Mendeleev
Communications
Mendeleev Commun., 2020, 30, 315–317
Multimolecular self-organization of acetylene and arylamines
t
into 1-aryl-3-ethyl-4-vinylpyrroles in the KOBu /DMSO system
Elena Yu. Schmidt, Nadezhda V. Semenova, Elena V. Ivanova, Igor A. Ushakov and Boris A. Trofimov*
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences,
6
64033 Irkutsk, Russian Federation. Fax: +7 3952 419 346; e-mail: boris_trofimov@irioch.irk.ru
DOI: 10.1016/j.mencom.2020.05.018
A new superbase-driven self-organization of four molecules
of acetylene with one molecule of arylamine to 1-aryl-3-
ethyl-4-vinylpyrroles in the KOBu /DMSO system has been
discovered. The process includes four acts of nucleophilic
addition to acetylene followed by intramolecular cyclization
of intermediate N,N-bis(1,3-dienyl)-N-arylamine.
HC CH
Ar NH2
HC CH HC CH
Me
t
t
KOBu /DMSO
HC CH
N
Ar
Keywords: acetylene, arylamines, pyrroles, superbases, nucleophilic addition, self-assemblies.
t
Today, a great attention is drawn to environmentally benign
chemical transformations, which are implemented as pot-,
atom-, and step-economical processes (PASE paradigm). In this
system at 80 °C for 1 h with 1a/KOBu molar ratio of 1:1
†
(entry 6). The LiOH/CsF/DMSO system appeared to be
absolutely inactive as a catalyst (entry 13). In the case of
KOH/DMSO system, the major product was 2,5-dimethyl-1-
phenylpyrrole (entries 11, 12, see Table 1). Note that other
KOBu /polar nonhydroxylic solvent systems were inefficient to
1
line, superbase-driven cascade reactions involving acetylene are
especially attractive. They usually include the formation of
several C−C and C−heteroatom bonds in a one synthetic
operation and often afford potentially useful heterocyclic
5
t
promote this reaction (entries 8–10).
2
compounds. Under these conditions, acetylene behaves as a
To examine the functional group tolerance of this unexpected
assembly of pyrroles, three halo-substituted in the benzene ring
arylamines 1b–d were used in the reaction with acetylene under
the above conditions. In this way, the expected pyrroles 2b–d
were obtained in modest yields (see Scheme 2). Halogens as
substituentsprovideadditionalopportunitiesforfunctionalization
of the pyrroles obtained. Modest yields of the target products 2
triggering, driving and organizing molecule toward other
reactants. Most of these assemblies are launched by the
nucleophilic addition to the triple bond in simple and readily
available superbase systems like alkali metal hydroxides or
3
alkoxides/DMSO (pK ~ 30–32). In such systems, electro-
a
philicity of the acetylene is increased due to complexation with
alkali metal cation, and nucleophilicity of the reactants attacking
the triple bond also becomes stronger because of their desolvation.
Over the last few years, we have found a number of examples of
the superbase-promoted self-organization of complex molecules
involving several molecules of acetylene. Now there comes an
understanding that this phenomenon is fairly general.4
†
t
The reaction of arylamines 1a–d with acetylene in the KOBu /DMSO
system (typical procedure). A mixture of arylamine 1a–d (10 mmol) and
KOBu (10 mmol, 1.12 g) in DMSO (50 ml) was placed into a 0.25 dm
steel Parr reactor equipped with mechanical stirrer and manometer. The
reactor was fed with acetylene under pressure from commercially
available acetylene cylinder (initial pressure at ambient temperature was
12 atm) and then decompressed to atmospheric pressure to remove air.
The reactor was fed with acetylene again and heated (80 °C) for 1 h. The
mixture after cooling to room temperature was diluted with H2O (100 ml)
t
3
Just recently, we have described the self-assembly of 1-aryl-
~
2
,5-dimethylpyrroles with participation of three molecules of
acetylene and one molecule of arylamine in the KOH/DMSO
5
superbase system (100 °C, 3 h, Scheme 1). In this paper, we
and extracted with Et O (7×25 ml). The combined organic extracts were
2
disclose one more astonishing result of superbase-mediated self-
organization of four molecules of acetylene and one molecule of
arylamines 1a–d into 1-aryl-3-ethyl-4-vinylpyrroles 2a–d
washed with H O (3×20 ml) and dried over K CO . Diethyl ether was
2
2
3
evaporated, and the crude product 2a–d was eluted with n-hexane from
the SiO -packed column.
2
(Scheme 2).
3
-Ethyl-1-phenyl-4-vinyl-1H-pyrrole 2a. Compound 2a was prepared
It turned out, on example of the reaction between aniline 1a
from aniline 1a (10 mmol, 0.93 g), yellow oil, yield 0.31 g (20%, based
and acetylene (Table 1), that the crucial factor for implementation
of the synthesis of these rarely substituted pyrroles is the fine
tuning of the superbase system and reaction conditions. The best
on 1a consumed). Unreacted aniline 1a (0.19 g, 80% conversion) was
1
also recovered upon column chromatography.
H
NMR, d:
o
m
p
5
7
.41–7.36 (m, 4H, H , H ), 7.24–7.20 (m, 1H, H ), 7.17 (d, 1H, H ,
4
2
3
t
J 2.2 Hz), 6.85 (m, 1H, H ), 6.66 (dd, 1H, CH=CH2, J 17.7 Hz,
J 11.3 Hz), 5.45 (dd, 1H, CH=CH , J 17.7 Hz, J 1.6 Hz), 5.05 (dd, 1H,
yield of pyrrole 2a (20%) was achieved in the KOBu /DMSO
3
3
2
2
3
2
3
CH=CH , J 11.3 Hz, J 1.6 Hz), 2.63 (q, 2H, CH , J 7.4 Hz), 11.27
2
2
3
13
i
m
p
(t, 3H, Me, J 7.4 Hz). C NMR, d: 140.0 (C ), 129.4 (C ), 129.2 (C ),
KOH/DMSO
Ar NH2
+
HC CH
Me
Me
3
4
o
5
129.1 (HC=CH ), 129.9 (C ), 123.3 (C ), 119.8 (C ), 116.9 (C ), 116.7
N
2
2
–1
(
C ), 110.4 (HC=CH ), 19.1 (CH ), 14.3 (Me). IR (film, n/cm ): 2964,
1
2 2
Ar
2
927, 2873, 1599, 1520, 1512, 1371, 1225, 1061, 889, 757, 694. HRMS
+
Scheme 1
(ESI), m/z: 198.1288 [M+H] (calc. for C H N, m/z: 198.1277).
14 16
©
2020 Mendeleev Communications. Published by ELSEVIER B.V.
–
315 –
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.