Free radicals: XXVII. Synthesis of 2,6-diphenyl-4-[p-(2,6-diphenyl-4-pyridyl)phenyl]pyranyl

Article abstract of DOI:10.1023/A:1020339120810

Starting with 2,6-diphenyl-4-(p-tolyl)pyridine a synthesis of 2,6-diphenyl-4-[p-(2,6-diphenyl-4-pyridyl)phenyl]pyrylium perchlorate was performed. By reduction of the latter the corresponding radical was obtained. The radical was shown to be unstable with respect to oxygen.

Full text of DOI:10.1023/A:1020339120810

Russian Journal of Organic Chemistry, Vol. 38, No. 6, 2002, pp. 830 832. Translated from Zhurnal Organicheskoi Khimii, Vol. 38, No. 6, 2002,
pp. 872 874.
Original Russian Text Copyright
2002 by Tanaseichuk, Pryanichnikova, Burtasov, Sysmanov.
Free Radicals: XXVII.* Synthesis
of 2,6-Diphenyl-4-[p-(2,6-diphenyl-4-pyridyl)phenyl]pyranyl
B. S. Tanaseichuk, M. K. Pryanichnikova, A. A. Burtasov, and V. V. Sysmanov
Ogarev Mordovian State University, Saransk, 430000 Russia
Received November 23, 2001
Abstract Starting with 2,6-diphenyl-4-(p-tolyl)pyridine a synthesis of 2,6-diphenyl-4-[p-(2,6-diphenyl-4-
pyridyl)phenyl]pyrylium perchlorate was performed. By reduction of the latter the corresponding radical
was obtained. The radical was shown to be unstable with respect to oxygen.
2,4,6-Triphenylpyranyl was shown formerly to
belong to the electron-excessive radicals [2] that
should be stabilized by electron-withdrawing sub-
stituents.
VII difficult to separate and having according to TLC
on Silufol plates Rf 0.82, 0.30, 0.70 respectively
(eluent chloroform).
Therefore we attempted to synthesize 2,6-diphenyl-
4-[p-(2,6-diphenyl-4-pyridyl)phenyl]pyranyl (I). We
expected that introduction of the pyridine moiety
would stabilize the radical both due to its electron-
withdrawing property and because of increased de-
localization of the unpaired electron.
The synthesis of the radical was carried out along
the scheme.
2,4-Diphenyl-4-(p-tolyl)pyrylium perchlorate (II)
was prepared by boiling p-methylbenzaldehyde with
acetophenone in the presence of perchloric acid.
Perchlorate II is a yellow crystalline substance, it is
well soluble in acetic acid, acetone, dioxane, limited-
ly soluble in alcohol, and insoluble in water and ether.
Thus in the reaction mixture alongside the initial
bromomethyl derivative IV were present products of
hydrolysis VI and of oxidation VII.
Therefore the replacement of halogen in compound
IV by hydroxy group was carried out via an inter-
mediate stage involving formation of 2,6-diphenyl-4-
(p-acetoxymethylphenyl)pyridine (V) by boiling
compound IV in glacial acetic acid with anhydrous
sodium acetate with subsequent alkaline hydrolysis of
compound V in alcohol-water mixture (1: 1). Reac-
tion products V and VI were isolated in crystalline
Perchlorate II was converted into 2,6-diphenyl-4-
(p-tolyl)pyridine (III) by boiling with concentrated
ammonia solution. Reaction product III is a white
crystalline substance well soluble in acetone, chloro-
form, dioxane, alcohol, ether.
The bromination of 2,6-diphenyl-4-(p-tolyl)pyri-
dine (III) with N-bromosuccinimide in dry carbon
tetrachloride with benzoyl peroxide as initiator
state. In the IR spectrum of compound V is present an
1
absorption band at 1730 cm
characteristic of
furnished
2,6-diphenyl-4-(p-bromomethylphenyl)-
carbonyl group, and in the IR spectrum of compound
pyridine (IV) in virtually qualitative yield.
IV is observed a broad absorption band of hydroxy
1
group in the 3250 3400 cm
region.
The hydrolysis of compound IV in dimethylform-
amide failed to substitute directly a hydroxy group
for the halogen in the methyl group of compound IV.
We obtained instead a mixture of compounds IV, VI,
Oxidation of 2,6-diphenyl-4-(p-hydroxymethyl-
phenyl)pyridine (VI) with cerium(IV) ammonium
nitrate at boiling in the glacial acetic acid afforded
2,5-diphenyl-4-(p-formylphenyl)pyridine (VII) as
evidenced
*
For communication XXVI, see [1].
1070-4280/01/3806-830$27.00 2002 MAIK Nauka/Interperiodica

FREE RADICALS: XXVII.
831
Scheme.
by the presence in the IR spectrum of a carbonyl
group band in the 1720 cm region.
relatively low reaction temperature that cannot be
sufficiently increased with benzene as solvent.
1
The solution of radical I in dioxane is crimson,
and the color rapidly disappears on contact with air.
Thus contrary to expectations radical I is instable
against oxygen. This fact hampered isolation of the
radical in crystalline form. ESR spectrum of the
radical is a singlet, and we failed to observe hyperfine
structure.
2,6-Diphenyl-4-[p-(2,6-diphenyl-4-pyridyl)phenyl]-
pyrylium perchlorate (VIII) was prepared by con-
densation with acetophenone in the same way as com-
pound II.
Although the reducing system Zn/benzene acetic
acid water (1: 1: 1) is usually applied to the synthesis
of pyranyl radicals [3], salt VIII does not practically
be reduced with this agent.
EXPERIMENTAL
The best method of radical I preparation is reduc-
tion of perchlorate VIII with metallic sodium in dry
dioxane under inert atmosphere in a Schlenk flask.
IR spectra were recorded on spectrophotometer
UR-20 from solutions in CCl4. ESR spectrum was
registered on EPA 2m instrument. The p-methyl-
benzaldehyde was prepared by procedure [4].
Perchlorate VIII was also sufficiently readily
reduced by 1% sodium amalgam in dioxane under
inert atmosphere.
2,4-Diphenyl-4-(p-tolyl)pyrylium perchlorate
(II). A mixture of 8 g (8.16 ml, 68 mmol) of
p-methylbenzaldehyde, 11.3 g (11.5 ml, 94 mmol) of
acetophenone, 5 ml of 72% perchloric acid, and
The use of benzene as solvent decelerated the
reduction of the salt into the radical. It may be due to
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 6 2002

832
TANASEICHUK et al.
10 ml of toluene was boiled for 1 h. Then the reaction
mixture was cooled to room temperature, and 100 ml
of ether was added. The separated precipitate was
filtered off, washed with ether on filter, and re-
crystallized from acetic acid. Yield 4.576 g (16%).
mp273 274 C (publ. 275 C [5]). Found, %: C 68.24;
H 4.47. C24H19ClO4. Calculated, %: C 68.13;
H 4.53.
(eluent benzene). Yield 0.503 g (88%). mp 121
122 C. IR spectrum, , cm : 700, 1480, 1585, 1635
(aromatic ring); 3250 3400 (OH). Found, %: C
85.51; H 5.12. C24H19NO. Calculated, %: C 85.43;
H 5.38.
1
2,5-Diphenyl-4-(p-formylphenyl)pyridine (VII).
A mixture of 0.373 g (1.12 mmol) of 2,6-diphenyl-4-
(p-hydroxymethylphenyl)pyridine (VI), 1.03
g
(2.2 mmol) of cerium(IV) ammonium nitrate, 22 ml
of acetic acid, and 3 ml of water were boiled for 1 h
(till the solution lost its orange color). Then the reac-
tion mixture was cooled and poured into 30 ml of
water. The separated precipitate was filtered off and
purified by column chromatography on silica gel
(eluent chloroform). Yield 0.288 g (78%). mp 99
2,6-Diphenyl-4-(p-tolyl)pyridine (III). A mixture
of 4.58 g (11 mmol) of 2,4-diphenyl-4-(p-tolyl)pyryl-
ium perchlorate (II) and 180 ml of 25% aqueous
ammonia was boiled for 1.5 h. Then the reaction mix-
ture was cooled to room temperature, the separated
precipitate was filtered off, washed on filter with
water, and recrystallized from 2-propanol. Yield
2.784 g (78%). mp 120 121 C. Found, %: C 89.64;
H 5.94. C24H19N. Calculated, %: C 89.68; H 5.96.
1
100 C. IR spectrum, , cm : 1700, 1450, 1500,
1600, 3070, 3090 (aromatic ring); 1720 (C=O).
Found, %: C 85.75; H 5.25. C24H17NO. Calculated,
%: C 85.95; H 5.11.
2,6-Diphenyl-4-(p-bromomethylphenyl)pyridine
(IV). A mixture of 3.21 g (10 mmol) of 2,6-diphenyl-
4-(p-tolyl)pyridine (III), 1.78 g (10 mmol) of
N-bromosuccinimide, 27 ml of dry carbon tetra-
chloride, and 0.005 g of benzoyl peroxide was boiled
for 1 h. Then the reaction mixture was cooled, the
separated precipitate was filtered off. The mother
liquor was evaporated in a vacuum. The crystals
obtained were subjected to column chromatography
on SiO2 (eluent carbon tetrachloride). Yield 3.8 g
2, 6-Diphenyl-4-[p-(2, 6-diphenyl-4-pyridyl)-
phenyl]pyrylium perchlorate (VIII). A mixture of
0.335 g (1 mmol) of 2,5-diphenyl-4-(p-formylphenyl)-
pyridine (VII), 0.73 g (0.75 ml, 6 mmol) of aceto-
phenone, 0.5 ml of 72% of perchloric acid, and
1.5 ml of toluene was boiled for 1 h. Then the reac-
tion mixture was cooled to room temperature, and
20 ml of ether was added. The separated yellow
precipitate was filtered off, washed with ether on
filter, and recrystallized from acetic acid. Yield
0.51 g (80%), mp 130 C.
1
(95%). mp 123 124 C. IR spectrum, , cm : 1450,
1585, 1635, 3050 (aromatic ring); 700 (C Br); 3480
(N H). Found, %: C 72.35; H 4.55. C24H18BrN.
Calculated, %: C 72.01; H 4.53.
Preparation of solution of 2,6-diphenyl-4-[p-
(2,6-diphenyl-4-pyridyl)phenyl]pyranyl (I) in di-
oxane. Compound I was prepared in a Schlenk flask
in a flow of carbon dioxide. First was charged 50 ml
of dry dioxane and 0.01 g of sodium metal, and the
system was flushed with carbon dioxide. Then in a
flow of carbon dioxide was added 0.13 g of 2,6-di-
phenyl-4-[p-(2,6-diphenyl-4-pyridyl)phenyl]pyrylium
perchlorate (VIII). The reaction was boiled fro 2 h to
formation of a crimson solution.
2,6-Diphenyl-4-(p-acetoxymethylphenyl)pyridine
(V). A mixture of 0.84 g (2.1 mmol) of 2,6-diphenyl-
4-(p-bromomethylphenyl)pyridine (IV), 1g (12mmol)
of anhydrous sodium acetate, and 12.6 ml (12.6 g,
210 mmol) of glacial acetic acid was boiled for 3 h.
Then the reaction mixture was cooled, poured into
35 ml of water, and neutralized by 10% solution of
sodium carbonate. The separated precipitate was
filtered off and purified by column chromatography
on silica gel (eluent ethyl acetate). Yield 0.653 g
REFERENCES
1
(82%). mp 74 75 C. IR spectrum, , cm : 1450,
1. Tanaseichuk, B.S., Pryanichnikova, M.K., and Tikho-
nova, L.G., Zh. Org. Khim., 1999, vol. 35, no. 3,
pp. 466 468.
2. Tanaseichuk, B.S., Tomilin, O.B., and Butin, K.P.,
Zh. Org. Khim., 1982, vol. 18, no. 2, pp. 241 246.
3. Palchkov, V.A., Zhdanov, Yu.A., and Dorofeen-
ko, G.N., Zh. Org. Khim., 1965, vol. 1, no. 6, p. 1171.
4. Sint. Org. Prep., Sb. 2, Moscow: Inostr. Lit., 1949;
n-Toluilovyi al,degid, pp. 364 466.
1585, 1635, 3050 (aromatic ring); 1730 (C=O); 1260
(C O C); 3460 (N H). Found, %: C 82.70; H 5.75.
C26H21NO2. Calculated, %: C 82.32; H 5.54.
2,6-Diphenyl-4-(p-hydroxymethylphenyl)pyri-
dine (VI). A mixture of 0.653 g (1.7 mmol) of
2,6-diphenyl-4-(p-acetoxymethylphenyl)pyridine (V),
0.653 g (5.18 mmol) of potassium hydroxide, 25 ml
of ethanol, and 25 ml of water was boiled for 2 h. On
cooling the separated precipitate was filtered off and
purified by column chromatography on silica gel
5. Simalty-Siemiatycki, M. and Fugnitto, R., Bull. Soc.
Chim., 1965, no. 7, pp. 1944 1950.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 6 2002