Reduction of 2-perfluoroalkanoylcyclohexan-1,3-diones under the conditions of ionic hydrogenation

Full text of DOI:10.1134/S1070363208050290

ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 5, pp. 1007–1008. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © T.S. Khlebnikova, V.G. Isakova, F.A. Lakhvich, 2008, published in Zhurnal Obshchei Khimii, 2008, Vol. 78, No. 5, pp. 864–865.
LETTERS
TO THE EDITOR
Reduction of 2-Perfluoroalkanoylcyclohexan-1,3-diones
Under the Conditions of Ionic Hydrogenation
T. S. Khlebnikova, V. G. Isakova, and F. A. Lakhvich
Institute of Bioorganic Chemistry, Belarus National Academy of Sciences,
ul. Akad. Kuprevicha 5/2, Minsk, 220141 Belarus
e-mail: khlebnicova@boch.bas-net.by
Received December 20, 2007
DOI: 10.1134/S1070363208050290
2-Perfluoroalkanoylcyclohexan-1,3-diones we de-
scribed recently [1,2] present significant interest as the
promising building blocks for introducing poly-
fluoroalkyl groups in various carbo- and hetero-cyclic
systems. Unlike nonfluorinated cyclic β,β'-triketones
[3] the chemistry of these compounds is studied
unsufficiently, and investigation of their chemical
transformations, in particular, in reduction, is an im-
portant problem for the chemistry and the synthetic use
of these polyfunctional compounds. The ionic
hydrogenation of nonfluorinated 2-cycloalkan-1,3-
diones is known to proceed regioselectively with the
prevailing hydrogenolysis of the keto group in the side
chain to give the methylene group and resulting in the
formation of 2-alkylcycloalkan-1,3-diones [4]; this has
been successfully used for the synthesis of
prostaglandines [5] and phytoprostanes [6].
The aim of this work is the investigation of the
behavior of 2-perfluorocyclohexan-1,3-diones Ia, Ib
under the conditions of ionic hydrogenation. It was
found that the ionic hydrogenation of 2-trifluoroacetyl-
Ia and 2-pentafluoropropyonyl dimedone IIa with
triethylsilane in trifluoroacetic acid in the presence of
lithium perchlorate within 5 h at room temperature
resulted in the reduction of exocyclic carbonyl group
to hydroxy one to afford diketoalcohols IIa, IIb in
81% and 89% yield respectively. At the increased
reaction time (24 h and more) only compounds IIa, IIb
were isolated.
OH OH
RF
O
O
O
OH
RF
RF
Et3SiH/LiClO4
CF3COOH
O
O
O
Ia, Ib
IIa, IIb
RF = CF3 (a), C2F5 (b).
Hence, unlike the nonfluorinated cyclic β,β'-
triketones the reduction of 2-perfluoroacylcyclohexan-
1,3-diones Ia, Ib under the conditions of ionic
hydrogenation leads to selective formation of
diketoalcohols IIa, IIb that can be ascribed to the
effect of the electron-accepting perfluoroalkyl
substituent.
diones and their derivatives. The results will be
described in further publications.
The structure of diketoalcohols synthesized IIa, IIb
existing in the enol form was confirmed by IR and 1H,
13C, and 19F NMR spectroscopy and the elemental
analysis.
The starting compounds Ia, Ib were prepared
according to procedure [1, 2].
We used the ionic hydrogenation for the reduction
of the other polyfluorinated 2-acylcyclohexan-1,3-
1007

1008
KHLEBNIKOVA et al.
ppm: −81.53 s (3F, CF3), −121.29 d.d (1F, JFF 270, JFH
6 Hz), −128.30 d.d (1F, JFF 269, JFH 22 Hz). Found, %:
C 45.92, H 4.61. C11H13F5O3. Calculated, %: C 45.84,
H 4.55.
2-(1-Hydroxy-2,2,2-trifluoroethyl)-5,5-dimethyl-
cyclohexan-1,3-dione (IIa). To a solution of 1 mmol
of compound Ia in 2 ml of trifluoroacetic acid 2 ml of
1% lithium perchlorate solution in trifluoroacetic acid
and 4 mmol of triethylsilane were added. The reaction
mixture was stirred at room temperature for 5 h.
Trifluoroacetic acid was distilled in a vacuum, the
residue was washed with small amount of n-hexane (4 ×
4 ml) and crystallized from the acetone−hexane
mixture. Yield 81%, mp 83−86°C. The IR spectrum, ν,
NMR spectra were taken on a Bruker Avance-500
spectrometer, internal reference TMS for 1H (500 MHz)
13
19
and C (125 MHz), and CCl3F, for F (470 MHz. IR
spectra were recorded on an UR-20 spectrometer from
KBr pellets. Melting points were measured in a
Boetius block. The reaction progress and the purity of
the compounds obtained were monitored by TLC on
Silufol UV-254 plates, eluent ether.
1
cm−1: 1615 (C=O conjugated), 155 (C=C). H NMR
spectrum (CDCl3), δ, ppm: 1.08 (6H, 2CH3), 2.31 d
(2H, CH2, J 17.1 Hz), 2.36 d (2H, CH2, J 17.1 Hz),
13
5.40 m (1H, CHOH). C NMR spectrum (Py-d5), δC,
REFERENCES
ppm: 27.98, 31.93, 47.93, 67.38 q (3JCF 32 Hz),
105.87, 126.07 q (1JCF 285 Hz), 190.42. 19F NMR
spectrum (CDCl3), δF, ppm: −76.68 d (JFH 7 Hz).
Found, %: C 50.51, H 5.56. C10H13F3O3. Calculated,
%: C 50.42, H 5.50.
1. Khlebnicovaб T.S., Zinovichб V.G., and Lakhvich, F.A.,
Dokl. Nat. Acad. Nauk Belarus, 2005, vol. 49, no. 5,
p. 72.
2. Khlebnicova, T.S., Isakova, V.G., Baranovsky, A.V.,
Borisov, E.V., and Lakhvich, F.A., J. Fluorine Chem.,
2006, vol. 127, no. 12, p. 1564.
2-(1-Hydroxy-2,2,3,3,3-pentafluoropropyl)-5,5-
dimethylcyclohexan-1,3-dione (IIb) was obtained
analogously from the compound Ib. Yield 89%, mp
90−93°C. IR spectrum, ν, cm−1: 1610 (C=O con-
3. Rubinov, D.V., Rubinova, I.L., and Akhrem, A.A.,
Chem. Rev., 1999, vol. 99, no. 4, p. 1047.
4. Akhrem, A.A., Lakhvich, F.A., Lis, L.G., Khripach, V.A.,
Fil’chenkov, N.A., Kozinets, V.A., and Pashkov-
skii, F.S., Dokl. Akad. Nauk SSSR, 1990, vol, 311, no. 6,
p. 1381.
5. Lakhvich, F.A. and Kozinets, V.A., Zh. Org. Khim.,
1997, vol. 33, no. 1, p.53.
1
1
jugated), 1555 (C=C). H NMR spectrum H (CDCl3),
δ, ppm: 1.09 s (6H, 2CH3), 2.32 d (2H, CH2, J 17.1 Hz),
2.36 d (2H, CH2, J 17.1 Hz), 5.53 d.d (1H, CH−OH, J
18.0, 7.6 Hz). 13C NMR spectrum (Py-d5), δC, ppm:
28.04, 31.94, 47.78, 66.81 d.d (2JCF 28, 23 Hz), 105.59,
2
115.62 t.q (1JCF 258, JCF 34 Hz), 120.46 q.t (1JCF 287,
6. Schmidt, A. and Boland, W., J. Org. Chem., 2007, vol. 72,
no. 6, p. 1699.
2JCF 36 Hz), 190.05. 19F NMR spectrum (Py-d5), δF,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 5 2008