S-benzylation of 5-benzylidene-2-thioxodihydropyrimidine-4,6(1H,5H)-dione under conditions of phase-transfer catalysis

Full text of DOI:10.1134/S1070363209080337

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 8, pp. 1760–1761. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.I. Rakhimov, S.A. Avdeev, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 8, pp. 1402–1403.
LETTERS
TO THE EDITOR
S-Benzylation of 5-Benzylidene-2-thioxodihydropyrimidine-
4,6(1H,5H)-dione Under Conditions of Phase-Transfer Catalysis
A. I. Rakhimova and S. A. Avdeevb
a Volgograd State Technical University,
pr. Lenina, 28, Volgograd, 400131 Russia
e-mail: organic@vstu.ru
bInstitute of Chemical Problems of Ecology, Russian Academy of Natural Sciences, Volgograd, 400066 Russia
e-mail: rakhimov@sprint-v.com.ru
Received February 9, 2009
DOI: 10.1134/S1070363209080337
It has been shown earlier [1] that S-benzylation of
thiobarbituric acid in the water-dioxane medium gives
rise to 2-(benzylthio)pyrimidine-4,6(1H,5H )dione and
is determined by stability of generated thiolate anion A.
chloride with 5-benzylidene-2-thioxodihydropyrimidine-
4,6-(1H,5H )-dione I:
O
H
N
In this report we consider the influence of benzylidene
group incorporation into position 5 of 2-thioxodihyd-
ropyrimidine-4,6(1H,5H)dione on the electronic struc-
ture of the generated thiolate anion B and the use of
the latter for the synthesis of (5Z)-5-benzylidene-2-
(benzylthio)pyrimidine-4,6(1H,5H )-dione.
S
N
H
O
I
O
N
The quantum-chemical analysis by АМ1 method
[2, 3] of anion B generated from the 5-benzylidene
derivative indicates that its stability increases (EB =
H
N
KOH
_K+
_
–2693.8 kcal mol–1 as compared with EA
=
S
O
–2693.8 kcal mol–1) accompanied with decrease of
electronic density on the sulfur atom (SA = –0.450 in
comparison with SB = –0.458). This leads to anion B
reactivity decrease in comparison with anion A:
B
O
H
S
O
O
N
C6H5CH2Cl
_Cl_
H
H
N
N
N
O
S
N
O
B
S
N
A
O
_
_
0.450
0.458
II
EА –1345.5 kcal mol–1
EВ –2693.8 kcal mol–1
It was established that use of dibenzo-18-crown-6
as a phase-transfer catalyst permitted to increase the
yield of (5Z)-5-benzylidene-2-(benzylthio)pyrimidine-4,6-
(1H,5H)-dione II from 16 to 35%. Reaction was
carried out with toluene as organic phase and
potassium hydroxide water solution as water phase.
This fact underlies the low reactivity of 5-benzyl-
idene substituted thiolate anion in the nucleophilic
substitution reactions, in particular, at the chlorine
substitution in benzyl chloride. In this connection we
used phase-transfer catalysis in the reaction of benzyl
1760

S-BENZYLATION OF 5-BENZYLIDENE-2-THIOXODIHYDROPYRIMIDINE-4,6(1H,5H)-DIONE
1761
1
The published data analysis [4] shows that dibenzo-
18-crown-6 gives rise to the most stable complex with
potassium cation. This fact confirms the need to use
just potassium hydroxide as a base.
The H NMR spectrum was registered on a Varian
Mercury device (300 MHz) in DMSO-d6 relative to
internal HMDS. Melting points were determined in
accordance with procedure [5].
(5Z)-5-Benzylidene-2-(benzylthio)pyrimidine-4,6-
(1H,5H)-dione (II). To a suspension of 1.5 g (6.5 mmol)
of I in 15 ml of water was dropwise added a solution
of 0.4 g (6.5 mmol) of potassium hydroxide in 25 ml
of water. This mixture was stirred for 45 min. To the
suspension obtained were added 120 ml of toluene,
0.8 ml (7.2 mmol) of benzyl chloride and 0.1 g of
dibenzo-18-crown-6. The mixture was stirred for 7 h.
Then a solid phase was filtered off, washed with water
and recrystalled from anhydrous ethanol. Yield 0.7 g
REFERENCES
1. Rakhimov, A.I., Avdeev, S.А. and Le Thi Doan Chang,
Zh. Obshch. Khim., 2009, vol. 79, no. 2, p. 348.
2. Schmidt, M.W., Baldridge, K.K., and Boatz, J.A.,
J. Comput. Chem., 1993, vol. 14, p. 1347.
3. Voets, R., J. Comput. Chem., 1990, vol. 11, p. 269.
4. Khiraoka, M., Kraun-soyedineniya. Svojstva i prime-
neniye (Crown Compounds. Properties and Applica-
tion), Moscow: Mir, 1986, p. 363.
1
(35%), mp 182–1830С (decomp.). Н NMR spectrum,
δ, ppm: 4.26 m (2Н, СН2–С6H5), 5.96 s (1Н, C=СН–),
6.92–7.45 m (10Н, НAr), 11.7 s (1Н, NH). Found, %:
N 9.58. C18H14N2O2S. Calculated, %: N 8.69.
5. Stepin, B.D., Tekhnika laboratornogo eksperimenta v
khimii (Laboratory Experimental Technique in The
Chemistry), Moscow: Khimiya, 1999, p. 600.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 8 2009