On the mechanism of intramolecular cyclization of dialkyl(2-propynyl)[3- alkenyl(or aryl)-2-propynyl]-ammonium salts

Article abstract of DOI:10.1007/s11178-005-0170-6

Given are experimental data indicating that base-catalyzed intramolecular cyclization of ammonium salts containing a 2-propynyl-like group together with a 3-alkenyl- or 3-aryl-2-propynyl group follows a concerted mechanism involving the 3-alkenyl- or 3-aryl-2-propynyl moiety as π⁴-fragment.

Full text of DOI:10.1007/s11178-005-0170-6

Russian Journal of Organic Chemistry, Vol. 41, No. 3, 2005, pp. 358–360. Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 3, 2005,
pp. 369–371.
Original Russian Text Copyright © 2005 by E. Chukhadzhyan, Gevorkyan, El. Chukhadzhyan, Kinoyan.
On the Mechanism of Intramolecular Cyclization
of Dialkyl(2-propynyl)[3-alkenyl(or aryl)-2-propynyl]-
ammonium Salts
E. O. Chukhadzhyan, A. R. Gevorkyan, El. O. Chukhadzhyan, and F. S. Kinoyan
Institute of Organic Chemistry, National Academy of Sciences of Armenia, ul. Z. Kanakertsi 167a, Erevan, 375091 Armenia
e-mail: hasulik4@mail.ru
Received August 28, 2002
Abstract—Given are experimental data indicating that base-catalyzed intramolecular cyclization of ammonium
salts containing a 2-propynyl-like group together with a 3-alkenyl- or 3-aryl-2-propynyl group follows a con-
certed mechanism involving the 3-alkenyl- or 3-aryl-2-propynyl moiety as π4-fragment.
We previously showed that ammonium salts con-
taining β,γ-unsaturated groups and various 4-en-2-ynyl
fragments on the nitrogen atom readily undergo base-
catalyzed intramolecular cyclization (like Diels–Alder
reaction) to afford 2,2-dialkylisoindolium or 2,2-di-
alkyldihydroisoindolium salts and their fused analogs
in almost quantitative yield [1–7] (Scheme 1).
of species A or B which undergoes fast aromatization
via hydride (pathway a) or proton transfer (pathway b;
Scheme 2). The other scheme includes isomerization
of the 3-alkenyl- or 3-aryl-2-propynyl group to allenyl
fragment, cyclization of the salt thus formed, and
aromatization of the latter to dihydroisoindole deriva-
tive (Scheme 3). Scheme 3 is consistent with published
data on cyclization of acetylenic compounds [16–20].
For example, base-catalyzed intramolecular cycliza-
tion of compounds with the general formula
X(CH2C≡CC6H5)2 (X = CH2, S, NCH3, O), as well as
of allyl and 2-propynyl ethers derived from 3-isopro-
penyl-2-propynyl and 3-phenyl-2-propynyl alcohols,
was presumed to be preceded by isomerization into the
corresponding α-allenyl derivative [16–18].
Scheme 1.
N
OH–
N
or
N
With the goal of establishing the true mechanism of
the cyclization, Babayan and co-workers previously
performed kinetic studies using UV spectroscopy
[8–15]. However, this method did not allow the
authors to detect formation of intermediate species, in
Two schemes were proposed for cyclization of the
above systems [1, 3, 8–15]. According to the first of
these, the cyclization involves intermediate formation
Scheme 2.
H
N
a
OH–
A
N
N
H
N
b
H
OH
B
1070-4280/05/4103-0358 © 2005 Pleiades Publishing, Inc.

ON THE MECHANISM OF INTRAMOLECULAR CYCLIZATION
359
particular salts containing an allene moiety. On the
basis of the effects of structural and external factors on
the rate of cyclization, the authors presumed that the
second scheme is more probable.
I–V), whose intensity gradually decreased. In no case
absorption assignable to allene group was detected.
It might be presumed that we failed to detect
α-allene fragment because of very fast cyclization with
participation of that group. To verify this assumption
we examined the behavior of trimethyl(3-phenyl-2-
propynyl)ammonium bromide (VIII), which cannot
undergo cyclization, in the presence of a catalytic
amount of aqueous alkali. We observed no absorption
typical of an allene fragment, while the band belonging
to disubstituted acetylene moiety did not change its
position and intensity. Figure illustrates variation of the
IR spectral pattern during cyclization of salt V. It is
seen that the spectra recorded at different moments
lack absorption band assignable to allene moiety.
Scheme 3.
H
OH–
R
R
R
R
H
N
N
·
R
R
R
R
H
N
N
H
In the present work we made an attempt to
Thus the results of our IR studies led us to conclude
that the cyclization of ammonium salts having a 2-pro-
pynyl group together with a 3-alkenyl- or 3-aryl-2-
propynyl moiety follows a concerted mechanism
which directly involves the enyne group as π4-frag-
ment, i.e., according to Scheme 2.
elucidate the mechanism of cyclization of quaternary
ammonium salts containing a β,γ-unsaturated group
together with a 3-alkenyl- or 3-aryl-2-propynyl radical
on the nitrogen atom. The study was performed using
IR spectroscopy, and we found optimal conditions for
the cyclization to occur in water-resistant cells (CaF2).
As substrates we used dimethyl(2-propynyl)(3-vinyl-2-
propynyl)ammonium, dimethyl(3-phenyl-2-propynyl)-
(2-propynyl)ammonium, diethyl(3-phenyl-2-propynyl)-
(2-propynyl)ammonium, dicyclohexyl(3-phenyl-2-pro-
pynyl)(2-propynyl)ammonium, 4-(3-phenyl-2-propyn-
yl)-4-(2-propynyl)morpholinium, dimethylbis(3-phe-
nyl-2-propynyl)ammonium, and diethylbis(3-phenyl-2-
propynyl)ammonium salts I–VII.
EXPERIMENTAL
The IR spectra of salts I–III, VI, and VII were
recorded on a UR-20 spectrometer, and the spectra of
IV and V were obtained on a Specord IR75 instrument.
X
Me
Me
R
R
N
N
1
Ph
I
II–VII
II, R = Me, X = H; III, R = Et, X = H; IV, R = cyclo-C6H11,
X = H; V, R2N = morpholino, X = H; VI, R = Me, X = Ph;
VII, R = Et, X = Ph.
In all cases, the IR spectra of aqueous solutions
of salts I–VII were initially recorded, a 2 N solution
of potassium hydroxide was added, the mixture was
quickly stirred and placed into a spectrophotometric
cell, and the progress of reaction was monitored fol-
lowing variations in the IR spectra.
Had the cyclization followed Scheme 2, the IR
spectra recorded during the process would display
absorption in the region 1940–1960 cm–1, typical of
allene fragment. However, in the cyclization of salts
I–VII, the IR spectra contained only absorption bands
due to disubstituted (2220–2240 cm–1) and monosub-
stituted triple bonds (2110–2130 cm–1; compounds
2400
2200
2000
1800 ν, cm–1
IR monitoring of the cyclization of 4-(3-phenyl-2-propynyl)-
4-(2-propynyl)morpholinium salt V: (1) initial spectrum.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 3 2005

CHUKHADZHYAN et al.
360
7. Chukhadzhyan, E.O., Gevorkyan, A.R., Chukhad-
zhyan, El.O., Shakhatuni, K.G., Kinoyan, F.S., and
Panosyan, G.A., Khim. Geterotsikl. Soedin., 2004, p. 34.
8. Babayan, A.T. and Abramyan, I.A., Dokl. Akad. Nauk
Arm. SSR, 1970, vol. 50, p. 144.
9. Abramyan-Babayan, I.A. and Babayan, A.T., Arm.
Khim. Zh., 1972, vol. 25, p. 19.
10. Abramyan-Babayan, I.A., Atomyan, A.V., and Baba-
yan, A.T., Arm. Khim. Zh., 1972, vol. 25, p. 30.
Salts I–VII were synthesized according to the proce-
dures described in [1–3]; salt VIII was prepared by
alkylation of dimethyl(3-phenyl-2-propynyl)amine
with methyl bromide in anhydrous diethyl ether. Potas-
sium hydroxide of chemically pure grade was used.
A 2 N aqueous solution of potassium hydroxide,
0.04–0.08 ml, was added to a 15–20% solution of
salt I–VIII, 0.2 ml. The mixture was transferred into
a spectrophotometric cell, and the progress of the
reaction was monitored following variation of the IR
spectral pattern. While preparing solutions of poorly
soluble salts II, VI, and VII, a few drops of ethanol
were added.
11. Babayan, A.T., Atomyan, A.V., Kislina, I.S., and Vin-
nik, M.I., Arm. Khim. Zh., 1975, vol. 28, p. 958.
12. Abramyan-Babayan, I.A., Atomyan, A.V., and Baba-
yan, A.T., Dokl. Akad. Nauk Arm. SSR, 1973, vol. 57,
p. 81.
13. Atomyan, A.V., Churkina, N.P., Babayan, A.T., Kisli-
na, I.S., and Vinnik, M.I., Arm. Khim. Zh., 1981, vol. 34,
p. 389.
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