Furazan ring opening upon treatment of benzofurazan with ethanolamine to yield quinoxalines

Article abstract of DOI:10.1007/s11172-007-0400-x

Heating of benzofurazans with ethanolamine in the presence of catalytic amount of p-toluenesulfonic acid leads to quinoxalines.

Full text of DOI:10.1007/s11172-007-0400-x

Russian Chemical Bulletin, International Edition, Vol. 56, No. 12, pp. 2510—2512, December, 2007
2510
Furazan ring opening upon treatment of benzofurazan
with ethanolаmine to yield quinoxalines
V. A. Samsonov
N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry,
Siberian Branch of the Russian Academy of Sciences,
9 prosp. Akad. Lavrentґeva, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383) 330 9752. Eꢀmail: Samson@nioch.nsc.ru
Heating of benzofurazans with ethanolamine in the presence of catalytic amount of
pꢀtoluenesulfonic acid leads to quinoxalines.
Key words: benzofurazans, ethanolаmine, quinoxalines.
Scheme 2
Study of chemical properties of benzofurazans showed
that the heating of compounds 1a—g with ethanolamine
at 150—170 °C in the presence of catalytic amount of
pꢀtoluenesulfonic acid unexpectedly leads to quinoxalines
2a—g (Scheme 1).
Scheme 1
1, 2: R1 = H, R2 = H (a), Me (b), MeO (c); R1 = NH2, R2 = H (d);
N
N
Ph
R
1 + R2
=
(e),
(f), —CH=CH—CH=CH—
N
heat and leads to furazano[4,5ꢀf]quinoxaline 2e in 76%
yield. Upon further heating of compound 2e with ethanolꢀ
amine at 150 °C, a reduction of its furazan ring takes
place to form 5,6ꢀdiaminoquinoxaline 3 (Scheme 2).
(g)
It should be noted that the reaction of benꢀ
zo[1,2ꢀc:3,4ꢀc´]difurazan 1e proceeds with generation of
Scheme 3
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2424—2425, December, 2007.
1066ꢀ5285/07/5612ꢀ2510 © 2007 Springer Science+Business Media, Inc.

Formation of quinoxalines
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 12, December, 2007 2511
Table 1. Conditions of the reaction and yields of quinoxalines
Apparently, ethanolаmine plays the role of a reducing
agent similarly to ethylenediamine, which is a mild reꢀ
ducing agent.1
Starting
comꢀ
T/°С
τ/h
Proꢀ YIeld
duct (%)
M.p./°С
(lit. data)
The sequence of processes in this synthesis of quinoxꢀ
aline derivatives is not yet studied. It can be supposed that
the enamine is initially formed from ethanolаmine. Conꢀ
version of ethanolamines to enamines upon treatment
with acids was confirmed in Ref. 2. Further attack of
enаmine at the nitrogen atom of the furazan ring leads to
the ring opening followed by the pyrazine ring closure to
form quinoxaline Nꢀoxide similarly to the known "Beirut
reaction".3 NꢀOxide oxygen atom, apparently, is readily
eliminated upon treatment with ethanolаmine, which, as
it was shown above, is a reducing agent (Scheme 3).
The found way for the synthesis of quinoxalines from
benzofurazans can serve as the alternative to the already
existing methods.
pound
1a
1b
1c
1d
1e
1f
150—160
150—160
150—160
165—170
100—120
150—160
165—170
150—160
4
5
4
12
1
4
2a
2b
2c
2d
2e
2f
87
85
72
74
75
89
78
29—30 (30.5)12
Oil (b.p. 248)13
55—57 (57.5)13
93—95 (90)14—16
164—165 *
194—195 *
1g
2e
16
1
2g
3
54—56 (55—57)1
66 144—145 (144—145)12
* Compounds were rеcrystallized from ethanol.
J = 2 Hz). 13C NMR, δ: 149.09; 147.84; 146.94 (CH); 146.02;
144.95 (CH); 135.90; 134.58 (CH); 118.31 (CH).
2ꢀPhenylꢀ2Hꢀtriazolo[4,5ꢀf]quinoxaline (2f). Found (%):
C, 67.90; H, 3.65; N, 28.20. C14H9N5. Calculated (%): C, 68.00;
H, 3.67; N, 28.33. MS, m/z: 247 [M]+. 1H NMR, δ: 7.38 (m,
1 H, Рh); 7.48 (m, 2 H, Ph); 7.85, 8.03 (both d, 1 H each, J =
10 Hz); 8.36 (m, 2 H, Ph); 8.84, 8.86 (both d, 1 H each, J =
2 Hz). 13C NMR, δ: 144.91; 144.56 (CH); 144.07; 143.83 (CH);
141.65; 139.80; 137.76; 129.46 (CH); 129.27 (CH); 128.93 (CH);
121.27 (CH); 120.22 (CH).
Experimental
IR spectra were recorded on a Bruker Vector spectrometer
in KBr pellets (concentration, 0.25%), H and 13C NMR specꢀ
1
tra were recorded on a Bruker AM 400 spectrometer (400.13 and
100.63 MHz, respectively) as 5—10% solutions in CDCl3, sigꢀ
nals of residual protons of the solvent at δ 7.24 (1H) and 76.90
(
13C) relatively to Ме4Si were used as the internal standard.
Mass spectra were recorded on a Finnigan MATꢀ8200 instruꢀ
ment (ionization energy of electrons: 70 eV, direct inlet of a
substance, the source of ions temperature: 180 °C). Monitoring
of the course of the reaction and purity of compounds were
performed by TLC on Sorbfil UVꢀ254 plates with visualization
in the UV light. Melting points were determined on the Kofler
microheating stage.
Benzofurazans 1a,b,e were synthesized according to the proꢀ
cedures described earlier4—6 from the corresponding benzofuroxꢀ
ans by the reaction with triethyl phosphite. Compounds 1c,7
1d,8 and 1f 9 were obtained according to the known procedures.
Compound 1g was synthesized from the corresponding dioxime
by its oxidation to furoxan10 followed by the reduction to furaꢀ
zan with sulfur in ethylene glycol11 in 60% yield. Structures of
quinoxalines obtained were established by comparison of their
melting points, IR and NMR spectra with those published in the
literature.
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Ethanolаmine (4 mL) and pꢀtoluenesulfonic acid (0.1 g) were
added to benzofurazan 1a—g or 2g (1 g). The mixture was heatꢀ
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Received August 29, 2007