Skeletal Diversity in Catalytic Synthesis of (1,3-Oxazacycloalk-3-ylmethyl)-Substituted Pyrroles

Article abstract of DOI:10.1134/S1070363219090056

A series of bi- and trinuclear pyrrole derivatives was prepared by the 5 mol % ZrOCl₂ ·8H₂O-catalyzed CH-sp²-aminomethylation reaction of pyrrole with bis(1,3-oxazacycloalk-3-yl)methanes. The reaction proceeds at the positions 2, 5 or 2 of pyrrole depending on the amount of aminomethylating reagents obtained from formaldehyde and α,ω-amino alcohols (2-aminoethan-1-ol, 3-aminopropan-1-ol, 4-aminobutan-1-ol). The aminomethylation reaction of indole with bis(1,3-oxazolidin-3-yl)methane proceeds at the position 3. In the case of carbazole, N-aminomethylation proceeds under these conditions.

Full text of DOI:10.1134/S1070363219090056

ISSN 1070-3632, Russian Journal of General Chemistry, 2019, Vol. 89, No. 9, pp. 1760–1764. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Obshchei Khimii, 2019, Vol. 89, No. 9, pp. 1346–1351.
Skeletal Diversity in Catalytic Synthesis
of (1,3-Oxazacycloalk-3-ylmethyl)-Substituted Pyrroles
V. R. Akhmetovaa, b*, E. M. Bikbulatovaa, R. V. Kunakovab, K. L. Ametac, and A. G. Ibragimova
a Institute of Petrochemistry and Catalysis, Ufa Federal Research Center of Russian Academy of Sciences,
pr. Oktyabrya 141, Ufa, 450075 Russia
*e-mail: vnirara@mail.ru
b Ufa State Petroleum Technical University, Ufa, Russia
с Department of Chemistry, School of Sciences, Mody University of Science and Technology, Rajasthan, India
Received April 9, 2019; revised April 9, 2019; accepted April 12, 2019
Abstract—Aseries of bi- and trinuclear pyrrole derivatives was prepared by the 5 mol % ZrOCl2·8Н2О-catalyzed
CH-sp2-aminomethylation reaction of pyrrole with bis(1,3-oxazacycloalk-3-yl)methanes. The reaction proceeds
at the positions 2, 5 or 2 of pyrrole depending on the amount of aminomethylating reagents obtained from formal-
dehyde and α,ω-amino alcohols (2-aminoethan-1-ol, 3-aminopropan-1-ol, 4-aminobutan-1-ol). The aminomethyl-
ation reaction of indole with bis(1,3-oxazolidin-3-yl)methane proceeds at the position 3. In the case of carbazole,
N-aminomethylation proceeds under these conditions.
Keywords: pyrrole, indole, carbazole, amino alcohols, formaldehyde, aminomethylation
DOI: 10.1134/S1070363219090056
Aromatic compounds containing dihydro- and tetra-
hydro-1,3-oxazole moieties have neurotransmitter proper-
ties [1–4]. [3+2] Cyclocondensation of α-functionalized
benzyl alcohol with guanidine or [4+1] cyclocondensa-
tion with bromine [2–4] is used to form phenyl-substi-
tuted 1,3-oxazole rings, for example, in the synthesis
of pemoline or aminorex drugs. Fused pyrrolo[1,2-c]-
oxazol-1-ones and oxazolo[3,4-a]indol-1-ones have been
obtained by a multistep method [5]. There are no data on
the synthesis of 1,3-oxazol-3-yl-, 1,3-oxazinan-3-yl- and
1,3-oxazepan-3-yl substituted pyrroles.
catalyst. The choice of the catalyst is due to its activity in
the reactions of CH-sp2-aminomethylation of pyrrole and
indole, as well as N-aminomethylation of carbazole [8].
The aminomethylating reagent, bis(1,3-oxazolidin-
3-yl)methane 1, was obtained by condensation of
2-aminoethan-1-ol with paraform (Scheme 1) [9]. In this
reaction, bicyclo[4.4.1]-1,6-diaza-3,8-dioxaundecane 2
(30–35%) was also formed as a result of intermolecular
heterocyclization of two 2-aminoethan-1-ol molecules
with 3 moles of formaldehyde [10]. Under the reaction
conditions, reactive bis(1,3-oxazolidin-3-yl)methane 1,
apparently, eliminates the oxazolidine molecule with the
formation of aminomethylating intermediate A.
In continuation of studies on the synthesis of new
pharmacologically active derivatives of a number of
azoles [6], we synthesized di- and trinuclear compounds
with pyrrole and tetrahydro-1,3-oxazole rings in the
molecules, as well as their six- and seven-membered
cyclic homologs—1,3-oxazinanes and 1,3-oxazepanes.
Hybrid molecules with pyrrole pharmacophore (indole,
carbolines, carbazole) are promising as multi-agent neu-
roprotective substances [7].
ZrOCl2·8H2O-catalyzed reaction of pyrrole with
bis(1,3-oxazolidin-3-yl)methane 1 in a ratio of 1 : 2
leads to the formation of trinuclear 2,5-bis(1,3-isoxa-
zolidin-3-ylmethyl)-1H-pyrrole 3 with a yield of 65%.
The reaction selectively takes place at a reagent ratio of
1 : pyrrole = 1 : 1 with the formation of the binuclear
derivative, 2-(1,3-isoxazolidin-3-ylmethyl)-1H-pyrrole
4, with a yield of 74% (Scheme 2). Similar reactions
with indole and carbazole afforded 3-(1,3-isoxazolidin-
3-ylmethyl)-1H-indole 5 (87%) and 9-(1,3-isoxazolidin-
3-ylmethyl)-9H-carbazole 6 (52%), respectively.
We proposed a new method for the synthesis of
tetrahydro-1,3-isoxazolidin-3-yl substituted pyrroles,
indoles, and carbazoles based on the aminomethylation
reaction in the presence of 5 mol % of ZrOCl2·8H2O as a
1760

SKELETAL DIVERSITY IN CATALYTIC SYNTHESIS
1761
Scheme 1.
N
O
C
6H6
,
(CH
2O)n
+
O
N
N
O
O
N
H2N
OH
ꢀ
H
2O
2
1
[Zr]
H+
O
+
N
O
N
HN
O
O
N
CH2+
A
[Zr]
Scheme 2.
1/2
N
H
N
N
N
H
O
[Zr]
O
3
N
N
H
N
[Zr]
H
N
N
H
N
O
N
O
O
[Zr]
[Zr]
O
N
H
4
1
5
N
H
[Zr]
N
N
O
6
Structure of the obtained compounds was confirmed
observed. The mass spectra (MALDI TOF/TOF) of 5–7
contain strong peaks of molecular ions [M + H]+.
1
by H and 13C NMR spectroscopy, as well as by mass
spectrometry. In the 1H NMR spectra, the signals of the
protons of the pyrrole ring resonate at 5.9 (3) and 5.9, 6.7,
7.3 ppm (4). The methylene protons between the pyrrole
and oxazolidine rings are observed at 3.7 ppm. The NH
protons are in the 7.20–9.35 ppm region. The signals
of the methylene protons of the oxazolidine fragment
located between the nitrogen and oxygen atoms appear
as a broadened singlet at 4.3 ppm, while the protons of
the СН2СН2 fragment of the oxazolidine ring resonate as
triplets at 3.0 ppm (at the nitrogen atom) and 3.8 ppm (at
the oxygen atom) with J = 6.8 Hz. In the spectra of com-
pounds 5 and 6 along with the signals of the oxazolidine
ring, the corresponding signals of the aromatic ring are
The proposed methodology was successfully imple-
mented for the synthesis of a variety of polyheterocycles,
such as (1,3-oxazinan-3-yl- and 1,3-oxazepan-3-yl)-
methyl substituted pyrroles 9–12 using compounds 7 and
8 obtained by heterocyclization of 3-aminopropan-1-ol
or 4-aminobutan-1-ol with formaldehyde. Depending on
the ratio of reactants 7 (or 8) : pyrrole = 2 : 1 or 1 : 1,
the CH-sp2-aminomethylation reaction of pyrrole in the
.
presence of 5 mol % ZrOCl2 8Н2О gave rise to the cor-
responding tri- or binuclear pyrrole derivatives.
The mass spectra of compounds 9–12 contain the
corresponding peaks of positive ions [M + H]+. For the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 9 2019

1762
AKHMETOVA et al.
Scheme 3.
n
n
n
'
2
+
CH O
3
2
NH2
OH
N
N
O
O
H
C6
6
7, 8
[Zr]
60o
H
C6 5CH3
,
C
1/2
N
N
H
H
O
O
O
n
n
n
N
N
N
N
N
H
H
11, 12
9, 10
n = 1 (7, 9, 11), 2 (8, 10, 12).
NMR spectra of compound 9, the signal assignments were
made using heteronuclear NMR spectroscopy techniques.
In the HSQC spestra, the following correlations were
found: the methylene proton multiplet at 1.66 ppm gives
a cross peak with a carbon atom signal at 22.03 ppm,
the methylene proton triplet at 2.83 ppm with the carbon
atom signal at 49.2 ppm, triplet of methylene protons
at 3.82 ppm correlates with a signal of carbon atoms at
68.8 ppm; a broadened singlet of methylene protons
at 4.25 ppm gives a cross peak with a signal of carbon
atoms at 84.4 ppm, a singlet of protons of the aromatic
ring at 5.92 ppm interacts with a signal of a carbon atom
at 107.2 ppm.
the method of diffusion into agar [11]. Phytopathogenic
fungi Fusarium oxysporum, Bipolaris sorokiniana, and
Rhizoctonia solani, the causative agents of various dis-
eases of crops, were used as test objects. Compound 3
has a fungistatic effect on Rhizoctonia solani, delays its
growth and promotes the formation of atypical mycelium.
The remaining compounds do not affect the growth of
microscopic fungi.
In summary, a series of (1,3-oxazacycloalk-3-ylme-
thyl)pyrrole derivatives based on formaldehyde, α,ω-
aminoalcohols and pyrrole was obtained by ZrOCl2·
8Н2О-catalyzed СН-sp2-aminomethylation reaction of
pyrrole at positions 2, 5 or 2 depending on the reagents
ratio.Asimilar reaction with indole takes place involving
the position 3, and carbazole under these conditions
reacts at the N9 atom.
1
In the H–13C HMBC spectrum, there are hetero-
nuclear spin-spin interactions between the signals of acy-
clic methylene protons at the nitrogen atom at 3.74 ppm
with the carbon atoms of the aromatic ring at 107.2 and
128.5 ppm, as well as the signals of acyclic methylene
protons at the nitrogen atom at 3.74 ppm with the carbons
of the oxazinane ring at 49.2 and 84.4 ppm (Scheme 4).
Cross peaks between the signals of methylene protons of
the oxazinane fragment are also observed.
EXPERIMENTAL
Mass spectra were recorded on a Bruker MALDI TOF/
TOF Autoflex III spectrometer, sinapinic acid was used
as a matrix. A sample was prepared by drying a drop of a
substance in chloroform (1 : 10). IR spectra were recorded
on a Bruker Vertex-70V Fourier spectrometer from liquid
paraffin. 1H, 13C NMR spectra were registered on a Bruker
Ascend III HD 500 spectrometer (500, 125 MHz) from
CDCl3 relative to internal TMS. Homo- and heteronuclear
two-dimensional experiments were performed using
standard Bruker pulse sequences. The reaction progress
was monitored by TLC on Sorbfil plates, eluting with
hexane‒EtOAc (1 : 2) and detecting with iodine vapors.
Compounds 3–5 are soluble in water and therefore
suitable for use as bioregulators in an aqueous medium.
For these compounds fungicidal activity was studied by
Scheme 4.
O
N
O
N
N
H
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 9 2019

SKELETAL DIVERSITY IN CATALYTIC SYNTHESIS
1763
General procedure for the synthesis of compounds
1, 7, 8. A mixture of 0.45 g (15 mmol) of paraformalde-
hyde and 10 mmol of the corresponding amino alcohol
(2-aminoethane-1-ol, 3-aminopropan-1-ol, 4-aminobu-
tane-1-ol) and 25 mL of benzene was refluxed with a
Dean–Stark trap for 5 h. After distilling off water, the
reaction mixture was cooled and evaporated. The target
compounds were isolated in 70–100% yields. The physi-
co-chemical characteristics of compound 1 corresponded
to those given in [9].
NMR spectrum, δС, ppm: 51.03 (C6,12), 55.05 (C 4,17),
63.03 (С5,16), 86.28 (С2,14), 107.20 (С10,11), 128.23 (C7,9).
Mass spectrum, m/z: 153.0956 [M + H]+ (calculated for
С8Н12N2O: 152.0950).
3-(1,3-Oxazolidin-3-ylmethyl)-1H-indole (5). A
mixture of 0.12 g (1 mmol) of indole, 0.16 g (1 mmol)
of bis(oxazolidin-3-yl)methane, 3 mL of toluene and
0.016 g (0.05 mmol) of ZrOCl2∙8H2O was stirred at
60°С for 6 h. After cooling, the reaction mixture was
passed through a SiO2 layer. Yield 87%, yellow oil. 1Н
NMR spectrum, δ, ppm: 2.30 s (2Н, ССН2N), 3.47 s
(2Н, СH2O), 3.46 s (2СН2, NCH2O), 3.80 s (2Н, СH2N),
7.12‒7.53 s (5НAr), 10.20 s (1Н, NH). 13С NMR spec-
trum, δС, ppm: 49.03 (C6), 56.05 (C4), 63.03 (С5), 89.28
(С2), 112.20 (С14), 112.39 (C7), 119.63 (C11), 120.34
(C12), 121.14 (C13), 126.19 (C8), 127.23 (C15), 136.75
(C10). Mass spectrum, m/z: 203.1322 [M + H]+ (calculated
for С12Н14N2O: 202.1106).
Bis(1,3-oxazinan-3-yl)methane (7). Yield 97%,
1
colorless liquid. Н NMR spectrum, δ, ppm: 1.56 m
(4Н, СН2), 2.93 t (4Н, СH2N, J = 4.8 Hz), 3.65 s (4Н,
ArСH2N), 3.78 t (2Н, СН2O, J = 4.8 Hz), 4.32 s (4Н,
NСH2O). 13С NMR spectrum, δС, ppm: 22.4 (CH2), 47.7
(СH2N), 68.0 (ArСH2N), 68.8 (СН2O), 82.9 (NСH2O).
Mass spectrum, m/z: 187.1445 [M + H]+ (calculated for
С9Н18N2O2: 186.1368).
Bis(1,3-oxazepan-3-yl)methane (8). Yield 92%,
colorless liquid. Н NMR spectrum, δ, ppm: 1.56 br. s
9-(1,3-Oxazolidin-3-ylmethyl)-9H-carbazole (6)
was obtained similarly from 0.12 g (1 mmol) of carba-
zole, 0.16 g (1 mmol) of bis(oxazolidin-3-yl)methane
and 0.016 g (0.05 mmol) ZrOCl2∙8H2O. Yield 69%, yel-
low oil. 1Н NMR spectrum, δ, ppm: 3.10 t (2Н, ССН2N,
J = 6.8 Hz), 3.70 t (2Н, ССН2О, J = 6.8 Hz), 5.42 s (2Н,
СArСH2N), 4.32 br. s (4Н, NСH2O); 7.19 s, 7.18 s and
8.64 s (3Н, СНAr) 13С NMR spectrum, δС, ppm: 52.03
(CH2), 48.8 (СH2N), 63.6 (ArСH2N), 65.9 (СН2O),
85.0 (NСH2O); 109.2, 119.3, 120.5, 122.3, 125.7, 143.4
(CAr). Mass spectrum, m/z: 252.1718 [M]+ (calculated for
С16Н16N2O: 252.1263).
1
(4Н, СН2), 1.72 br. s (4Н, СН2), 2.44 t (4Н, СH2N, J =
6.0 Hz), 3.65 s (4Н, ArСH2N), 3.78 d (2Н, СН2O, J =
6.0 Hz), 4.28 d (4Н, NСH2O, J = 6.1 Hz), 4.42 d (4Н,
NСH2O, J = 6.1 Hz). 13С NMR spectrum, δС, ppm: 24.3
(CH2), 27.0 (CH2), 50.3 (СH2N), 62.2 (ArСH2N), 69.1
(СН2O), 83.8 (NСH2O). Mass spectrum, m/z: 215.1081
[M + H]+ (calculated for С11Н22N2O2: 214.1681).
General procedure for the synthesis of (oxa-
zolidin-3-ylmethyl)-1H-pyrroles 3, 4. A mixture of
0.07 mL (1 mmol) pyrrole, 0.16 g (1 mmol, when pre-
paring compound 4) or 0.32 g (2 mmol, when preparing
compound 3), 3 mL of toluene and 0.016 g (0.05 mmol)
ZrOCl2∙8H2O was stirred at 60°С for 6 h. After cooling,
the reaction mixture was passed through a SiO2 layer.
2,5-Bis(1,3-oxazinan-3-ylmethyl)-1H-pyrrole (9)
was obtained similarly to compound 3 from pyrrole and
reagent 7 in a 1 : 2 ratio. Yield 79%, yellow oil. 1Н NMR
spectrum, δ, ppm: 1.66 m (4Н, СН2), 2.83 t (4Н, СH2N,
J = 5.5 Hz), 3.74 s (4Н, ArСH2N), 3.82 t (4Н, СН2O,
J = 5.1 Hz), 4.25 s (4Н, NСH2O), 5.92 d (2Н, СН2, J =
2.3 Hz), 8.7 s (1Н, NH). 13С NMR spectrum, δС, ppm:
22.03 (CH2), 48.8 (СH2N), 49.2 (ArСH2N), 67.9 (СН2O),
84.4 (NСH2O); 107.2, 128.5 (CAr). Mass spectrum, m/z:
266.17 [M + H]+ (calculated for С14Н23N3O2: 265.1790).
2,5-Bis(oxazolidin-3-ylmethyl)-1H-pyrrole (3).
Yield 65%, yellow oil. 1Н NMR spectrum, δ, ppm: 3.00
t (4Н, ССН2N, J = 6.8 Hz), 3.68 br. s (4Н, СArСH2N),
3.79 t (4Н, ССН2О, J = 6.8 Hz), 4.32 br. s (4Н, NСH2O),
5.94 d (2Н, СН2, J = 2.4 Hz), 7.20 s (1Н, NH). 13С NMR
spectrum, δС, ppm: 51.03 (C6,12), 55.05 (C 4,17), 63.03
(С5,16), 86.28 (С2,14), 107.20 (С10,11), 128.23 (C7,9).
Mass spectrum, m/z: 238.298 [M + H]+ (calculated for
С12Н19N3O2: 237.1477).
2-(1,3-Oxazinan-3-ylmethyl)-1H-pyrrole (11) was
obtained similarly to compounds 5 and 6 from pyrrole and
reagent 7 in a 1 : 1 ratio. Yield 80%, yellow oil. 1Н NMR
spectrum, δ, ppm: 1.61 m (2Н, СН2), 2.99 t (2Н, СH2N,
J = 5.5 Hz), 3.74 s (2Н, ArСH2N), 3.85 t (2Н, СН2O,
J = 5.1 Hz), 6.24 s (НAr), 6.76 s (НAr), 7.37 s (НAr), 9.4 s
(1Н, NH). 13С NMR spectrum, δС, ppm: 22.47 (CH2), 47.8
(СH2N), 68.0 (ArСH2N), 73.8 (СН2O), 83.0 (NСH2O);
2-(Oxazolidin-3-ylmethyl)-1H-pyrrole (4). Yield
74%, yellow oil. 1Н NMR spectrum, δ, ppm: 3.02 t (2Н,
ССН2N, J = 6.8 Hz), 3.68 br. s (2Н, СArСH2N), 3.81 t
(2Н, ССН2О, J = 6.8 Hz), 4.30 br. s (4Н, NСH2O); 5.91
s, 6.70 s and 7.34 s (3Н, СНAr), 7.20 s (1Н, NH). 13С
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 9 2019

1764
AKHMETOVA et al.
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107.7, 117.7, 128.37 (СAr). Mass spectrum, m/z: 167.11
[M + H]+ (calculated for С9Н14N2O: 166.1106).
2,5-Bis(1,3-oxazepan-3-ylmethyl)-1H-pyrrole (10)
was obtained similarly to compound 3 from pyrrole and
reagent 8 in a 1 : 2 ratio. Yield 63%, yellow oil. 1Н NMR
spectrum, δ, ppm: 1.55‒1.60 m (4Н, СН2), 2.31 t (4Н,
СH2N, J = 5.5 Hz), 3.73 s (4Н, ArСH2N), 3.82 t (4Н,
СН2O, J = 5.1 Hz), 4.25 s (4Н, NСH2O), 5.98 d (2Н,
СН2, J = 2.3 Hz), 9.7 s (1Н, NH). 13С NMR spectrum,
δС, ppm: 24.3, 25.7 (CH2), 48.8 (СH2N), 49.2 (ArСH2N),
67.9 (СН2O), 84.4 (NСH2O); 107.2, 128.5 (CAr). Mass
spectrum, m/z: 294.4050 [M + H]+ (calculated for
С16Н27N3O2: 293.2103).
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2-(1,3-Oxazepan-3-ylmethyl)-1H-pyrrole (12) was
obtained similarly to compounds 5 and 6 from pyrrole
and reagent 8 in a 1 : 1 ratio. Yield 70%, yellow oil. 1Н
NMR spectrum, δ, ppm: 1.54‒1.61 m (2Н, СН2), 2.47
t (2Н, СH2N, J = 5.5 Hz), 3.75 s (2Н, ArСH2N), 3.87
t (2Н СH2N, J = 5.1 Hz), 5.97 s (НAr), 6.54 s (НAr),
7.35 s (НAr), 9.1 s (1Н, NH). 13С NMR spectrum, δС,
ppm: 24.3, 25.4 (CH2). 49.3 (СH2N), 53.6 (ArСH2N),
70.8 (СН2O), 82.7 (NСH2O); 107.5, 117.8, 128.4 (СAr).
Mass spectrum, m/z: 181.2781 [M + H]+ (calculated for
С10Н16N2O: 180.1263).
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FUNDING
The authors are grateful to the Center for Collective
Use “Agidel” of Institute of Petrochemistry and Catalysis
of the Ufa Federal Research Center of the RussianAcad-
emy of Sciences for structural studies of compounds, as
well as N.F. Galimzyanova for the study of fungicidal
activity.
https://doi.org/10.1134/S1070428018050056
9. Salas-Coronado, R., Gálvez-Ruiz, J.C., Guadarrama-
Pérez, C., and Flores-Parr, A., Heterocycles, 2003,
vol. 60, no. 5, p. 1111.
https://doi.org/10.3987/COM-03-9713
This work was financially supported by the Russian
Foundation for Basic Research (project no. 17-43-
020292р_а) and theAcademy of Sciences of the Republic
of Bashkortostan in the frame of the project part of the
governmental task (no. AAAA-A19-119022290010-9).
10. Khabibullina, G.P., Yanybin, V.M., Ibragimov, A.G.,
and Dzhemilev, U.M., Chem. Heterocycl. Compd.,
2014, vol. 50, p. 726.
https://doi.org/10.1007/s10593-014-1527-y
11. Akhmetova, V.R., Bikbulatova, E.M., Akhmadi-
ev, N.S., Galimzyanova, N.F., Kunakova, R.V., and Ibragi-
mov, A.G., Chem. Heterocycl. Compd., 2018, vol. 54,
no. 5, p. 520.
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
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1. RF Patent 2384574, 2008.
https://doi.org/10.1007/s10593-018-2299-6
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 9 2019