Oxidation of 3,3,3-trifluoro-1-(4-methoxyphenyl)propyne in the system PbO2-CF3COOH-CH2Cl2

Full text of DOI:10.1134/S1070428013040222

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 4, pp. 621–623. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © H.M.H. Alkhafaji, A.V. Vasilyev, D.S. Ryabukhin, A.P. Rudenko, V.M. Muzalevskiy, V.G. Nenajdenko, 2013, published in Zhurnal
Organicheskoi Khimii, 2013, Vol. 49, No. 4, pp. 636–638.
SHORT
COMMUNICATIONS
Dedicated to the 100th Anniversary of Corresponding Member
of the Russian Academy of Sciences A.A. Petrov
Oxidation of 3,3,3-Trifluoro-1-(4-methoxyphenyl)propyne
in the System PbO2–CF3COOH–CH2Cl2
H.M.H. Alkhafajia, A. V. Vasilyeva, b, D. S. Ryabukhina, A. P. Rudenkoa,
V. M. Muzalevskiyc, and V. G. Nenajdenkoc
a St. Petersburg State Forest Technical University, Institutskii per. 5, St. Petersburg, 194021 Russia
e-mail: aleksvasil@mail.ru
b St. Petersburg State University, Universitetskii pr. 26, St. Petersburg, 198504 Russia
c Moscow State University, Vorob’evy gory 3, Moscow, 119899 Russia
e-mail: nen@acylium.chem.msu.ru
Received January 17, 2013
DOI: 10.1134/S1070428013040222
We previously showed [1] that one-electron oxida-
tion of acetylenic compounds ArC≡CX in the system
PbO2–CF3CO2H–CH2Cl2 leads to the formation of dif-
ferent products, depending on the nature of electron-
withdrawing X substituent. If X = CO2R, COAr, COR,
PO(OEt)2 (medium-strength acceptors), tetrasubstitut-
ed ethenes X(ArCO)C=C(COAr)X are formed, where-
as stronger acceptor groups (X = COCF3, COCO2R,
CN) give rise to furan derivatives.
The present communication reports on the oxida-
tion and electrophilic reactions of 3,3,3-trifluoro-1-(4-
methoxyphenyl)propyne (I) in the system PbO2–
CF3CO2H–CH2Cl2. Trifluoromethyl-substituted acety-
lenes constitute an interesting class of highly reactive
compounds that are promising due to their specific
properties arising from the presence of an electron-
withdrawing CF3 group [2].
methylene chloride, the major product was ketone III
(Kucherov reaction). Electrophilic addition of tri-
fluoroacetic acid molecule to the triple C≡C bond of I
gives vinyl trifluoroacetate which undergoes hydrol-
ysis upon treatment of the reaction mixture with water
to afford compound III [3, 4]. In this reaction we
detected only a small amount of diketone II resulting
from oxidative dimerization of alkyne I.
The reverse order of addition of the reactant, i.e.,
addition of I to preliminarily prepared oxidation sys-
tem, ensures sharp increase of the yield of II (to 38%),
though ketone III is also formed as a result of con-
current electrophilic reaction (Scheme 1).
1
The H, 19F, and 13C NMR spectra of II contained
only one set of signals, indicating stereoselective
formation of a single diastereoisomer among two pos-
sible for structure II (meso form or racemate). We plan
to elucidate the steric structure of II by X-ray analysis.
When the oxidant (PbO2) was added to a solution of
compound I in a mixture of trifluoroacetic acid and
Scheme 1.
O
CF3
O
PbO2–CF3COOH–CH2Cl2
20°C, 1 h
Ar
CF3
+
Ar
Ar
CF3
II, 38%
O
Ar
CF3
III, 20%
I
CF3COOH, 20°C, 1 h
III, 96%
Ar = 4-MeOC6H4.
621

ALKHAFAJI et al.
622
Scheme 2.
PbO2–CF3COOH
CH2Cl2
·
I
Ar
CF3
–e–
A
F3C
CF3
Ar
A
2CF3COOH
–2H+
F3C
CF3
Ar
2H2O
B
II
O
O
·
–2 CF3COOH
F3C
CF3
Ar
Ar Ar
·
CF3COOH
–H+
O
O
C
F3C
O
CF3
IV
O
C
Ar = 4-MeOC6H4.
Two alternative mechanisms may be proposed for
the formation of diketone II. The first one implies
dimerization of initially generated radical cation A to
give dication B which takes up two trifluoroacetic acid
molecules with formation of buta-1,3-diene-1,4-diyl
bis(trifluoroacetate) (IV). An alternative path of the
transformation of radical cation A is the reaction with
CF3CO2H with formation of vinyl radical C and its
dimerization to bis(trifluoroacetate) IV (Scheme 2).
Hydrolysis of the latter yields bis-enol which
tautomerizes to diketone II. It should be noted that the
presence of two electron-withdrawing CF3 groups in
IV prevent it from undergoing further oxidation.
1,4-Diketones like II are difficultly accessible com-
pounds. The only known representative of this class of
compounds was obtained previously as an inseparable
mixture with two other products by radical addition of
propionaldehyde to bis(trifluoromethyl)acetylene [5].
Such 1,4-diketones are very promising from the view-
point of their use in the synthesis of various trifluoro-
methyl-substituted five- and six-membered hetero-
cyclic compounds.
Oxidation of 3,3,3-trifluoro-1-(4-methoxyphe-
nyl)propyne (I). Compound I, 200 mg (1 mmol), was
added at 20°C under vigorous stirring to a suspension
of 239 mg (1 mmol) of PbO2 in a mixture of 0.38 ml
(5 mmol) of CF3CO2H and 3 ml of CH2Cl2. The mix-
ture was stirred for 1 h at 20°C and poured into 100 ml
of chloroform. The resulting solution was washed with
water (2×20 ml), a saturated aqueous solution of
NaHCO3 (2×20 ml), and water again (20 ml) and dried
over Na2SO4, the solvent was distilled off, and the
residue was subjected to chromatographic separation
on a column charged with silica gel using petroleum
ether (bp 40–70°C)–diethyl ether as eluent. We isolat-
ed 82 mg (38%) of II and 44 mg (20%) of III.
3,3,3-Trifluoro-1-(4-methoxyphenyl)propan-1-one
(III) was described in [3, 4].
1,4-Bis(4-methoxyphenyl)-2,3-bis(trifluorometh-
yl)butane-1,4-dione (II). mp 190–192°C. IR spectrum
(KBr): ν 1670 cm–1 (C=O). 1H NMR spectrum, δ, ppm:
3.91 s (6H, MeO), 5.13 br.m (2H, CH), 7.01 d (4H,
H
arom, J = 8.7 Hz), 8.04 d (4H, Harom, J = 8.7 Hz).
13C NMR spectrum, δC, ppm: 46.5 q (CH, JCF
25.8 Hz), 55.7 (OMe), 114.4 q, 123.6 q (CF3, JCF
=
=
280.6 Hz), 128.9, 131.5, 164.9, 189.1 (C=O). 19F NMR
spectrum: δF –59.18 ppm, d (CF3, JHF = 6.1 Hz). Mass
spectrum, m/z (Irel, %): 434 (60) [M]+, 432 (42), 299
(7), 281 (12), 279 (10), 135 (100), 107 (43), 92 (62).
Found, %: C 55.39; H 3.68. C20H16F6O4. Calculated,
%: C 55.31; H 3.71. M 434.09.
1
The H, 13C, and 19F NMR spectra were measured
at 20°C on a Bruker AM-500 spectrometer at 500,
125.76, and 470 MHz, respectively, using CDCl3 as
solvent and reference (for H and 13C; CHCl3,
1
δ 7.26 ppm; CDCl3, δC 77.0 ppm); the 19F chemical
shifts were determined relative to CFCl3 (δF 0.0 ppm).
The IR spectra were recorded on an FSM-1201 spec-
trometer. The mass spectra were obtained on a Agilent
Technologies 6850s G2570A GC/MSD instrument
(HP-5MS capillary column, 3 m×0.25 mm, film thick-
ness 0.25 μm; oven temperature programming from
50 to 290°C at a rate of 5 deg/min; injector tempera-
ture 290°C; electron impact, 70 eV). Elemental anal-
ysis was performed on a EuroVector EA-300 analyzer.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 4 2013

OXIDATION OF 3,3,3-TRIFLUORO-1-(4-METHOXYPHENYL)PROPYNE
623
p. 2249; Rulev, A.Yu., Muzalevskiy, V.M., Kondra-
shov, E.V., Ushakov, I.A., Shastin, A.V., Balenkova, E.S.,
Haufe, G., and Nenajdenko, V.G., Eur. J. Org. Chem.,
2010, p. 300; Goldberg, A.A., Muzalevskiy, V.M.,
Shastin, A.V., Balenkova, E.S., and Nenajdenko, V.G.,
J. Fluorine Chem., 2010, vol. 131, p. 384; Nenajden-
ko, V.G., Muzalevskiy, V.M., Shastin, A.V., Balenko-
va, E.S., and Haufe, G., J. Fluorine Chem., 2007,
vol. 128, p. 818; Nenajdenko, V.G., Varseev, G.N., Korot-
chenko, V.N., Shastin, A.V., and Balenkova, E.S.,
J. Fluorine Chem., 2004, vol. 125, p. 1339; Korotchen-
ko, V.N., Shastin, A.V., Nenajdenko, V.G., and Balenko-
va, E.S., Tetrahedron, 2001, vol. 57, p. 7519.
nos. 12-03-31040-mol-a, 13-03-01129-a) and by the
Ministry of Education and Science of the Russian
Federation (Federal Grant-in-Aid Program “Human
Capital for Science and Education in Innovative
Russia” for 2009–2013; Agreement no. 14.B37.21.0794
from September 3, 2012).
REFERENCES
1. Vasil’ev, A.V., Aristov, S.A., Fukin, G.K., Kozha-
nov, K.A., Bubnov, M.P., and Cherkasov, A.V., Russ. J.
Org. Chem., 2008, vol. 44, p. 791.
3. Alkhafaji, H.M.H., Ryabukhin, D.S., Muzalevskiy, V.M.,
Osetrova, L.V., Vasilyev, A.V., and Nenajdenko, V.G.,
Russ. J. Org. Chem., 2013, vol. 49, p. 327.
4. Alkhafadji, H.M.H., Ryabukhin, D.S., Muzalev-
skiy, V.M., Vasilyev, A.V., Fukin, G.K., Shastin, A.V., and
Nenajdenko, V.G., Eur. J. Org. Chem., 2013, p. 1132.
2. Rulev, A.Yu., Ushakov, I.A., Kondrashov, E.V., Muzalev-
skiy, V.M., Nenajdenko, V.G., and Shastin, A.V.,
J. Fluorine Chem., 2011, vol. 132, p. 945; Nenajden-
ko, V.G., Muzalevskiy, V.M., Balenkova, E.S., Shas-
tin, A.V., Kondrashov, E.V., Ushakov, I.A., and
Rulev, A.Yu., J. Org. Chem., 2010, vol. 75, p. 5679;
Muzalevskiy, V.M., Nenajdenko, V.G., Balenkova, E.S.,
Shastin, A.V., and Haufe, G., Synthesis, 2009, no. 13,
5. Chambers, R.D., Jones, C.G.P., and Silvester, M.J.,
J. Fluorine Chem., 1986, vol. 32, p. 309.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 4 2013