Microwave-assisted synthesis of bithiazole derivatives under solvent-free conditions

Full text of DOI:10.1007/s11178-005-0216-9

Russian Journal of Organic Chemistry, Vol. 41, No. 4, 2005, pp. 623–624. From Zhurnal Organicheskoi Khimii, Vol. 41, No. 4, 2005, pp. 632–633.
Original English Text Copyright © 2005 by Hashemi, Asadollahi, Mostaghim.
SHORT
COMMUNICATIONS
Microwave-Assisted Synthesis of Bithiazole Derivatives
under Solvent-Free Conditions*
M. M. Hashemi, H. Asadollahi, and R. Mostaghim
Department of Chemistry, Sharif University of Technology, P.O. Box 11365-9516, Tehran, Iran;
e-mail: mhashemi@sharif.edu
Received January 22, 2004
Bithiazole derivatives play an important role in the
synthesis of polymers possessing magnetic properties
[1], manufacture of high-performance electrolumines-
cent devices such as light-emitting diodes [2], and
medicine. For example, aminoalkyl derivatives of
2,4'-bithiazole-4-carboxylic acid were shown to exhibit
antitumor activity [3]. Another field of application
of bithiazole derivatives includes synthesis of macro-
bicyclic cryptands [4].
morillonite as acid catalyst. 2,2'-Bithiazole derivatives
were synthesized as follows: 2 equiv of α-bromobenzyl
or bromomethyl phenyl ketone was mixed with 1 equiv
of dithiooxamide and 2 g of K10 montmorillonite. The
mixture was thoroughly ground in a mortar, transferred
into a beaker, and irradiated in a microwave furnace
over a period indicated in table (2.5–6 min). After ap-
propriate treatment, 2,2'-bithiazoles IIa and IIb were
isolated in 60 and 75% yield, respectively (see table).
4,4'-Bithiazoles IVa–IVc were obtained in a similar
way from the corresponding thioamides IIIa–IIIc and
1,4-dibromo-2,3-butanedione at a reactant ratio of 2:1.
For comparison, compound IIa was also synthesized
by conventional procedure: dithiooxamide was dis-
solved in anhydrous ethanol, the solution was trans-
ferred into a flask containing α-bromo ketone Ia, and
the mixture was heated for 18 h under reflux with
stirring using a magnetic stirrer. The progress of the
reaction was monitored by TLC. When the reaction
was complete, the mixture was cooled to room tem-
perature, and compound IIa was separated by filtration
and recrystallized from benzene. Yield 24% [10].
Bithiazoles are usually prepared by heating under
severe conditions of α-halo ketones or ketones having
another readily departing group in the α-position [5]
with thioamides or thioureas in the presence of
a strong mineral acid (e.g., hydrobromic acid) [6].
These reactions are time-consuming [2, 7, 8], and the
target products are obtained in low yields. In the pre-
ceding study we synthesized benzimidazole derivatives
by reaction of o-phenylenediamine with ortho esters
under microwave irradiation in the absence of solvent
[9]. The present communication describes the syn-
thesis of bithiazole derivatives under analogous condi-
tions. The procedure is based on the condensation of
thioamides or thiourea with α-halo ketones under
microwave irradiation in the presence of K10 mont-
Thus the proposed procedure ensures preparation of
bithiazole derivatives in good yields without a solvent.
O
S
Ph
R
Ph
R
N
S
N
S
K10, MW
R
NH2
2
+
Ph
H2N
Br
S
Ia, Ib
IIa, IIb
O
S
R
R
N
N
K10, MW
Br
+
2
Br
R
NH2
S
S
O
IIIa–IIIc
IVa–IVc
I, II, R = Ph (a), H (b); III, IV, R = Ph (a), Me (b), NH2 (c).
* The original article was submitted in English.
1070-4280/05/4104-0623 © 2005 Pleiades Publishing, Inc.

HASHEMI et al.
Synthesis of 2,2'- and 4,4'-bithiazole derivatives under microwave irradiation without a solvent
624
Initial comp. no. Product no.
Reaction time, min (power, %)a
Yield,b %
mp, °C (published data)
6 (70)
60
75
74
70
54
238–239 (238 [10, 11])
219–220 (222 [12])
Ia
IIa
0.5 (100)+2 (50)
3 (100)
Ib
IIb
186–187 (187 [13])
IIIa
IIIb
IIIc
IVa
IVb
IVc
2 (100)+2 (70)
2 (100)+3 (70)
169–170 (167 [14])
242 decomp. (240 decomp. [6, 7])
a
The reaction time and irradiation power were optimized from the results of several experiments; 100% corresponds to 1000 W.
Isolated product.
b
1
It takes a short time and is ecologically friendly.
Unlike known methods, the reaction occurs under mild
conditions and needs no catalysis by strong mineral
acids.
The H and 13C NMR spectra were recorded on
a Bruker DRX-500 Avance spectrometer. The IR spec-
tra were measured in KBr on an Unicam Matson 1000
Fourier spectrometer. The reaction mixtures were irra-
diated in a Butan M-245 domestic microwave furnace.
All the products have been reported previously.
They were identified by comparing their spectral
parameters and physical properties with those of
authentic samples. In all experiments, the progress of
reactions was monitored by TLC. Compounds IIa and
IIb exhibit fluorescent properties, and they are readily
detected under UV light (λ 366 nm). Initial α-bromo
ketones were prepared by addition of bromine in
a dropwise manner to the corresponding carbonyl
compounds, followed by heating under reflux until
disappearance of the bromine color.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 4 2005