Oxidative devinylation of N-vinylpyrroles

Full text of DOI:10.1134/S1070428008080277

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 8, pp. 1247–1248. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © B.A. Trofimov, E.Yu. Shmidt, A.I. Mikhaleva, N.V. Zorina, E.Yu. Senotrusova, 2008, published in Zhurnal Organicheskoi Khimii,
2
008, Vol. 44, No. 8, pp. 1258–1259.
SHORT
COMMUNICATIONS
Oxidative Devinylation of N-Vinylpyrroles
B. A. Trofimov, E. Yu. Shmidt, A. I. Mikhaleva, N. V. Zorina, and E. Yu. Senotrusova
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: boris_trofimov@irioch.irk.ru
Received January 19, 2008
DOI: 10.1134/S1070428008080277
N-Vinylpyrroles are reactive building blocks for the
synthesis of various compounds of the pyrrole series
of the pyrrole ring on treatment with a dilute (0.4–
2.0%) aqueous solution of potassium permanganate
over a period of a few minutes. The reactions occurred
at –20 to 20°C, and the yield (unoptimized) of the cor-
responding NH-pyrroles was 22–24%. The efficiency
of the process depends on the structure of the initial
N-vinylpyrrole. For example, only traces of the corre-
sponding NH derivative were obtained from N-vinyl-
[
[
1–7], medical agents [8, 9], pesticides [10], repellents
11], epoxy resins [12], light-sensitive [13, 14] and
semiconducting polymers [15], and materials for opto-
electronics [6, 16]. N-Vinylazoles (including N-vinyl-
pyrroles) are used as azoles with protected NH func-
tionality in a number of important syntheses, in partic-
ular in the preparation of antiphlogistic drugs [17].
Removal of the vinyl protection can be achieved by
hydrolysis [18], mercuration followed by reduction
1
4,5,6,7-tetrahydroindole (according to the H NMR
data), though the substrate was consumed completely.
Obviously, in this case successful devinylation requires
even milder conditions (lower temperature, shorter
time, and smaller oxidant concentration).
Our attempts to perform devinylation in a hetero-
geneous system (benzene, diethyl ether, 2% KMnO4,
room temperature), as well as in an aqueous dispersion
with NaBH [19] (N-vinylpyrroles), ozonolysis [20]
4
(
(
N-vinylimidazoles), and oxidation with KMnO [21]
N-vinylpyrazoles). From the preparative viewpoint,
4
the most attractive is oxidative elimination of the
N-vinyl group by the action of potassium permanga-
nate, which was recently described for di- and tri-
bromo-N-vinylpyrazoles [21].
(1% KMnO ) were unsuccessful: 70–94% of the initial
4
N-vinylpyrrole was recovered from the reaction mix-
ture. Nevertheless, it is obvious that further optimiza-
tion could lead to the development of a convenient
express procedure for devinylation of N-vinylpyrroles.
Devinylation of N-vinylpyrroles involves the
strongest difficulties due to high reactivity of pyrrole
ring toward oxidants and electrophiles. Therefore, it
seemed to be very important to elucidate whether de-
Devinylation of 2-phenyl-1-vinyl-1H-pyrrole
(
2
(
Ia). A solution of 0.2 g (1.18 mmol) of pyrrole Ia in
0 ml of acetone was cooled to –20°C, and 0.56 g
3.55 mmol) of a freshly prepared 2% aqueous solution
vinylation of N-vinylpyrroles with KMnO is possible,
4
taking into account that the known ability of pyrrole
ring to undergo oxidation [22] could give rise to unde-
sirable side processes.
of potassium permanganate was added under stirring.
The mixture turned colorless within 5 min, and MnO2
separated as an amorphous material. The mixture was
diluted with 15 ml of water and extracted with diethyl
ether (3×15 ml), the combined extracts were washed
with water (3×15 ml) and dried over potassium carbo-
nate, and the solvent was removed to leave 0.04 g
Our experiments showed that some N-vinylpyrroles
are capable of losing the vinyl group with conservation
0
.4–2.0% KMnO4
acetone–H O, 5 min
2
R
R
N
N
H
2
2–24%
(
24%) of pyrrole IIa whose physical constants were
CH2
consistent with published data [2].
Ia, Ib
IIa, IIb
Devinylation of 2-(2-naphthyl)-1-vinyl-1H-pyr-
role (Ib). A freshly prepared 2% aqueous solution of
R = Ph (a), 2-naphthyl (b).
1
247

1
248
TROFIMOV et al.
potassium permanganate, 0.43 g (2.73 mmol) was
added to a solution of 0.2 g (0.91 mmol) of pyrrole Ib
in 10 ml of acetone under stirring at room temperature.
The mixture turned colorless within 5 min, the precip-
9. Zhavrid, S.V., Shashikhina, M.N., Gribkova, N.V.,
Kazak, N.F., Mikhaleva, A.I., Trofimov, B.A., Vasil’-
ev, A.N., Zhungietu, G.I., Rekhter, M.A., Radul, O.M.,
Vlad, L.A., Bukhanyuk, S.M., and Zorin, L.M., Khim.-
Farm. Zh., 1983, p. 25.
itate of MnO was filtered off and washed with acetone
2
1
0. Morozova, L.V., Mikhaleva, A.I., Markova, M.V., Mol-
chanov, O.Yu., and Putan, T.V., Khimiya i primenenie
pestitsidov (Chemistry and Application of Pesticides),
Moscow, 1990, p. 7.
(
3×5 ml), acetone was removed from the filtrate, and
the aqueous solution was extracted with ethyl acetate
3×10 ml). The extract was washed with water (3×
0 ml) and dried over potassium carbonate, and the
(
1
1
1. Massel’, G.I., Rozhkov, A.S., Mikhaleva, A.I., Vasil’-
solvent was distilled off to obtain 0.04 g (22%) of
pyrrole IIb. The physical constants of the product were
in agreement with published data [2].
ev, A.N., and Trofimov, B.A., Lesnoi Zh., 1984, p. 94.
1
2. Minakova, T.T., Morozova, L.V., Usmanova, T.A., Mi-
khaleva, A.I., and Trofimov, B.A., USSR Inventor’s
Certificate no. 653269, 1979; Ref. Zh., Khim., 1980,
no. 4S324P.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 06-03-08051-ofi) and by the Foundation for Sup-
port of Russian Science.
13. Morozova, L.V., Mikhaleva, A.I., Korostova, S.E., and
Filimonova, I.L., Elektronika organicheskikh materialov
(
Electronics of Organic Materials), Moscow: Nauka,
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 8 2008