, d, J = 8.7, H-2,6 COAr); 8.23 (2Н, d, J = 8.7, H-3,5
COAr). Mass spectrum, m/z: 322 [M+H]+. Found, %: C 67.37; H 4.58; N 13.12. C18H15N3O3. Calculated, %:
C 67.28; H 4.71; N 13.08.
4-(4-Methoxyphenyl)-6H-pyrrolo[1,2-a][1,4]benzodiazepine (9c). POCl3 (30.0 g, 196 mmol) was added
dropwise to a solution of amide 8c (15.0 g, 49 mmol) in abs. MeCN (80 ml) under argon atmosphere. The
reaction mixture was refluxed for 3 h. The reaction was monitored by TLC (Alufol, EtOAc–hexane, 1:3). The
residue, (a dark oil) was poured into 25% ammonia solution (25 ml) and extracted with EtOAc (400 ml). The
extract was dried over MgSO4, and the solvent was removed in vacuo. The residue was triturated with Et2O, the
resulting precipitate was filtered off. Yield 10.2 g (81%), yellow crystals, mp 79-81°C. 1H NMR spectrum, δ, ppm (J,
Hz): 3.81 (3Н, s, ОСН3); 4.41 (1Н, br. s) and 4.77 (1Н, br. s, 6-СН2); 6.38 (1Н, t, J = 3.7, Н-3); 6.49 (1Н, dd, J = 2.3,
J = 3.7, Н-2); 6.86 (2Н, d, J = 8.7, H-3',5'); 7.26-7.30 (1Н, m, Н Аr); 7.33 (1Н, dd, J = 2.3, J = 1.8, Н-1); 7.35-7.39
(2Н, m, Н Аr); 7.47 (1Н, d, J = 7.3, Н Аr); 7.66 (2Н, d, J = 8.7, H-2',6'). Mass spectrum, m/z: 289 [M+Н]+. Found,
%: С 79.31; Н 5.46; N 9.68. C19H16N2O. Calculated, %: С 79.14; Н 5.59; N 9.71.
4-(4-Nitrophenyl)-6H-pyrrolo[1,2-a][1,4]benzodiazepine (9d) was obtained similarly to compound 9с
from amide 8d (15.7 g, 49 mmol) and POCl3 (30.0 g, 196 mmol). Yield 13.5 g (91%), beige crystals,
mp 165-167 °С. IR spectrum, ν, cm-1: 1577 (С=N), 1514, 1347 (NO2). 1H NMR spectrum, δ, ppm (J, Hz): 4.72
(2Н, br. s, 6-СH2); 6.42-6.47 (2Н, m, H-2,3); 7.33 (1Н, t, J = 6.0, H-8); 7.38-7.44 (3Н, m, Н-1,7,9); 7.50 (1Н, d,
1790

J = 7.3, H-10); 7.90 (2Н, d, J = 8.7, H-2',6'); 8.21 (2Н, d, J = 8.7, H-3',5'). Mass spectrum, m/z: 304 [M+H]+. Found,
%: C 71.41; H 4.28; N 13.79. C18H13N3O2. Calculated, %: C 71.28; H 4.32; N 13.85.
4-(4-Methoxyphenyl)-5-methyl-5,6-dihydro-4H-pyrrolo[1,2-a][1,4]benzodiazepine
(10с).
A
mixture of benzodiazepine 9c (0.68g, 2.7 mmol) and MeI (1.9 g, 13.6 mmol) in absolute acetone (10 ml) was
irradiated with microwaves (50 W) at 150°С for 0.5 h. The solvent was removed in vacuo. The residue was
dissolved in a mixture of MeOH (16 ml) and 60% EtOH (24 ml), and NaBH4 (0.09 g, 2.5 mmol) was added.
After 10 min at 20°С, a precipitate started to form. To this mixture, H2O (50 ml) was added, and the precipitated
crystals were filtered off and dried in air. Yield 0.70 g (86%), beige crystals, mp 96-98°C. 1H NMR spectrum, δ,
ppm (J, Hz): 2.22 (3Н, s, NСН3); 3.51 (1Н, d, J = 13.7, 6-СНА); 3.81 (3Н, s, ОСН3); 3.87 (1Н, s, 4-СН); 4.11 (1Н,
d, J = 13.7, 6-СНВ); 5.50 (1Н, br. s, Н-3); 6.13-6.15 (1Н, m, Н-2); 6.87 (2Н, d, J = 7.8, H-3',5'); 6.95 (1Н, m, Н-1);
7.28-7.33 (2Н, m, Н Ar); 7.38 (2Н, d, J = 7.8, H-2',6'); 7.41-7.46 (2Н, m, Н Ar). Mass spectrum, m/z: 305 [M+Н]+.
Found, %: С 78.79; Н 6.48; N 9.13. C20H20N2O. Calculated, %: С 78.92; Н 6.62; N 9.20.
5-Methyl-4-(4-nitrophenyl)-5,6-dihydro-4H-pyrrolo[1,2-a][1,4]benzodiazepine (10d) was obtained
similarly to compound 10с from benzodiazepine 9d (0.82 g, 2.7 mmol) and MeI (1.90 g, 13.6 mmol). Yield
1
0.72 g (83%), beige crystals, mp 150-152°С. IR spectrum, ν, cm-1: 1523, 1349 (NO2). H NMR spectrum, δ,
ppm (J, Hz): 2.24 (3Н, s, NСН3); 3.49 (1Н, d, J = 13.7) and 4.08 (1Н, d, J = 13.7, 6-СН2); 4.12 (1Н, s, 4-СН);
5.41-5.45 (1Н, m, Н-3); 6.17 (1Н, t, J = 3.2, Н-2); 6.99-7.02 (1Н, m, Н-1); 7.26-7.36 (2Н, m, Н Ar); 7.37-7.48
(2Н, m, Н Ar); 7.63 (2Н, d, J = 8.7, H-2',6'); 8.17 (2Н, d, J = 8.7, H-3',5'). Mass spectrum, m/z (Irel, %): 319
[M]+ (22), 197 (100), 154 (20), 42 (8). Found, %: С 71.60; Н 5.49; N 13.10. C19H17N3O2. Calculated, %:
С 71.46; Н 5.37; N 13.16.
Methyl (2E)-3-[(2-{2-[1H-Indol-3-yl(phenyl)methyl]-1H-pyrrol-1-yl}benzyl)(methyl)amino]acrylate
(11а), Methyl (2E)-3-[{2-[2-Benzyl-5-(1H-indol-1-yl)-1H-pyrrol-1-yl]benzyl}(methyl)amino]acrylate (12а),
Methyl (2E)-3-[{2-[2-Benzyl-5-(1H-indol-3-yl)-1H-pyrrol-1-yl]benzyl}(methyl)amino]acrylate (13а). A solution
of pyrrolobenzodiazepine 10a (0.5 g, 1.8 mmol), methyl propiolate (0.2 g, 2.2 mmol), and indole (0.3 g, 2.2 mmol)
in CH2Cl2 (15 ml) was kept at 35°С for 42 h. The reaction was monitored by TLC (Alufol, EtOAc–hexane, 1:5). The
solvent was removed in vacuo. The residue was purified by column (1.8×18 cm) chromatography on silica gel,
eluent EtOAc–hexane, 1:5. The products were eluted in order 12a, 11а and 13a.
Compound 11а. Yield 0.014 g (1.6%), colorless crystals, mp 145-147°C (Et2O–hexane). According to
its 1Н NMR spectrum, the product is a mixture of diastereomers in a ration of 0.7:1.
Minor Isomer. 1H NMR spectrum, δ, ppm (J, Hz): 2.42 (3Н, s, NСН3); 3.10 (1Н, d, J = 16.2) and 3.78
(1Н, d, J = 16.2, СН2N); 3.66 (3Н, s, ОСН3); 4.47 (1Н, br. s, =СНСО2Ме); 5.21 (1Н, s, СНPh); 5.97 (1Н, br. s,
Н-4 pyrrole); 6.22 (1Н, d, J = 3.7, Н-2 indole); 6.57 (1Н, br. s, Н-3 pyrrole); 6.66 (1Н, br. s, Н-5 pyrrole);
6.90-7.47 (14Н, m, N(Ме)–СН=, Н-4,5,6,7 indole, H Ar); 8.18 (1Н, br. s, NH).
Major Isomer. IR spectrum, ν, cm-1: 1692 (С=О), 1621 (NC=CO2СН3). 1H NMR spectrum, δ, ppm (J,
Hz): 2.44 (3Н, s, NСН3); 3.52 (1Н, d, J = 16.2) and 3.93 (1Н, d, J = 16.2, СН2N); 3.66 (3Н, s, ОСН3); 4.49 (1Н,
br. s, =СНСО2Ме); 5.21 (1Н, s, СНPh); 6.02 (1Н, br. s, Н-4 pyrrole); 6.21 (1Н, d, J = 3.7, Н-2 indole); 6.51
(1Н, br. s, Н-3 pyrrole); 6.60 (1Н, br. s, Н-5 pyrrole); 6.90-7.47 (14Н, m, N(Ме)–СН=, Н-4,5,6,7 indole, H Ar);
7.91 (1Н, br. s, NH). Mass spectrum, m/z: 476 [M+Н]+. Found, %: С 78.39; Н 6.30; N 8.58. C31H29N3O2.
Calculated, %: C 78.29; H 6.15; N 8.84.
Compound 12а. Yield 0.09 g (10.5%), colorless crystals, mp 123-125°C (Et2O–hexane). IR spectrum,
ν, cm-1: 1691 (С=О), 1619 (NC=CO2СН3). 1H NMR spectrum, δ, ppm (J, Hz): 1.76 (3Н, s, NСН3); 2.97 (1Н, d,
J = 16.0) and 3.46 (1Н, d, J = 16.0, СН2Ph); 3.61 (3Н, s, ОСН3); 3.63 (1Н, d, J = 16.0) and 3.79 (1Н, d,
J = 16.0, СН2N); 4.30 (1Н, br. s, =СНСО2Ме); 6.25 (1Н, d, J = 3.2, Н-3 pyrrole); 6.28 (1Н, d, J = 3.6, Н-3
indole); 6.34 (1Н, d, J = 3.2, Н-4 pyrrole); 6.71 (1Н, br. d, J = 7.3, H Ar); 6.72 (1Н, d, J = 3.6, Н-2 indole); 6.75
(1Н, t, J = 8.2, Н-5 indole); 6.84 (2Н, br. s, J = 6.9, Н Ar); 6.95 (1Н, br. s, N(Ме)–СН=); 7.05 (1Н, t, J = 7.3,
Н Ar); 7.16-7.22 (3Н, m, Н Ar); 7.26-7.34 (3Н, m, Н-6 indole, H Ar); 7.38 (1Н, d, J = 8.2, Н-4 indole); 7.46
(1Н, d, J = 8.2, Н-7 indole). Mass spectrum, m/z (Irel, %): 475 [M]+ (91), 369 (86), 269 (42), 244 (100), 154
(22). Found, %: С 78.39; Н 6.05; N 8.69. C31H29N3O2. Calculated, %: С 78.29; Н 6.15; N 8.84.
1791

Compound 13а. Yield 0.017 g (2.0%), colorless crystals, mp 171-173°C (Et2O). IR spectrum, ν, cm-1:
1695 (С=О), 1617 (NC=CO2СН3). 1H NMR spectrum, δ, ppm (J, Hz): 1.92 (3Н, s, NСН3); 2.95 (1Н, d, J = 16.8)
and 3.41 (1Н, d, J = 16.8, СН2Ph); 3.59 (3Н, s, ОСН3); 3.66 (1Н, s, J = 15.6) and 3.84 (1Н, d, J = 15.6, СН2N);
4.63 (1Н, br. s, =СНСО2Ме); 6.17 (1Н, d, J = 2.5, Н-2 indole); 6.32 (1Н, d, J = 3.1, Н-4 pyrrole); 6.60 (1Н, d,
J = 3.1, Н-3 pyrrole); 6.83 (1Н, t, J = 8.1, Н Ar); 6.85-6.89 (2Н, m, Н Ar); 6.97 (1Н, br. s, N(Ме)–СН=);
7.10-7.20 (6Н, m, Н Ar, Н-6,5 indole); 7.26-7.29 (1Н, m, Н Ar); 7.32-7.39 (1Н, m, Н Ar); 7.40 (1Н, d, J = 8.1,
Н-7 indole); 7.87 (1Н, s, NH); 7.88 (1Н, d, J = 8.1, Н-4 indole). Mass spectrum, m/z: 476 [M+Н]+. Found, %:
С 78.39; Н 6.09; N 8.58. C31H29N3O2. Calculated, %: C 78.29; H 6.15; N 8.84.
Methyl
(2E)-3-[(2-{2-[1H-Indol-3-yl(2-thienyl)methyl]-1H-pyrrol-1-yl}benzyl)(methyl)amino]-
acrylate (11b), Methyl (2E)-3-[{2-[2-(1H-Indol-1-yl)-5-(2-thienylmethyl)-1H-pyrrol-1-yl]benzyl}(methyl)-
amino]acrylate (12b), Methyl (2E)-3-[{2-[2-(1H-Indol-1-yl)-5-(2-thienylmethyl)-1H-pyrrol-1-yl]benzyl}-
(methyl)amino]acrylate (13b). A solution of benzodiazepine 10b (0.40 g, 1.4 mmol), methyl propiolate (0.14 g,
1.7 mmol), and indole (0.20 g, 1.7 mmol) in CH2Cl2 (15 ml) was kept at 35°С for 4 days. The reaction was
monitored by TLC (Alufol, EtOAc–hexane, 1:10). The solvent was removed in vacuo. The residue was purified
by column (1.8×30 cm) chromatography on silica gel, eluent EtOAc–hexane, 1:15. The products were eluted in
order 12b, 11b and 13b.
Compound 11b. Yield 0.15 g (18.3%), orange crystals, mp >155°C (decomp., EtOAc–hexane).
According to its 1Н NMR spectrum, the product is a mixture of diastereomers in a ratio of 0.9:1.
1
Minor Isomer. H NMR spectrum, δ, ppm (J, Hz): 2.55 (3Н, s, NСН3); 3.50 (1Н, d, J = 16.1) and 3.83
(1Н, d, J = 16.1, СН2N); 3.68 (3Н, s, ОСН3); 4.44 (1Н, br. s, =СНСО2Me); 5.49 (1Н, s, Pyrr–СН–Ind); 6.09 (1Н,
dd, J = 1.4, J = 3.2, Н-3 pyrrole); 6.27 (1Н, br. s, Н-2 indole); 6.63 (1Н, d, J = 3.2, Н-5 pyrrole); 6.73-6.75 (1Н, m,
Н-4 pyrrole); 6.75-6.76 (1Н, m, Н-3 thienyl); 6.85-6.89 (1Н, m, Н-4 thienyl); 7.01-7.05 (1Н, m, H Ar); 7.11 (1Н,
br. s, Н-5 thienyl); 7.13-7.19 (3Н, m, H Ar); 7.24-7.42 (5Н, m, =СНNCH3, H Ar); 8.37 (1Н, br. s, NH).
1
Major Isomer. IR spectrum, ν, cm-1: 1689 (С=О), 1623 (NC=CO2СН3). H NMR spectrum, δ, ppm (J,
Hz): 2.39 (3Н, s, NСН3); 3.23 (1Н, d, J = 17.0) and 3.95 (1Н, d, J = 17.0, СН2N); 3.68 (3Н, s, ОСН3); 4.54 (1Н,
br. d, J = 12.8, =СНСО2Ме); 5.47 (1Н, s, Pyrr–СН–Ind); 6.24 (1Н, t, J = 3.2, Н-3 pyrrole); 6.28 (1Н, br. s, Н-2
indole); 6.57 (1Н, br. s, Н-4 pyrrole); 6.61 (1Н, br. s, Н-5 pyrrole); 6.70-6.73 (1Н, m, Н-3 thienyl); 6.85-6.89
(1Н, m, Н-4 thienyl); 6.94-6.97 (1Н, m, H Ar); 6.98 (1Н, br. s, Н-5 thienyl); 7.13-7.19 (3Н, m, H Ar); 7.24-7.42
(5Н, m, H Ar, N(Ме)–СН=); 8.02 (1Н, br. s, NH). Mass spectrum, m/z: 482 [M+Н]+. Found, %: С 72.45;
Н 5.82; N 8.75. C29H27N3O2S. Calculated, %: C 72.32; H 5.65; N 8.72.
Compound 12b. Yield 0.032 g (4.0%), colorless crystals, mp 116-117°C (EtOAc–hexane). IR
1
spectrum, ν, cm-1: 1691 (С=О), 1617 (NC=CO2СН3). H NMR spectrum, δ, ppm (J, Hz): 1.90 (3Н, br. s,
NСН3); 3.29 (1Н, d, J = 17.4) and 3.58 (1Н, d, J = 17.4, СН2Het); 3.63 (3Н, s, ОСН3); 3.90 (1Н, d, J = 16.5)
and 3.95 (1Н, d, J = 16.5, СН2N); 4.35 (1Н, br. s, =СНСО2Ме); 6.32 (1Н, d, J = 3.2, Н-3 pyrrole); 6.34 (1Н, d,
J = 4.1, Н-3 indole); 6.39 (1Н, d, J = 3.2, Н-4 pyrrole); 6.40-6.42 (1Н, m, Н-3 thienyl); 6.75 (1Н, d, J = 4.1,
Н-2 indole); 6.81 (1Н, d, J = 6.9, H Ar); 6.85 (1Н, dd, J = 3.7, J = 5.0, Н-4 thienyl); 7.08 (2Н, t, J = 7.3, H Ar);
7.15-7.20 (2Н, m, Н-5 indole, Н-5 thienyl); 7.28-7.31 (3Н, м, Н-6 indole, N(Ме)–СН=, Н Ar); 7.42 (1Н, d,
J = 8.2, Н-4 indole); 7.50 (1Н, d, J = 7.8, Н-7 indole). Mass spectrum, m/z: 482 [M+H]+. Found, %: С 72.65;
Н 5.44; N 8.48. C29H27N3O2S. Calculated, %: С 72.32; Н 5.65; N 8.72.
Compound 13b. Yield 0.050 g (6.0%), beige crystals, mp 133-135°C (Et2O). IR spectrum, ν, cm-1:
1
1671 (С=О), 1608 (NC=CO2СН3). H NMR spectrum, δ, ppm (J, Hz): 1.98 (3Н, s, NСН3); 3.23 (1Н, d,
J = 16.1) and 3.50 (1Н, d, J = 16.1, СН2Het); 3.60 (3Н, s, ОСН3); 3.93 (1Н, d, J = 16.5) and 3.99 (1Н, d,
J = 16.5, СН2N); 4.35 (1Н, br. s, =СНСО2Ме); 6.19 (1Н, d, J = 2.3, Н-2 indole); 6.38 (1Н, d, J = 3.2, Н-4
pyrrole); 6.39 (1Н, br. s, Н-3 thienyl); 6.62 (1Н, d, J = 3.2, Н-3 pyrrole); 6.81 (1Н, t, J = 4.2, Н-4 thienyl); 6.90
(1Н, d, J = 7.3, Н Ar); 7.05 (1Н, br. s, N(Ме)–СН=); 7.10 (1Н, d, J = 5.0, Н-5 thienyl); 7.14-7.20 (2Н, m, Н-5,6
indole); 7.26-7.28 (1Н, m, Н-7 indole); 7.35-7.44 (3Н, m, Н Ar); 7.90 (1Н, d, J = 7.8, Н-4 indole); 7.97 (1Н, s,
NH). Mass spectrum, m/z: 482 [M+Н]+. Found, %: С 72.48; Н 5.71; N 8.79. C29H27N3O2S. Calculated, %:
C 72.32; H 5.65; N 8.72.
1792

Methyl
(2E)-3-[(2-{2-[1H-Indol-3-yl(4-methoxyphenyl)methyl]-1H-pyrrol-1-yl}benzyl)(methyl)-
amino]acrylate (11c), Methyl (2E)-3-[{2-[2-(1H-Indol-1-yl)-5-(4-methoxybenzyl)methyl-1H-pyrrol-1-yl]-
benzyl}(methyl)amino]acrylate (12c). A solution of pyrrolobenzodiazepine 10с (0.50 g, 1.64 mmol), methyl
propiolate (0.31 g, 3.61 mmol), and indole (0.23 g, 1.97 mmol) in CH2Cl2 (25 ml) was kept at 35°С for 3 weeks.
The reaction was monitored by TLC (Alufol, EtOAc–hexane, 1:5). The solvent was removed in vacuo. The
residue was purified by column (1.8×18 cm) chromatography on silica gel, eluent EtOAc–hexane, 1:7. The
product 12с was eluted first, then product 11с.
Compound 11с. Yield 0.04 g (4.8%), yellow crystals, mp 99-101°C (EtOAc–hexane). According to its
1Н NMR spectrum, the product is a mixture of diastereomers in a ratio of 0.8:1.
1
Minor Isomer. H NMR spectrum, δ, ppm (J, Hz): 2.44 (3Н, br. s, NСН3); 3.66 (3Н, s, ОСН3); 3.69
(1Н, d, J = 16.5) and 3.97 (1Н, d, J = 16.5, СН2N); 3.76 (3Н, s, СО2СН3); 4.49 (1Н, br. s, =СНСО2Ме); 5.16
(1Н, s, СНС6Н4ОМе); 6.00 (1Н, d, J = 3.1, Н-3 pyrrole); 6.22 (1Н, t, J = 3.1, Н-4 pyrrole); 6.55 (1Н, br. s, Н-2
indole); 6.64 (1Н, br. s, Н-5 pyrrole); 6.76 (2Н, d, J = 7.8, H Ar); 6.95 (2Н, d, J = 7.8, H Ar); 6.94-6.96 (1Н, m,
H Ar); 7.00-7.08 (2Н, m, H Ar); 7.11 (1Н, t, J = 7.3, H Ar); 7.15 (1Н, d, J = 7.8, H Ar); 7.17-7.40 (4Н, м,
N(Ме)–СН=, H Ar); 8.22 (1Н, br. s, NH).
Major Isomer. IR spectrum, ν, cm-1: 1698 (С=О), 1631 (NC=CO2СН3). 1H NMR spectrum, δ, ppm (J,
Hz): 2.44 (3Н, br. s, NСН3); 3.49 (1Н, d, J = 16.5) and 3.92 (1Н, d, J = 16.5, СН2N); 3.65 (3Н, s, ОСН3); 3.75
(3Н, s, СО2СН3); 4.49 (1Н, br. s, =СНСО2Ме); 5.15 (1Н, s, СНС6Н4OМе); 5.94 (1Н, d, J = 3.1, Н-3 pyrrole);
6.20 (1Н, t, J = 3.1, Н-4 pyrrole); 6.50 (1Н, br. s, Н-2 indole); 6.59 (1Н, br. s, Н-5 pyrrole); 6.76 (2Н, d, J = 7.8,
H Ar); 6.95 (2Н, d, J = 7.8, H Ar); 6.94-6.96 (1Н, m, H Ar); 7.00-7.08 (2Н, m, H Ar); 7.11 (1Н, t, J = 7.3,
H Ar); 7.15 (1Н, d, J = 7.8, H Ar); 7.17-7.40 (4Н, m, N(Ме)–СН=, H Ar); 7.93 (1Н, br. s, NH). Mass spectrum,
m/z: 506 [M+Н]+. Found, %: С 76.19; Н 6.01; N 8.50. C32H31N3O3. Calculated, %: C 76.02; H 6.18; N 8.31.
Compound 12с. Yield 0.03 g (3.6%), colorless crystals, mp 129-131°C (Et2O–hexane). IR spectrum, ν, cm-
1: 1695 (С=О), 1621 (NC=CO2СН3). 1H NMR spectrum, δ, ppm (J, Hz): 1.84 (3Н, s, NCH3); 3.19 (1Н, d, J = 16.5)
and 3.52 (1Н, d, J = 16.5, СН2С6Н4ОMe); 3.57 (1Н, d, J = 15.8) и 3.69 (1Н, d, J = 15.8, NCH2); 3.61 (3Н, s,
ArОCH3); 3.77 (3Н, s, СО2CH3); 4.33 (1Н, br. s, CH=СНСО2CH3); 6.21 (1Н, d, J = 2.8, H-4 pyrrole); 6.30 (1Н, d,
J = 2.8, H-3 pyrrole); 6.34 (1Н, d, J = 3.7, Н-3 indole); 6.70-6.76 (3Н, m, Н Ar); 6.77-6.84 (3Н, m, Н Ar); 7.00 (1Н,
br. s, Н-2 indole); 7.06 (1Н, t, J = 7.8, Н-5 indole); 7.15 (1Н, t, J = 7.8, Н-6 indole); 7.22-7.23 (3Н, m, N(Ме)–СН=,
H Ar); 7.39 (1Н, d, J = 7.8, Н-4 indole); 7.48 (1Н, d, J = 7.8, Н-7 indole). Mass spectrum, m/z: 506 [M+Н]+. Found,
%: С 76.12; Н 6.28; N 8.20. C32H31N3O3. Calculated, %: С 75.99; Н 6.16; N 8.29.
Methyl
(2E)-3-[(2-{2-[1H-Indol-3-yl(phenyl)methyl]-5-methyl-1H-pyrrol-1-yl}benzyl)(methyl)-
amino]acrylate (15). A solution of pyrrolobenzodiazepine 14 (0.50 g, 1.70 mmol), methyl propiolate (0.40 g,
5.20 mmol), and indole (0.24 g, 2.08 mmol) in CH2Cl2 (30 ml) was kept at 50°С for 12 days. The reaction was
monitored by TLC (Alufol, EtOAc–hexane, 1:8). The solvent was removed in vacuo. The residue was purified by
column (1.8×18 cm) chromatography on silica gel, eluent EtOAc–hexane, 1:6. Yield 0.17 g (20%), beige
1
crystals, mp 195-197°C (Et2O). IR spectrum, ν, cm-1: 1671 (С=О), 1614 (NC=CO2СН3). H NMR spectrum, δ,
ppm (J, Hz): 1.94 (3Н, s, СН3); 2.44 (3Н, s, NСН3); 3.00 (1Н, d, J = 17.0, СН2N); 3.64 (1Н, d, J = 17.0, СН2N);
3.67 (3Н, s, ОСН3); 4.49 (1Н, br. s, =СНСО2Ме); 5.08 (1Н, s, Н Ph); 5.85-5.89 (1Н, m, Н-3 pyrrole); 5.93-5.98
(1Н, m, Н-4 pyrrole); 6.49 (1Н, br. s, Н-2 indole); 7.00-7.11 (4 Н, m, Н-4,5,6,7 indole); 7.12-7.20 (2Н, m,
H Ar); 7.22-7.43 (8Н, m, N(Ме)–СН=, H Ar); 7.89 (1Н, br. s, NH). Mass spectrum, m/z: 490 [M+Н]+. Found,
%: С 78.58; Н 6.43; N 8.65. C32H31N3O2. Calculated, %: C 78.50; H 6.38; N 8.58.
X-ray Structure Investigation of Compounds 12a and 13a. Crystal of compound 12а was grown
from EtOAc–hexane (С31Н29N3O2, M 475.57). Crystal structure parameters at 100 K: crystal system triclinic,
space group Р1. Unit cell dimensions: а 8.2348(7), b 10.2414(9), c 15.3342(14) Å; α 104.142(2), β 99.437(2),
γ 90.052(2)°; V 1235.92(19) Å3; Z 2; dcalc 1.278 g/сm3; F(000) 504; µ 0.081 mm-1. Crystal of compound 13а
was grown from EtOAc–hexane (С31Н29N3O2, M 475.57). Crystal structure parameters at 100 K: crystal system
monoclinic, space group Р2l/n. Unit cell dimensions: а 17.5997(18), b 7.3471(7), c 20.602(2) Å; α 90,
β 110.045(2), γ 90°; V 2502.6(4) Å3; Z 4; dcalc 1.262 g/cm3; F(000) 1008; µ 0.080 mm-1. The unit cell parameters
1793

and reflection intensities for compounds 12a and 13a were measured on an automatic three circle diffractometer
Bruker SMART APEX-II CCD with a two-coordinated detector (MoK radiation, graphite monochromator,
φ- and -scanning). The obtained data were corrected for X-ray absorption using SADABS software [12]. The
structures were solved by the direct method and refined with the full-matrix least-squares method on F2 with
anisotropic thermal parameters for all the non-hydrogen atoms. The hydrogen atom on the amino group of
compound 13a was identified objectively from Fourier difference syntheses and refined isotropically. The
positions of other hydrogen atoms in both compounds were calculated geometrically and included in the
refinement with the fixed positional (the "rider" model) and thermal (Uiso(H) = 1.5Ueq(C) for the methyl groups
and Uiso(H) = 1.2Ueq(C) for all other groups) parameters. All calculations were performed using SHELXTL
software [13]. The atom coordinate, bond length, valence angle, and anisotropic thermal parameter tables for
compounds 12a and 13a have been deposited at the Cambridge Crystallographic Data Center (deposits CCDC
931405 and CCDC 931404).
This work was carried out with the support of the Russian Foundation for Basic Research (grants 11-03-
00164 and 13-03-09431 Ukrfa) and the Grants Council of the President of the Russian Federation (grant MK-
182.2012.03).
The authors express their gratitude to Shared Research and Educational Center of the People's
Friendship University of Russia (SREC PFUR) for taking the 1H NMR spectra.
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