Benzazoles. 1. Acylation of benzothiazolin-2-ones by aromatic acid chlorides using small amounts of zinc chloride

Article abstract of DOI:10.1023/A:1015647606680

We show that the yield of 6-aroylbenzothiazolin-2-ones, products of acylation of benzothiazolin-2-ones by aromatic acid chlorides in the presence of ZnCl₂, depends on the degree of nucleophilicity of benzothiazolin-2-ones.

Full text of DOI:10.1023/A:1015647606680

Chemistry of Heterocyclic Compounds, Vol. 38, No. 3, 2002
BENZAZOLES. 1. ACYLATION OF
BENZOTHIAZOLIN-2-ONES BY
AROMATIC ACID CHLORIDES USING
SMALL AMOUNTS OF ZINC CHLORIDE
N. S. Mukhamedov, D. A. Dushamov, N. A. Aliev, Kh. M. Bobokulov, M. G. Levkovich,
and N. D. Abdullaev
We show that the yield of 6-aroylbenzothiazolin-2-ones, products of acylation of benzothiazolin-2-ones
by aromatic acid chlorides in the presence of ZnCl
benzothiazolin-2-ones.
2
, depends on the degree of nucleophilicity of
Keywords: 6-aroylbenzothiazolin-2-ones, aromatic acid chlorides, acylation.
Reactions of acylation of the aromatic ring in benzazolin-2-ones have been little studied.
Benzimidazolin-2-ones can be condensed with anhydrides [1-4] and chlorides [5-8] of carboxylic acids in the
presence of excess anhydrous AlCl to form the corresponding C-acylbenzimidazolin-2-ones. The corresponding
3
6
-acylbenzoxazolin-2-ones are synthesized by reaction of benzoxazolin-2-ones with aliphatic acid chlorides in
the presence of excess anhydrous AlCl
3
[9,10], while in the case of aromatic acid chlorides, 6-
aroylbenzoxazolin-2-ones are obtained by using small amounts of ZnCl
been previously studied for benzothiazolin-2-ones.
2
[11]. The indicated reactions have not
In this work, we have studied acylation of benzothiazolin-2-ones by aromatic acid chlorides using small
amounts of ZnCl
presented in Table 1.
2
. The physicochemical characteristics of 6-aroylbenzothiazolin-2-ones 3a-g obtained are
COCl
N
R
O
ZnCl2
O
C
N
R
+
S
S
O
R'
R'
1
a,b
2
a–d
3a–g
1
a R = H, b R = Me; 2 a R'= H, b R'= 2-Br, c R'= 4-Br, d R'= 3-Me;
3
a R = R'= H, b R = H, R'= 2-Br, c R = H; R'= 4-Br, d R = H, R'= 3-Me,
e R = Me, R'= 2-Br, f R = Me, R'= 4-Br, g R = Me, R'= 3-Me
_
_________________________________________________________________________________________
Institute of Plant Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent 700170.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 380-384, March, 2002. Original article
submitted December 28, 1999.
3
44
0009-3122/02/3803-0344$27.00©2002 Plenum Publishing Corporation

TABLE 1. Physicochemical Characteristics of the Synthesized Compounds 3a-g
Found, %
IR spectrum, ν, cm-1
Com-
Empirical
formula
——————
mp, °С
Mass spectrum, m/z (Irel, %)
Calculated, %
Yield, %
pound
(ethanol)
C
H
N
М+
A+
B+
С=О
NH
3200
3220
3250
3300
—
3
3
3
3
3
3
3
а
b
c
d
e
f
С14Н9NO2S
65.48
3.14
3.52
5.82
5.49
209-211
197-199
266-268
234-236*
131-133
162-164
139-141*
255
42)
333/335
38)
333/335
36)
269
44)
347/349
35)
347/349
40)
283
32)
178
77
1650, 1710
1655, 1705
1655, 1700
1660, 1710
1650, 1710
1650, 1710
1660, 1705
57
53
67
45
81
84
72
6
5.88
(
(100)
(23)
С14Н8BrNO2S
С14Н8BrNO2S
С15Н11NO2S
С15Н10BrNO2S
С15Н10BrNO2S
С16Н13NO2S
50.81
2.81
3.93
178
155/157
5
0.37
2.39
4.19
(
(100)
(27)
49.93
2.01
2.39
4.67
4.19
178
155/157
(31)
5
0.37
(
(100)
67.24
3.86
4.95
178
91
6
6.91
4.08
5.20
(
(100)
(25)
52.03
2.65
2.87
3.90
4.02
192
155/157
5
1.79
(
(100)
(23)
51.88
2.69
4.19
192
155/157
(26)
—
5
1.79
2.87
4.02
(
(100)
g
67.99
4.41
4.59
5.05
4.94
192
91
—
6
7.84
(
(100)
(28)
_
*
____
Solvent: benzene.

To determine the optimal acylation conditions and to determine the limits for use of small amounts of
catalyst, we studied the effect of the amount of ZnCl , temperature, and the reaction time on the yield of
benzoylation product of benzothiazolin-2-one 1a. The best yield of 6-benzoylbenzothiazolin-2-one (3a) was
2
-2
obtained for reagent ratio 1a:2a:ZnCl of 1:1.2:1·10 and when the reaction mass was heated for 3 h at 200°C to
2
2
10°C. Increasing the amount of catalyst did not increase the yield of the product 3a, while decreasing the
amount of catalyst down to 0.1 mmol only resulted in traces of product.
As shown by our study, the yields of the acylation products of 3-methylbenzothiazolin-2-one (1b) are
higher than for benzothiazolin-2-one 1a. This probably can be explained by the higher nucleophilicity of
compound 1b, similar to what was observed in acylation of benzoxazolin-2-ones [11].
1
The structure of the synthesized compounds 3a-g was demonstrated by IR and H NMR spectroscopy
and mass spectrometry, and confirmed by elemental analysis and an alternate synthesis.
In methylation of 6-aroylbenzothiazolin-2-ones 3b-d by dimethyl sulfate in alkaline medium, we
obtained 6-aroyl-3-methylbenzothiazolin-2-ones 3e-g in quantitative yields that were identical to the products of
direct acylation of compound 1b.
Me
H
N
N
O
C
O
C
NaOH
R'
+
Me SO
2 4
S
O
S
O
R'
3
b–d
3e–g
For the IR spectra of compounds 3a-g (Table 1), typically absorption bands appear for the stretching
-1
vibrations of the carbonyl group in the 6 position (1650-1660 cm ) and out-of-plane bending vibrations of the
-
1
-1
CH bonds of the 1,2,4-trisubstituted benzene ring (805-825 cm and 870-885 cm ).
The mass spectra of compounds 3a-g, independent of the nature of the substituents R and R', show the
+
same type of fragmentation with rupture of the Ar–CO bond and formation of the fragments A (M -Ar) and B
(
Ar) (Table 1). Fragmentation directions related to elimination of the benzothiazolin-2-one ring are weakly
expressed.
1
The H NMR spectra of compounds 3a-g (Table 2) also support their structure. In the part of the
spectrum characteristic of the benzothiazolin-2-one ring, we observe H-4 doublet at 7.04-7.21 ppm with ortho
coupling constant J = 8.39 Hz, H-5 doublet of doublets at 7.66-7.77 ppm with ortho and meta coupling
constants J = 8.40 Hz and J = 1.68 Hz, and also H-7 doublet at 7.81-7.93 ppm with meta coupling constant
J = 1.68 Hz. In the aromatic part of the spectrum, there are five one-proton multiplets at 7.29-7.79 ppm.
Downfield, we observe a broad signal at 9.15-11.6 ppm which is characteristic of the NHCO– group. In the
spectra of compounds 3e-g, the methylation products of 6-aroyl derivatives 3b-d, a singlet appears from protons
of the methyl group at 3.44-3.46 ppm.
EXPERIMENTAL
The IR spectra of the studied compounds were recorded on an UR-20 spectrometer in KBr disks. The
1
+
H NMR spectra were taken on an UNITY 400 plus spectrometer (Varian) in CDCl
3
. The mass spectra were
obtained on a MS 25-RF (Kratos) with direct injection of the sample into the ion source (ionizing electron
energy 70 eV, ion source temperature 250°C, temperature of the sample injection system 200°C). The course of
the reactions and the purity of the synthesized compounds were monitored by TLC (Silufol UV-254,
benzene–ethanol, 21:4, visualizing agent: 1 g of KMnO
4
+ 4 ml of conc. H
2
SO
4
+ 96 ml of H O).
2
Benzothiazolin-2-one 1a was obtained by the procedure [12], and its 3-methyl derivative 1b was
obtained by the method [13].
3
46

1
TABLE 2. H NMR Spectral Characteristics of Compounds 3a-g
Com-
1H NMR spectrum (CDCl3), δ, ppm, (spin–spin coupling constant, J, Hz)
pound
Н-4
Н-5
Н-7
α
β
γ
α'
β'
3-H/3-Me
Ar–Me
—
3
a
7.21 (1Н, d,
J45 = 8.42)
7.77 (1Н, dd,
J45 = 8.42,
J57 = 1.58)
7.93 (1Н, d,
J75 = 1.58)
7.79 (1Н, dd,
Jαβ = 8.40;
7.51 (1Н, br. t,
Jβα = 8.40,
7.61 (1Н, tt,
7.79
7.51 (1Н, br. t, 9.15
Jβ’α = 8.40,
= 7.69)
Jγβ = Jγβ’ = 7.69, (1Н, dd,
(1Н,
J
αγ
= 1.71)
J
βγ
= 7.69)
J
γα
= J = 1.71) Jα’β = 8.40,
γα’
J
β’γ
br. s)
Jα’γ = 1.71)
3
b
7.14 (1Н, d,
J45 = 8.39)
7.68 (1Н, dd,
J54 = 8.39,
J57 = 1.68)
7.83 (1Н, d,
J75 = 1.68)
7.60 (1Н, dd,
Jαβ = 7.93,
7.32 (1Н, td,
Jβα = 7.93,
7.38 (1Н, td,
—
7.29 (1H, dd,
9.91
(1Н,
br. s)
—
—
Jγβ = Jγβ’ = 7.48,
Jβ’γ = 7.48,
J
αγ
= 1.22)
J = 7.48,
βγ
J
γα
= 1.22)
—
J
ββ’
= 1.91)
Jββ’ = 1.91)
3
3
c
7.10 (1Н, d,
J45 = 8.39)
7.66 (1Н, dd,
J54 = 8.39,
J57 = 1.68)
7.81 (1Н, d,
J75 = 1.68)
7.58 (1Н, s)
7.58 (1Н, s)
7.58 (1Н, s)
7.58 (1Н, s)
10.44
(1Н,
br. s)
d
7.13 (1Н, dd, 7.69 (1Н, dd,
J45 = 8.39,
J47 = 0.46)
7.82 (1Н, dd, 7.46 (1Н, dtd,
7.31 (1H, t,
7.35 (1Н, dtd,
Jγβ = 7.79,
7.51 (1H, br. s,
11.16
2.37
(3Н, s)
J54 = 8.39,
J57 = 1.68)
J75 = 1.67,
J74 = 0.46)
Jαβ =7.32,
= J = 1.68,
Jβγ = 7.79,
Jα’γ = Jα’α = 1.68,
(1Н,
J
αγ
α’α
J
βα
= 7.32)
J
γα
= J = 1.68,
γα’
J
α’β
= 0.91,
br. s)
JαMe = 0.61)
JγМе = 0.61)
Jα’Me = 0.61)
3
e
7.04 (1Н, d,
J45 = 8.40)
7.75 (1Н, dd,
J54 = 8.40,
J57 = 1.68)
7,82 (1Н, dd, 7.60 (1Н, dd,
7.32 (1Н, td,
Jβα = 7.79,
7.38 (1Н, td,
—
7.29 (1H, dd,
3.44
—
J75 = 1.68,
J74 = 0.39)
Jαβ = 7.79,
= 1.22)
Jγβ = Jγβ’ = 7.48,
Jβ’γ = 7.48,
(3Н, s)
J
αγ
J
βγ
= 7.48,
J
γα
= 1.22)
—
J
β’β
= 1.91)
Jββ’ = 1.91)
7.57 (1Н, s)
3
3
f
7.06 (1Н, d,
J45 = 8.39)
7.73 (1Н, dd,
J54 = 8.39,
J57 = 1.84)
7.84 (1Н, d,
J75 = 1.84)
7.57 (1Н, s)
7.57 (1Н, s)
7.57 (1Н, s)
3.46
—
(3Н, s)
g
7.06 (1Н, dd, 7.77 (1Н, dd,
J45 = 8.39,
J47 = 0.46)
7,88 (1Н, dd, 7.46 (1Н, dtd,
7.31 (1H, t,
7.35 (1Н, dtd,
Jγβ = 7.63,
7.52 (1H, br. s,
—
3.45
2.37 (3Н, s,
J54 = 8.39,
J57 = 1.67)
J75 = 1.67,
J74 = 0.46)
Jαβ =7.32,
= J = 1.68,
Jβγ = 7.63,
Jα’γ = Jα’α = 1.68,
(3Н, s)
JMeα = JМеγ
J
αγ
α’α
J
βα
= 7.32)
J
γα
= J = 1.68,
γα’
J
α’β
= 0.91,
= J
Меα’
=
JαMe = 0.61)
JγМе= 0.61)
Jα’Me = 0.61)
= 0.61)

6
-Benzoylbenzothiazolin-2-one (3a). Mixture of compound 1a (1.51 g, 10 mmol), benzoyl chloride 2a
(
1.68 g, 12 mmol), and ZnCl (13.6 mg, 0.1 mmol) in nitrobenzene (15 ml) was heated for 3 h at 200°C to
2
2
10°C. The solvent was distilled off with steam and the residue was filtered out, washed with water, and dried.
Yield of compound 3a 1.45 g (57%).
Compounds 3b-g were obtained similarly.
6
-(2'-Bromobenzoyl)-3-methylbenzothiazolin-2-one (3e). Solution of dimethyl sulfate (1.51 g,
1
1
2 mmol) in 5% solution of NaOH (10 ml) was added with stirring to solution of compound 3b (3.33 g,
0 mmol) in 5% solution of NaOH (10 ml). The mixture was stirred for 2 h at room temperature and then the
precipitate was filtered out, washed with water, and dried. Obtained 3.3 g (95%) of compound 3e.
Compounds 3f,g were obtained similarly.
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48