ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 7, pp. 1087−1088. © ©Pleiades Publishing, Ltd., 2008.
Original Russian Text © ©B.F. Kukharev, V.K. Stankevich, V.A. Kukhareva, 2008, published in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 7, pp. 1096−
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097.
SHORT
COMMUNICATIONS
Iodine-Catalyzed Ketazines Cyclization into 2-Pyrazolines
B. F. Kukharev, V. K. Stankevich, and V. A. Kukhareva
Faworsky Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences,
Irkutsk, 664033 Russia
e-mail: irk_inst_chem@irioch.irk.ru
Received February 14, 2008
DOI: 10.1134/S1070428008070257
Ketazines are known to undergo cyclization into
-pyrazolines under the action of protonic acids.
3,5,5-trimethylpyrazoline (IIa). The pyrazoline was
isolated by distillation in 94% yield. Compare the acetone
azine cyclization with anhydrous oxalic acid at azine to
acid molar ratio 1:1.1: After 4-hour heating on a water
bath the pyrazoline forms in 78% yield [2].
2
Dicarboxylic acids are considered to be the most active
catalysts for ketazines cyclization [1, 2]. The reaction is
performed in the presence of an equimolar amount of
the acid and often requires additional heating. The
pyrazoline forms not in the form of a base but as a pyr-
azolinium salt of the corresponding acid, therefore the
reaction mixture should be treated with strong bases.
Yield of pyrazolines reaches from 50 to 81% [2].
It is presumable that initially forms a complex of azine
with iodine A where (same as in the catalysis with acids)
because of a positive charge arising on the nitrogen the
intramolecular condensation of crotonic type is facilitated
and leads to a complex pyrazoline–iodine B, which
reacting with azine Ia provides the base pyrazoline IIa
and the azine complex with iodine A.
We found that by adding to acetone azine (Ia)
.5 wt% of crystalline iodine a strong self-heating was
0
observed (to 125–130°C), and after maintaining the
reaction mixture at this temperature for 1 h the GLC
analysis showed a complete conversion of the azine into
Evidently since the iodine unlike the proton is a mild
acid [3] the equilibrium (2) is more shifted to the right
than the similar equilibrium involving the protonated
azine and pyrazoline. This event provides for the reaction
proceeding in the presence of the catalytical quantity of
iodine.
3,5,5-trimethyl-2-pyrazoline (IIa).To 11.22 g (0.1 mol)
of acetone azine (Ia) was added at room temperature
while stirring 0.05 g (0.2 mmol) of I . The reaction mix-
2
A
ture self-heated to 125–130°C and was kept at 130°C
for 1 h.After a vacuum distillation the yield of the product
20
was 10.55 g (94%), bp 57–59°C (20 mm Hg), d 0,9011,
4
2
0
20
20
n
1
1.4571 {bp 52.5°C (15 mm Hg), d 0.9025, nD
.4573 [2]}. H NMR spectrum, δ, ppm: 1.24 s [6H,
D
4
1
C(CH ) ], 1.92 s (3H, N=CCH ), 2.40 s (2H, CH ), 4.01
3
2
3
2
br.s (NH). Found, %: C 64.30; H 10.69; N 25.01.
C H N . Calculated, %: C 64.24; H 10.78; N 24.97.
6
12
2
5
-Methyl-3,5-diethyl-2-pyrazoline (IIb). To 14.2 g
B
A
(0.1 mol) of methyl ethyl ketone azine (Ib) was added at
room temperature while stirring 0.05 g (0.2 mmol) of I2.
The reaction mixture self-heated to 50–60°C, then it was
heated for 1 h at 140°C. After a vacuum distillation the
IIa−IIb
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Kukharev
