Photoconversions of 1-acetyl-2,2,4-trimethyl[2H]dihydroquinoline [4]

Full text of DOI:10.1007/s10593-005-0253-x

Chemistry of Heterocyclic Compounds, Vol. 41, No. 7, 2005
PHOTOCONVERSIONS OF 1-ACETYL-
2,2,4-TRIMETHYL-[2H]-DIHYDROQUINOLINE
B. S. Lukyanov, M. B. Lukyanova, and N. V. Volbushko
Keywords: dihydroquinoline, photoreaction product, photochromism.
The photochromic properties of [2H]-dihydroquinolines, observed earlier at -196°C [1], have not yet
been studied in detail. We have observed that when a solution of 1-acetyl-2,2,4-trimethyl-[2H]-dihydroquinoline
(1) [2] in dioxane is exposed to light with λmax 313 nm at room temperature, its photocoloration occurs with
formation of a stable photoinduced form. To monitor the course of the process, we withdrew test samples from
the solution and recorded their absorption spectra (Specord M-40). Irradiation was stopped within 12 h, after the
optical density of the absorption band for the photoinduced form (λmax 420 nm) stopped increasing and the
absorption band at λmax 310 nm of the starting compound 1 disappeared. The photoreaction product was
1
successfully separated chromatographically into 2 fractions, which were identified by IR and H NMR
spectroscopy.
The 1H NMR spectrum was taken on a Varian Unity-300 (300 MHz), internal standard TMS.
The first fraction, a colored (λmax 420 nm) solid (mp 146-147°C), was identified as the open form
1-acetyl-2,2,4-trimethyl-[2H]-dihydroquinoline (N-acetylacetone anil) 3. In the IR spectrum (Specord IR-75),
there is an absorption band at 1670 cm-1 for the stretching vibrations of the C=O group of the N-acetyl moiety
(νCO 1682 cm-1 for the closed form 1). 1H NMR spectrum, δ, ppm: 1.20 (6H, s, C(CH3)2); 1.90 (3H, s, CH3); 2.25
(N–CO–CH3); 5.10 (1H, s, arom.); 6.45-7.05 (4H, m, C6H4).
Me
Me
Me
N
COMe
Me
N
3
Me
N
60%
40%
hν
Me
Me
Me
Me
Me
N
Me
COMe
COMe
Me
Me
Me
Me
2
1
N
H
H
4
5
__________________________________________________________________________________________
Scientific Research Institute of Physical and Organic Chemistry, Rostov State University, Rostov-on-
Don 344090, Russia; e-mail: bluk@ipoc.rsu.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii,
No. 7, pp. 1103-1105, July, 2005. Original article submitted March 13, 2005.
936
0009-3122/05/4107-0936©2005 Springer Science+Business Media, Inc.

The second fraction, a colorless oil, was identified as 2,2,4-trimethyl-[2H]-dihydroquinoline (acetone
anil) (5) and contains an absorption band at 3375 cm-1, which coincides with the band for the stretching vibration
1
1
of the NH group in the IR spectrum of acetone anil [3]. The H NMR spectrum also matches the H NMR
spectrum of acetone anil [3], δ, ppm: 1.10 (6H, s, C(CH3)2); 1.83 (3H, s, CH3); 3.60 (1H, s, NH); 5.05 (1H, s,
arom.); 6.05-6.9 (4H, m, C6H4).
Thus we may have the following scheme for conversions of 1-acetyl-2,2,4-trimethyl-[2H]-
dihydroquinoline (1) when it is exposed to light with λmax 313 nm in dioxane at room temperature:
This work was carried out with the financial support of the Russian Foundation for Fundamental
Research (grant 04-03-32485) and grant NSh-945.2003.3.
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3.
J. Kols and R. S. Becker, J. Am. Chem. Soc., 91, 6513 (1969).
W. A. Cliffe, J. Chem. Soc., 1327 (1933).
C. C. Tung, Tetrahedron, 19, 1685 (1963).
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