Reaction of arendiazonium salts and SO2with α-nitroolefins

Article abstract of DOI:10.1023/B:RUJO.0000034940.16955.8e

In reaction of β-nitrostyrene and 2-(2-nitrovinyl)furan with arenediazonium chlorides and SO2 in the presence of copper(II) chloride products were obtained resulting from addition of arylsulfonyl group and a hydrogen atom across the C=C bond: 2-nitro-1-phenylethylsulfonylarenes and 2-(1-arylsulfonyl-2-nitroethyl)furans respectively. An anion-radical mechanism of the reaction was suggested.

Full text of DOI:10.1023/B:RUJO.0000034940.16955.8e

Russian Journal of Organic Chemistry, Vol. 40, No. 2, 2004, pp. 191-194. Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 2, 2004,
pp. 218-221.
Original Russian Text Copyright Ó 2004 by Bilaya, Obushak, Buchinskii, Ganushchak.
Reaction of Arendiazonium Salts and SO2
with a-Nitroolefins
E. E. Bilaya, N. D. Obushak, A. M. Buchinskii, and N. I. Ganushchak
Ivan Franko Lviv National University, L’viv, 79005 Ukraine
e-mail: obushak@in.lviv.ua
Received February 21, 2003
Abstract—In reaction of b-nitrostyrene and 2-(2-nitrovinyl)furan with arenediazonium chlorides and SO2 in the
presence of copper(II) chloride products were obtained resulting from addition of arylsulfonyl group and a
hydrogen atom across the C=C bond: 2-nitro-1-phenylethylsulfonylarenes and 2-(1-arylsulfonyl-2-nitroethyl)furans
respectively. An anion-radical mechanism of the reaction was suggested.
detail the reaction of a-nitroolefins with arenediazonium
chlorides and SO2.
Unsaturated compounds react with arenediazonium
chlorides and sulfur(IV) oxide under catalysis with
copper salts [1–11]. The reaction was shown to afford
a product of arylsulfonyl group and nucleophile addition
across the double bond 1–8] or to involve a replacement
by arylsulfonyl group of hydrogen, halogen, or carboxy
group [7–11]. The part of nucleophiles play in these
reactions chloride [1, 3, 4], bromide [3, 4], thiocyanate-
[2, 4], xanthate, and diethyldithiophosphate ions [3, 4],
and also a hydroxy group [5–8]. The route taken by the
reaction depends on the character of the unsaturated
compound. The strong electron-acceptor substituents at
the double bond change the character of the reaction
[12, 13]. In the present study we investigated in more
We established that b-nitrostyrene I and 2-(2-
nitrovinyl)furan II reacted with the diazonium salts and
SO2 in the presence of copper(II) chloride as catalyst in a
mixture water–acetone–acetic acid to furnish products of
arylsulfonyl group and hydrogen atom addition at the double
bond, compounds IVa–IVf, Va Vb(Tables 1 and 2).
We failed to detect unsaturated sulfones and products
of arylsulfonyl group and chlorine addition to the double
bond that should be expected to be present basing on
results of [1–11]. The degree of monomer conversion
attained 45–60%.Arenesulfonyl chlorides formed beside
compounds IVa–IVf, Va, Vb in 40–60% yield.
Table 1. Yields, melting pointsa, and elemental analyses of (2-nitro-1-phenylethyl)sulfonylarenes IVa–f and 2-(1-arylsulfonyl-2-
nitroethyl)furans Va, b
)RXQGꢀꢁꢂꢁ
&DOFXODWHGꢀꢁꢂꢁ
&RPSGꢃꢁ <LHOGꢀꢁ PSꢀꢁ
)RUPXODꢁ
QRꢃꢁꢁ
ꢂꢁꢁ
ꢁꢁ
&ꢁ
+ꢁ
1ꢁꢄ%Uꢅꢁ
ꢍꢃꢋꢉꢁ
ꢍꢃꢇꢍꢁ
ꢍꢃꢊꢏꢁ
ꢍꢃꢏꢉꢁ
6ꢁ
&ꢁ
+ꢁ
1ꢁꢄ%Uꢅꢁ
ꢍꢃꢉꢈꢁ
ꢍꢃꢇꢌꢁ
ꢍꢃꢇꢌꢁ
ꢍꢃꢆꢊꢁ
6ꢁ
,9Dꢀ
,9Eꢀ
,9Fꢀ
ꢆꢇꢁ ꢈꢉꢊ±ꢈꢉꢋꢁ ꢇꢋꢃꢊꢌꢁ ꢍꢃꢊꢈꢁ
ꢆꢈꢁ ꢈꢈꢎ±ꢈꢈꢏꢁ ꢇꢉꢃꢋꢉꢁ ꢇꢃꢎꢏꢁ
ꢈꢈꢃꢎꢍꢁ & + 12 6ꢁ
ꢈꢎꢃꢇꢇꢁ & + 12 6ꢁ
ꢈꢎꢃꢍꢉꢁ & + 12 6ꢁ
ꢈꢎꢃꢎꢈꢁ & + 12 6ꢁ
ꢇꢋꢃꢋꢏꢁ ꢍꢃꢇꢎꢁ
ꢇꢌꢃꢎꢎꢁ ꢍꢃꢌꢇꢁ
ꢇꢌꢃꢎꢎꢁ ꢍꢃꢌꢇꢁ
ꢇꢊꢃꢎꢊꢁ ꢍꢃꢋꢎꢁ
ꢈꢈꢃꢎꢈꢁ
ꢈꢎꢃꢇꢎꢁ
ꢈꢎꢃꢇꢎꢁ
ꢍꢆꢁ
ꢈꢍꢉꢁ
ꢇꢉꢃꢌꢎꢁ ꢍꢃꢉꢏꢁ
,9Gꢀ
,9Hꢀ
ꢆꢎꢁ
ꢏꢍꢁ
ꢈꢍꢇꢁ
ꢈꢍꢆꢁ
ꢇꢇꢃꢉꢉꢁ ꢍꢃꢇꢌꢁ
ꢍꢇꢃꢆꢋꢁ ꢆꢃꢆꢈꢁ
ꢌꢃꢌꢉꢁ
ꢉꢃꢊꢊꢁ
ꢆꢃꢊꢏꢁ
ꢉꢃꢍꢋꢁꢁ & + %U12 6ꢁ ꢍꢇꢃꢍꢏꢁ ꢆꢃꢏꢋꢁ
ꢆꢃꢋꢉꢁ
ꢄꢏꢈꢃꢊꢆꢅꢁ
ꢄꢏꢈꢃꢇꢉꢅꢁ
,9Iꢀ
9 ꢀ
9Eꢀ
ꢍꢇꢁ
ꢈꢇꢍꢁ
ꢍꢌꢃꢉꢉꢁ ꢆꢃꢍꢌꢁ
ꢉꢃꢆꢉꢁ
ꢍꢃꢊꢎꢁ
ꢉꢃꢊꢎꢁ
ꢌꢃꢍꢍꢁ & + 1 2 6ꢁ ꢇꢎꢃꢎꢎꢁ ꢆꢃꢊꢎꢁ
ꢉꢃꢆꢆꢁ
ꢍꢃꢋꢍꢁ
ꢉꢃꢇꢌꢁ
ꢌꢃꢇꢆꢁ
ꢈꢎꢃꢉꢊꢁ
ꢌꢃꢉꢆꢁ
ꢏꢋꢁ ꢈꢏꢌ±ꢈꢆꢎꢁ ꢇꢏꢃꢉꢇꢁ ꢍꢃꢊꢈꢁ
ꢏꢊꢁ ꢈꢇꢈ±ꢈꢇꢏꢁ ꢍꢍꢃꢎꢇꢁ ꢆꢃꢎꢏꢁ
ꢈꢎꢃꢋꢏꢁ & + 12 6ꢁ
ꢇꢏꢃꢉꢋꢁ ꢍꢃꢍꢍꢁ
ꢌꢃꢋꢎꢁ & + 1 2 6ꢁ ꢍꢍꢃꢈꢋꢁ ꢆꢃꢎꢌꢁ
a
ꢁ
mp, °C: IVa, 186–187 [14]; IVc, 147.5–148 [14]; IVf, 148–150 [15].
1070-4280/04/4002-0191Ó2004 MAIK “Nauka/Interperiodica”

192
BILAYA et al.
Table 2. 1H NMR spectra of sulfones IVa–f and Va, b, d, ppm (J, Hz)
&RPSGꢀꢁꢁ
QRꢀꢁ
ꢁ
ꢁ
5ꢁꢂVꢃꢁꢄ ꢅꢁ
;ꢁ
62
ꢁ
,9Eꢀ
ꢆꢀꢇꢈ±ꢆꢀꢉꢊꢁPꢁꢂꢇ+ꢅꢁ
ꢆꢀꢆꢋꢁGꢀGꢁꢂꢋ+ꢅꢃꢁꢁ ꢇꢀꢆꢇꢁ ꢈꢀꢄꢊ±ꢈꢀꢉꢄꢁPꢁꢂꢈ ꢅꢃꢁꢈꢀꢆꢈ±ꢈꢀꢌꢍꢁPꢁ ꢁ
-ꢁꢋꢄꢀꢆꢃꢁ -ꢁꢆꢀꢉꢁ
ꢂꢇ ꢅꢁꢁ
,9Fꢀ
,9Gꢀ
,9Hꢀ
,9Iꢀ
9Dꢀ
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ꢆꢀꢇꢄ±ꢆꢀꢄꢆꢁPꢁꢂꢇ+ꢅꢁ
ꢆꢀꢉꢊ±ꢆꢀꢉꢍꢁPꢁꢂꢇ ꢅꢁ
ꢆꢀꢄꢉ±ꢆꢀꢌꢇꢁPꢁꢂꢄ ꢅꢁꢁ
ꢁ
ꢇꢀꢉꢇꢁ ꢈꢀꢇꢈ±ꢈꢀꢄꢌꢁPꢁꢂꢆ ꢅꢁ
ꢈꢀꢄꢈꢁGꢁꢂꢇ ꢅꢃꢁꢈꢀꢆꢄꢁGꢁ
ꢂꢇ ꢅꢁ
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ꢂꢇ ꢅꢁ
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ꢂꢇ ꢅꢁ
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ꢂꢇ ꢅꢁ
ꢆꢀꢉꢈꢁGꢀGꢁꢂꢋ+ꢅꢃꢁꢁ ꢄꢀꢎꢊꢁ ꢈꢀꢄꢊ±ꢈꢀꢉꢊꢁPꢁꢂꢆ ꢅꢁ
-ꢁꢋꢇꢀꢎꢃꢁ -ꢁꢉꢀꢇꢁ
ꢆꢀꢆꢈꢁGꢀGꢁꢂꢋ+ꢅꢃꢁꢁ
ꢁ
ꢁ
ꢈꢀꢄꢇ±ꢈꢀꢉꢄꢁPꢁꢂꢆ ꢅꢁ
ꢈꢀꢄꢇ±ꢈꢀꢉꢄꢁPꢁꢂꢆ ꢅꢁ
-ꢁꢍꢀꢋꢃꢁ -ꢁꢆꢀꢈꢁ
ꢁ
ꢆꢀꢇꢈꢁGꢀGꢁꢂꢋ ꢃꢁ -ꢁꢋꢉꢀꢈꢃꢁꢁ
-ꢁꢋꢊꢀꢊꢅꢃꢁꢆꢀꢄꢆꢁGꢀGꢁꢂꢋ+ꢃꢁ -ꢁꢆꢀꢈꢅꢁ
ꢆꢀꢄꢌꢁGꢀGꢁꢂꢋ ꢃꢁ -ꢁꢋꢆꢀꢊꢃꢁꢁ
ꢆꢀꢌꢄꢁGꢀGꢁꢂꢋ+ꢅꢁꢁ ꢇꢀꢄꢈꢁ ꢌꢀꢉꢆꢁPꢁꢂꢋ ꢃꢁꢉꢏ ꢅꢃꢁꢌꢀꢆꢋꢁGꢁꢂꢋ ꢃꢁ ꢈꢀꢉꢋ±ꢈꢀꢆꢆꢁPꢁꢂꢄ ꢅꢃꢁ
ꢄꢏ ꢅꢃꢁꢈꢀꢌꢉꢁEUꢀVꢁꢂꢋ ꢃꢁꢆꢏ ꢅꢁ ꢈꢀꢆꢎꢁGꢁꢂꢋ ꢅꢁ
ꢌꢀꢉꢈꢁPꢁꢂꢋ ꢃꢁꢉꢏ ꢅꢃꢁꢌꢀꢆꢍꢁGꢁꢂꢋ ꢃꢁ ꢈꢀꢎꢍꢁGꢁꢂꢇ ꢅꢃꢁꢍꢀꢉꢇꢁGꢁ
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9Eꢀ
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ꢁ
Besides copper(II)chloride the reaction is catalyzed
Arylsulfonyl group enters into the a-position with
respect to the aromatic group of alkene (in contrast to
the cases described in [1–11]) and into the b-position
with respect to the acceptor substituents. The
by copper(II) acetate. Both catalysts ensure comparable
yields of compounds IVa–g, Va, b, whereas these
sulfones do not form in the absence of catalysts.
$U62 &Oꢀꢀꢁꢀꢀ62 ꢀꢀꢁꢀꢀ+ 2
9,D J
$U62 +ꢀꢀꢁꢀꢀ+&Oꢀꢀꢁꢀꢀ+ 62
12
ꢀꢁꢁ62 ꢁꢁꢀꢁꢁ5& + 1 &O
;
,ꢀꢁ,,
,,,D J
regiodirection of reaction corresponds to that of formation
of products at the sulfinic acids nucleophilic addition
across a double bond [14–17].Actually, arenesulfinic acids
may arise in the course of the reaction by reduction of
arenesulfonyl chlorides by the following scheme [18]:
;
&X ꢂ&X
2 1
2
6
& + 5
2
,9D Iꢀꢁ9DꢀꢁE
&X
X = Ph (I, IV), 2-furyl (II, V); III, IV, R = H (a), 2-Me (b),
4-Me (c), 4-MeO (d), 4-Br (e), 4-NO2 (f), 3-Me (g); V, R =
3-Me (a), 4-NO2 (b).
,ꢀꢀꢁꢀꢀꢃꢄ0H& + 62 &O
,9F
RUꢀ&X
9,,,
We established however, that compound IVc formed
also in reaction of olefine I with p-toluenesulfonyl chloride
VII in the presence of CuCl2 (or CuCl).
&X
62 ꢀꢀꢁꢀꢀ5& + 1 ꢀ&O
$U62 &Oꢀꢀꢁꢀꢀ1
&X
,,,D J
9,D J
–
The formation of an anionArSO2 under conditions of
In reaction of benzyldiazonium chloride IIIa with 2-
(2-nitrovinyl)furan II alongside compound Va formed also
a product of arylsulfonylation in the position 5 of furan
ring VII.
this reaction is hardly probable. It is known that alkyl-
(or aryl)sufonyl radicals form here [19] and not sulfanate
anions. Besides the capability of arenesulfinate anion to
be involved in the nucleophilic addition as S- or O-alkyl-
ating agent also should be taken in consideration. In this
case the less sterically strained compound would be the
sulfinic acid ester that we have not detected among the
reaction products. In the reactions with sodium
benzenesulfinate an ion-radical mechanism is operative
[20]. Besides the copper salts are active promoters of
ion-radical processes [21–25].
12 ꢀꢀꢁꢀꢀ62 ꢀꢀꢁꢀꢀ3K1 ꢀ&O
2
,,
ꢁ
&X ꢂ&X
3K62
12
2
12
62 3K
2
9F
9,,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 2 2004

193
REACTION OF ARENDIAZONIUM SALTS
Hence in the reaction under study of alkenes and
dienes with arenediazonium salts and SO2 occurred the
addition of an arylsulfonyl group and a hydrogen atom in
contrast to the previously described addition of an
arylsulfonyl group and a nucleophile [1–8]. This difference
is apparently due to the fact that for the electron-deficient
nitroolefins the anion-radical state is more stable than
cation-radical one [26–28].
The anion-radical mechanism of a reaction between
an electron-deficient olefin (b,c,c-trifluorostyrene) and
arenediazonium salts was substantiated in [29].
Besides the one-electron transfer to form ion-radicals
is also characteristic of the arendiazonium cations [18,
25, 30, 31]. Taking into account these data and our
experimental results the following scheme may be
suggested:
;
12
&X
&X
&X
;
;
62
$U1
$U
12
62
&X
122
62
$U62
$U1
;
122
$U62
12
62 $U
1
;
+6RO
62 $U
6RO
It is therefore presumable that olefins with strong
electron-withdrawing substituents at the double bond
react with arenediazonium salts and SO2 according to
the mechanism of anion-radical addition [29].
IVe, f and Va, b) substance was washed with water,
hexane, or petroleum ether, and recrystallized from
ethanol. Thus were obtained compounds IVa–f, Va, b.
On evaporation of the remaining filtrate arenesufonyl
chlorides VIa–g were isolated.
EXPERIMENTAL
In reaction between benzenediazonium chloride IIIa
with 2-(2-nitrovinyl)furan II were obtained compounds
Va and VII in 18 and 12% yield respectively. 1H NMR
1H NMR spectra of compounds IV and V were
registered on a spectrometer Varian VXR-300 (300 MHz)
in CD3COCD3 (IVb–f)or DMSO-d6 (Va–c), internal
2
spectrum, d, ppm: 5.29 d.d (Va; 0.6 H, CH2, J 14,
reference HMDS
.
3J 8 Hz), 5.38 d.d (Va; 0.6 H, CH2, 3J 5.3 Hz), 5.68 d.d
(Va; 0.6 H, CH), 6.44 m (Va; 0.6 H, H4 of furan), 6.49 d
(Va; 0.6 H, H3 of furan, J 3.0 Hz), 6.77 br.s (VII; 0.4 H,
H3 of furan), 7.28 d (VII; 0.4 H, H4 of furan., J 3.4 Hz),
7.55–7.82 m (Va + VII; 5.6 H, C6H5, CH=CH, H5 of
furan.), 7.99–8.06 m (VII; 0.8 H, C6H5). The integral
intensities of signals and elemental analysis indicate that
the ratio of compounds Va and VII is equal to 3:2.
Reaction of arenediazonium chlorides and SO2
with compounds I and II. To a mixture of 50 ml of
acetone and 50 ml of acetic acid saturated with
sulfur(IV) oxide was added 4 g of CuCl2·2H2O and 0.1
mol of compound I or II. The mixture was stirred at 15–
20°C while a water solution of arenediazonium chloride
IIIa–g prepared by diazotization of.1 mol of an ap-
propriate amine was gradually added. The reaction was
continued till the nitrogen evolution stopped. Then the
reaction mixture was diluted with 300–500 ml of water.
The separated oily or crystalline ( in case of compounds
Reaction of p-toluenesulfonyl chloride with c-
nitrostyrene. To a solution of 19 g (0.1 mol) of p-tolu-
enesulfonyl chloride VIII and 14.9 g (0.1 mol) of b-nitro-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 2 2004

194
BILAYA et al.
14. Cason, L.F. and Wanser, C.C., J. Am. Chem. Soc., 1951,
vol. 73, p. 142.
15. Messinger, P., Arch. Pharm., 1973, vol. 306, p. 458.
16. Achmatowicz, O. and Michalski, J., Roczn. Chem., 1956,
vol. 30, p. 243.
17. Obushak, M., Bila, E., Matiichuk, V., and Ganushchak,. Visnik
L’viv. Universitetu, Ser.Khim., 2002, vol. 41, p. 167.
18. Saunders, K.H. and Allen, R.L.M., Aromatic, Diazo,
Compounds, London: Edward,Arnold, 1985, p. 726.
19. Tanaskov, M.M. and Stadnichuk, M.D., Zh. Obshch. Khim.,
1978, vol. 48, p. 1140.
20. Todres, Z.V., Ion-radikaly v organicheskom sinteze (Ion
Radicals in Organic Synthesis), Moscow: Khimiya, 1986,
p. 149.
21. Bowman, W.R., Heaney, H., and Smith, P.H.G., Tetrahedron
Lett., 1984, vol. 25, p. 5821.
22. Liedholm, B., Acta Chem. Scand. B, 1984, vol. 38, p. 877.
23. Bilaya, E.E., Cand. Sci. (Chem.) Dissertation, L’vov, 1989.
24. Bila, E.E., Obushak, M.D., and Ganushchak, M.I., Pol.
J. Chem., 2000, vol. 74, p. 1567.
styrene I in 50 ml of acetone was added 4 g of
CuCl2·2H2O (or 3 g of CuCl), and the mixture was vigor-
ously stirred at 20–25°C for 10 h. Isolation and purifica-
tion of the product obtained was done as described above.
Compound IVc was obtained in 25% yield.
REFERENCES
1. Naidan, V.M., Naidan, G.D., and Litvin, G.V., Zh. Org. Khim.,
1978, vol. 14, p. 2622.
2. Naidan, V.M., Naidan, G.D., and Dombrovskii, A.V., Zh.
Obshch. Khim., 1979, vol. 49, p. 1829.
3. Naidan, V.M. and Naidan, G.D., Zh. Obshch. Khim., 1980,
vol. 50, p. 2611.
4. Naidan, V.M., Naidan, G.D., Drozdova, S.G., and Musien-
ko, V.M., Zh. Obshch. Khim., 1985, vol. 55, p. 391.
5. Bilaya, E.E., Obushak, N.D., and Ganushchak, N.I., Zh. Org.
Khim., 1999, vol. 35, p. 655.
6. Bila, A. and Ganushchak, M., and Obushak, M., Visnik
L’viv. Universitetu, Ser. Khim., 2001, vol. 40, p. 173.
7. Bilaya, E.E., Obushak, N.D., Ganushchak, N.I., and
Buchinskii,A.M., Zh. Org. Khim. , 1996, vol. 32, p. 1528.
8. Bila, E.E. and Obushak, M.D., Visnik L’viv. Universitetu,
Ser. Khim., 1995, vol. 35, p. 74.
9. Obushak, N.D., Bilaya, E.E., and Ganushchak, N.I., Zh. Org.
Khim. , 1991, vol. 27, p. 2372.
10. Bila, E., Ganushchak, M., and Obushak, M., Visnik L’viv.
Universitetu, Ser. Khim., 2001, vol. 40, p. 176.
11. Bila, E. and Ganushchak, M. , Visnik L’viv. Universitetu,
Ser. Khim., 2000, vol. 39, p. 256.
25. Obushak, N.D., Lyakhovich, M.B., and Bilaya, E.E., Zh. Org.
Khim., 2002, vol. 38, p. 47.
26. Todres, Z.V., Nekrasova, G.V., Lipina, E.S., and Chernysho-
va, T.M., Izv. Akad. Nauk, SSSR, Ser.Khim., 1979, p. 126.
27. Todres, Z.V., Kuryaeva, T.T., Ryzhova, G.L., and Kursa-
nov, D.N., Izv. Akad. Nauk SSSR, Ser. Khim., 1980, p. 1602.
28. Shvekhgeimer, G.A., Zvolinskii, V.I., Kobrakov, K.I., and
Bargamov, G.G., Dokl. Akad. Nauk SSSR., 1984, vol. 278,
p. 888.
29. Bilaya, E.E., Obushak, N.D., and Ganushchak, N.I., Zh. Org.
Khim. , 1997, vol. 33, p. 1068.
30. Singh, P.R. and Kumar, P., Austr. J. Chem., 1972, vol. 25,
p. 2133.
12. Buchins’kii, A.M., Obushak, N.D., and Bila, E.E., Visnik
L’viv. Universitetu, Ser. Khim., 1997, vol. 37, p. 86.
13. Obushak, N.D., Buchinskii, A.M., Bilaya, E.E., and Ganu-
shchak, N.I., Zh. Obshch. Khim., 1997, vol. 67, p. 1405.
31. Singh, P.R. and Kumar, P., Tetrahedron Lett., 1972, p. 613.
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