Synthesis of 2-aryl-4,6-dinitrobenzo[b]thiophenes from 2,4,6- trinitrotoluene

Article abstract of DOI:10.1070/MC2004v014n01ABEH001859

A method for the synthesis of previously unknown 2-aryl-4,6-dinitrobenzo[b] thiophenes and their 3-chloro derivatives has been developed based on the replacement of ortho-NO₂ in (E)-2,4,6-trinitrostilbenes on treatment with PhCH₂SH/K₂CO₃ followed by transformations of the resulting 2-benzylthio-4,6-dinitrostilbenes by treatment with SO ₂Cl₂.

Full text of DOI:10.1070/MC2004v014n01ABEH001859

Mendeleev Commun., 2004, 14(1), 27–28
Synthesis of 2-aryl-4,6-dinitrobenzo[b]thiophenes from 2,4,6-trinitrotoluene
Oleg Yu. Sapozhnikov, Vasily V. Mezhnev, Mikhail D. Dutov, Vadim V. Kachala and Svyatoslav A. Shevelev*
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
Fax: +7 095 135 5328; e-mail: Shevelev@ioc.ac.ru
DOI: 10.1070/MC2004v014n01ABEH001859
A method for the synthesis of previously unknown 2-aryl-4,6-dinitrobenzo[b]thiophenes and their 3-chloro derivatives has been
developed based on the replacement of ortho-NO2 in (E)-2,4,6-trinitrostilbenes on treatment with PhCH2SH/K2CO3 followed by
transformations of the resulting 2-benzylthio-4,6-dinitrostilbenes by treatment with SO2Cl2.
This work is a part of a program on the study of the chemistry
R
R
of 2,4,6-trinitrotoluene (TNT). This program is aimed at the
creation of scientific bases and technologies for using TNT as
an accessible raw chemical for various purposes,1,2 including
the synthesis of polyfunctional annelated heterocyclic structures.2
It is known that TNT smoothly undergoes condensation with
aromatic and heteroaromatic aldehydes to give corresponding
(E)-2,4,6-trinitrostilbenes 1 (see ref. 3 and references therein).
It was also found that the ortho-NO2 group in stilbenes 1 is
regiospecifically replaced by the N3 group on treatment with
NaN3 under mild conditions (20 °C, DMF).3
SO2Cl2
O2N
SCH2Ph
O2N
SCl
Our study of nucleophilic substitution for the nitro group in
trinitrostilbenes 1 showed that, even at room temperature, the
treatment of stilbenes 1a–d with PhCH2SH in the presence of
an equimolar amount of K2CO3 as a deprotonating agent in NMP
or DMF results in the replacement of the nitro group by the
PhCH2S fragment. The reaction occurs at both ortho and para
positions, but ortho-substitution predominates: the ortho:para
isomer ratio for sulfides 2 and 2' is 3:1, irrespective of the
type of the substituent R in the aryl fragment (Scheme 1). The
ortho:para isomer ratio was determined from 1H NMR data for
raw reaction products (the signals of the dinitrophenyl fragment
were compared).
NO2
2a–d
NO2
3a–d
2 SO2Cl2
NO2
Cl
R
S
O2N
NO2
Cl
6a,d
R
S
SO2Cl2
NO2
O2N
R
4a–d
– HCl
a R = H
b R = Cl
c R = OMe
d R = CF3
R
S
O2N
O2N
NO2
O2N
NO2
5a–d
PhCH2SH
ArCHO
Scheme 2
NMP, K2CO3
It is known4 that the cleavage of the PhCH2–SAr bond
readily occurs on treatment with chlorinating reagents to give
the corresponding aryl sulfenyl chlorides and PhCH2Cl.5 It
could be expected that, in similar transformations of ortho-
benzylthio derivatives 2a–d, the resulting products with the
ortho-SCl fragment would be capable of intramolecular cycliza-
tion due to the addition of this fragment to the double bond.
With this purpose, sulfides (2 + 2')a–d were treated with
sulfuryl chloride in dichloroethane without separation. The use
of equimolar amounts of SO2Cl2 and (2 + 2')a–d at room
temperature results in hitherto unknown 2-aryl-4,6-dinitro-
benzo[b]thiophenes 5a–d (Scheme 2). The structures of these
compounds were established using the NOE method. This
experiment showed that the H-2 and H-6 protons of the aryl
substituent interact with the proton at the 3-position of the
benzothiophene ring. It was shown for sulfides 2a,b as an
example that the use of two equivalents of SO2Cl2 resulted in
2-aryl-3-chloro-4,6-dinitrobenzo[b]thiophenes 6a,b due to the
chlorination of benzothiophenes 5a,b formed originally, since
the reaction of compounds 5a,b with one equivalent of SO2Cl2
under the same conditions gave chlorinated derivatives 6a,b
(Scheme 2).
NO2
TNT
NO2
1a–d
R
R
O2N
SCH2Ph
O2N
NO2
NO2
SCH2Ph
2a–d, 54–86%, o:p = 3:1
a R = H
b R = Cl
c R = OMe
d R = CF3
It can be assumed that originally formed ortho-sulfenyl
chloride 3 undergoes cyclisation to give 2-aryl-3-chloro-2,3-
dihydrobenzo[b]thiophenes 4, which undergo aromatisation by
Scheme 1
– 27 –

Mendeleev Commun., 2004, 14(1), 27–28
References
eliminating HCl under the reaction conditions to give benzo-
thiophenes 5 (Scheme 2).† In fact, in the case of sulfide 2c, we
succeeded in isolating corresponding 3-chloro-2,3-dihydro-
benzo[b]thiophene 4c from the reaction mixture; on a prolonged
exposure to the reaction conditions (SO2Cl2, dichloroethane,
20 °C), this compound eliminates HCl to give compound 5c,
which confirms the above assumption.
A similar method for the synthesis of benzo[b]thiophenes
was previously known only for cinnamic acid derivatives; in the
case of these compounds, bases were required for the aroma-
tisation of the originally formed 3-chloro-2,3-dihydrobenzo-
[b]thiophenes.5 No base is required in the synthesis of 2-aryl-
4,6-dinitrobenzo[b]thiophenes 5a–d as the dehydrochlorination
occurs spontaneously.
1 V. A. Tartakovsky, S. A. Shevelev, M. D. Dutov, A. Kh. Shakhnes, A. L.
Rusanov, L. G. Komarova and A. M. Andrievsky, in Conversion
Concepts for Commercial Applications and Disposal Technologies of
Energetic Systems, ed. H. Krause, Kluwer Academic Publishers,
Dordrecht, 1997, pp. 137–149.
2 S. A. Shevelev, V. A. Tartakovsky and A. L. Rusanov, in Combustion of
Energetic Materials, eds. K. K. Kuo and L. T. DeLuca, Begell House,
Inc., New York, 2002, p. 62.
3 V. V. Rozhkov, A. M. Kuvshinov, V. I. Gulevskaya, I. I. Chervin and
S. A. Shevelev, Synthesis, 1999, 2065.
4 E. Kuhle, Synthesis, 1970, 561.
5 A. Ruwet and M. Renson., Bull. Soc. Chim. Belg., 1970, 593.
This work was supported by the Russian Foundation for
Basic Research (project no. 01-03-32261).
†
General procedure. A mixture of trinitrostilbene 1 (0.01 mol), K2CO3
(0.01 mol) and benzylmercaptan (0.01 mol) in 20 ml of N-methyl-2-
pyrrolidone was stirred for 30 min at 20 °C with TLC monitoring. After
the reaction was complete, the mixture was poured into water. The
resulting precipitate was washed several times with water on a filter and
dried in air. The yields of 2 + 2' isomeric sulfide mixtures were 77%
(2a), 86% (2b), 82% (2c) and 54% (2d).
The non-separated mixture of isomeric sulfides 2 + 2' (0.01 mol) was
dissolved in 10 ml of dichloroethane, then SO2Cl2 was added (0.01 mol to
obtain benzothiophenes or 0.02 mol to obtain 3-chlorobenzothiophenes);
after the reaction was completed (~0.5 h, TLC monitoring), the reaction
mixture was concentrated and the resulting oil was recrystallised from
an ethanol–acetonitrile mixture (1:1).
The electron impact mass spectra of all the compounds synthesised
contained a molecular ion peak [MS-30 (Kratos)]. The 1H NMR spectra
were recorded in [2H6]DMSO on a Bruker AM-300 instrument. The
yields of the final thiophenes were calculated with respect to the pure
ortho-isomer.
2-Phenyl-4,6-dinitrobenzo[b]thiophene 5a: yield 66%; mp 214–215 °C.
4
4
1H NMR, d: 9.52 (d, 1H, H-7, J 1.9 Hz), 8.93 (d, 1H, H-5, J 1.9 Hz),
8.49 (s, 1H, H-3), 7.95 (m, 2H, Ph), 7.56 (m, 3H, Ph). Found (%): C,
58.73; H, 2.87; Cl, 9.77; N, 14.91. Calc. for C18H11ClN4O3 (%): C,
58.95; H, 3.05; Cl, 9.67; N, 15.28.
2-(4-Chlorophenyl)-4,6-dinitrobenzo[b]thiophene 5b: yield 71%,
4
mp 237–238 °C. 1H NMR, d: 9.50 (d, 1H, H-7, J 1.9 Hz), 8.91 (d, 1H,
4
3
H-5, J 1.9 Hz), 8.47 (s, 1H, H-3), 7.96 (d, 2H, 4-ClC6H4, J 7.6 Hz),
7.56 (d, 2H, 4-ClC6H4, 3J 7.6 Hz). Found (%): C, 55.79; H, 2.86; N,
8.89; S, 10.57. Calc. for C14H8N2O4S (%): C, 56.00; H, 2.69; N, 9.33;
S, 10.68.
2-(4-Methoxyphenyl)-4,6-dinitrobenzo[b]thiophene 5c: yield 52%,
4
mp 207–208 °C. 1H NMR, d: 9.43 (d, 1H, H-7, J 2.1 Hz), 8.87 (d, 1H,
H-5, 4J 2.1 Hz), 8.35 (s, 1H, H-3), 7.86 (d, 2H, 4-MeOC6H4, 3J 8.2 Hz),
7.10 (d, 2H, 4-MeOC6H4, 3J 8.2 Hz), 3.82 (s, 3H, MeO). Found (%): C,
54.32; H, 2.95; N, 8.23; S, 9.82. Calc. for C15H10N2O5S (%): C, 54.54;
H, 3.05; N, 8.48; S, 9.71.
2-(4-Trifluoromethylphenyl)-4,6-dinitrobenzo[b]thiophene 5d: yield
47%, mp 192–193 °C. 1H NMR, d: 9.54 (d, 1H, H-7, 4J 2.1 Hz), 8.96 (d,
1H, H-5, 4J 2.1 Hz), 8.61 (s, 1H, H-3), 8.18 (d, 2H, 4-CF3C6H4, 3J
3
8.2 Hz), 7.90 (d, 2H, 4-CF3C6H4, J 8.2 Hz). Found (%): C, 48.62; H,
1.76; N, 7.40; S, 8.89. Calc. for C15H7F3N2O4S (%): C, 48.92; H, 1.92;
N, 7.61; S, 8.71.
2-Phenyl-3-chloro-4,6-dinitrobenzo[b]thiophene 6a: yield 86%,
4
mp 154–155 °C. 1H NMR, d: 9.45 (d, 1H, H-7, J 2.0 Hz), 8.81 (d, 1H,
H-5, 4J 2.0 Hz), 7.77 (m, 2H, Ph), 7.60 (m, 3H, Ph). Found (%): C,
49.95; H, 2.24; Cl, 10.71; N, 8.07. Calc. for C14H7ClN2O4S (%): C,
50.23; H, 2.11; Cl, 10.59; N, 8.37.
2-(4-Chlorophenyl)-3-chloro-4,6-dinitrobenzo[b]thiophene 6b: yield
4
71%, mp 211–212 °C. 1H NMR, d: 9.48 (d, 1H, H-7, J 1.9 Hz), 8.82
(d, 1H, H-5, 4J 1.9 Hz), 7.79 (d, 2H, 4-ClC6H4, 3J 7.9 Hz), 7.66 (d, 2H,
4-ClC6H4, 3J 7.9 Hz). Found (%): C, 45.32; H, 1.42; Cl, 18.97; N, 7.26.
Calc. for C14H6Cl2N2O4S (%): C, 45.55; H, 1.64; Cl, 19.21; N, 7.59.
Received: 22nd October 2003; Com. 03/2185
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