ZnCl2-mediated synthesis of carboxylic anhydrides using 2-acyl-4,5-dichloropyridazin-3(2H)-ones

Article abstract of DOI:10.1081/SCC-200048939

ZnCl₂ is an efficient catalyst for synthesis of carboxylic acid anhydride from 2-acyl-4,5-dichloropyridazin-3(2H)-ones. Treatment of 2-acyl-4,5-dichloropyridazin-3(2H)-ones with ZnCl₂ (0.5 equivalents) and air in refluxing dry THF or

Full text of DOI:10.1081/SCC-200048939

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ZnCl ‐Mediated Synthesis of
2
Carboxylic Anhydrides using
2
‐Acyl‐4,5‐dichloropyridazin‐3(2H)
a
a
a
Yong‐Dae Park , Jeum‐Jong Kim , Ho‐Kyun Kim
b
a
c
,
Su‐Dong Cho , Young‐Jin Kang , Ki Hun Park
,
a
a
Sang‐Gyeong Lee & Yong‐Jin Yoon
a
Department of Chemistry and Research Institute
of Basic Sciences , Gyeongsang National University ,
Chinju, 660‐701, Korea
b
Research Institute of Natural Sciences , Changwon
National University , Changwon, Korea
c
Department of Agricural Chemistry, Division of
Applied Life Science (BK21 program) , Gyeongsang
National University , Chinju, Korea
Published online: 28 Jul 2007.
To cite this article: Yong‐Dae Park , Jeum‐Jong Kim , Ho‐Kyun Kim ,
Su‐Dong Cho , Young‐Jin Kang , Ki Hun Park , Sang‐Gyeong Lee & Yong‐Jin
Yoon (2005) ZnCl ‐Mediated Synthesis of Carboxylic Anhydrides using
2
2
‐Acyl‐4,5‐dichloropyridazin‐3(2H)‐ones, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 35:3, 371-378, DOI:
0.1081/SCC-200048939
1
To link to this article: http://dx.doi.org/10.1081/SCC-200048939

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Synthetic Communications , 35: 371–378, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200048939
ZnCl -Mediated Synthesis of Carboxylic
2
Anhydrides using 2-Acyl-4,5-
dichloropyridazin-3(2H)-ones
Yong-Dae Park, Jeum-Jong Kim, and Ho-Kyun Kim
Department of Chemistry and Research Institute of Basic Sciences,
Gyeongsang National University, Chinju, Korea
Su-Dong Cho
Research Institute of Natural Sciences, Changwon National University,
Changwon, Korea
Young-Jin Kang
Department of Chemistry and Research Institute of Basic Sciences, Gyeongsang
National University, Chinju, Korea
Ki Hun Park
Department of Agricural Chemistry, Division of Applied Life Science
(
BK21 program), Gyeongsang National University, Chinju, Korea
Sang-Gyeong Lee and Yong-Jin Yoon
Department of Chemistry and Research Institute of Basic Sciences, Gyeongsang
National University, Chinju, Korea
Abstract: ZnCl
2
is an efficient catalyst for synthesis of carboxylic acid anhydride from
-acyl-4,5-dichloropyridazin-3(2H)-ones. Treatment of 2-acyl-4,5-dichloropyridazin-
(2H) -ones with ZnCl (0.5 equivalents) and air in refluxing dry THF or acetonitrile
2
3
2
gave the corresponding symmetric acid anhydrides in good to excellent yield.
Keywords: Carboxylic acid anhydride, 2-acyl-4,5-dichloropyridazin-3(2H)-one, ZnCl2
Received in the USA October 24, 2004
Address correspondence to Yong-Jin Yoon, Department of Chemistry and Research
Institute of Basic Sciences, Gyeongsang National University, Chinju 660-701, Korea.
Fax: 082-055-761-0244. E-mail: yjyoon@nongae.gsnu.ac.kr

372
Y.-D. Park et al.
Recently, we reported on the acylation ability of 2-acyl-4,5-dichloropyrida-
zin-3(2H)-ones (1) for amines and the synthesis of 1,3,4-oxadiazoles
[
1,2]
using 2-acylpyridazin-3(2H)-ones.
applications of 2-acylpyridazin-3(2H)-ones, we found that the treatment of
-acyl-4,5-dichloropyridazin-3(2H)-ones (1) with zinc chloride and air in an
During the study of other synthetic
2
organic solvent at reflux gave the corresponding carboxylic anhydrides 2.
The ZnCl -mediated synthesis of carboxylic anhydrides using N-acyl-hetero-
2
cycle in air has not been reported to date.
Carboxylic anhydrides are useful acylating agents or intermediates in
organic synthesis because of the enhanced electrophilic character of the
[
3–10]
carbonyl group.
important for many transacylation applications
The availability of symmetric acid anhydrides is quite
because it precludes the
[11]
formation of by-products from the attack at the other acyl group present in
mixed anhydrides. Although many reagents for the synthesis of carboxylic
[
3,10–30]
acid anhydrides have been developed,
active even now. In the present study, we investigated the synthesis of car-
research in this field is still
boxylic anhydrides using 2-acyl-4,5-dichloropyridazin-3(2H)-ones (1) and
report a novel method using a ZnCl -mediated reaction sequence.
2
RESULTS AND DISCUSSION
First, we carried out the treatment of 1a with 0.5, 1 or 2 equivalents of zinc
chloride and air in dry tetrahydrofuran at room temperature (for Entries 1–3
in Table 1) or at reflux temperature (for Entry 4 in Table 1) under an air atmos-
phere. Zinc chloride (0.5 equivalents)/refluxing dry tetrahydrofuran (Entry 4)
was a good condition. To evaluate the solvent effect, the reaction was carried
out in various organic solvents such as tetrahydrofuran, methylene chloride,
acetonitrile, toluene, benzene, and methanol. From the preliminary exper-
iments (Entries 4–9), we chose tetrahydrofuran and acetonitrile as the
suitable solvent in our system. Acetonitrile was more efficient than tetrahydro-
furan (Entry 4 vs. Entry 5). It may be due to the difference in the dielectric
constant and/or the boiling point. We also performed the reaction of 1c in
the presence of various Lewis acids in refluxing acetonitrile (Scheme 1).
The results are summarized in Table 1 (Entries 10–16).
Among the nine Lewis acids, zinc halides and samarium iodide gave 2c in
excellent yield. Therefore we selected zinc chloride as the catalyst. 2-Aroyl-
4
,5-dichloropyridazin-3(2H)-ones 1b–g were treated with zinc chloride
0.5 equivalents) in air in refluxing dry tetrahydrofuran and acetonitrile to
(
give the corresponding symmetric anhydrides 2b–g in 73–97% yield, respect-
ively (Table 2). Although the reaction of 1h or 1i in refluxing tetrahydrofuran
did not give the corresponding anhydrides, treatment in refluxing acetonitrile
afforded 2h (91%) and 2i (90%), respectively (Entries 16 and 18 in Table 2).

ZnCl
2
-Mediated Synthesis of Carboxylic Anhydrides
373
Table 1. Reactions of carboxylic anhydrides with 1a-c in the presence of some
Lewis acids
Lewis acid
(equiv)
Reaction
condition
Time
(h)
a
b
Entry
1
2 (%)
1
2
3
4
5
6
7
8
9
1a -C H -Me(p)
ZnCl (2)
2
THF, rt
THF, rt
THF, rt
THF, rf
144
120
176
34
6
2a (46)
2a (90)
2a (89)
2a (89)
2a (93)
2a (85)
2a (50)
2a (40)
6
6
6
4
4
4
1a -C
1a -C
H
H
-Me(p)
-Me(p)
ZnCl
ZnCl
2
2
(1)
(0.5)
1a -C H -Me(p)
ZnCl (0.5)
2
6
6
6
4
4
4
1a -C
1a -C
H
H
-Me(p)
-Me(p)
ZnCl
ZnCl
2
2
(0.5)
(0.5)
CH
CH
3
2
CN, rf
Cl ,rf
2
35
36
36
1
c
c
1a -C H -Me(p)
ZnCl (0.5)
2
C H CH ,rf
6
6
6
6
4
4
4
5
3
1a -C
1a -C
H
H
-Me(p)
-Me(p)
ZnCl
ZnCl
2
2
(0.5)
(0.5)
C
MeOH,rf
6
H
6
,rf
d
—
10
11
12
13
14
15
16
1c -C H -OMe(p)
6
Zn (0.5)
ZnF (0.5)
CH CN, rf
3
17
115
10
10
8
2c (53)
2c (42)
2c (96)
2c (96)
2c (95)
4
1c -C H -OMe(p)
CH CN, rf
3
6
6
6
4
4
4
2
1c -C
1c -C
H
H
-OMe(p)
-OMe(p)
ZnBr
ZnI
SmI (0.5)
2
(0.5)
CH
CH
3
3
CN, rf
CN, rf
2
(0.5)
1c -C H -OMe(p)
CH CN, rf
3
6
6
6
4
4
4
2
1c -C
1c -C
H
H
-OMe(p)
-OMe(p)
CuCl
SnCl
2
(0.5)
(0.5)
CH
CH
3
3
CN, rf
CN, rf
24
24
2c (trace)
2c (trace)
2
a
b
c
rt ¼ Room temperature; rf ¼ Reflux.
Isolated yields.
Unknown product was formed. And the reaction did not finished for 36 h.
d
Methyl p-methylbenzoate was obtained in 83% yield.
The other product in this reaction, 4,5-dichloropyridazin-3(2H)-one could be
recovered quantitatively.
To provide evidence for the need of an oxygen source, we studied the
reaction of 1c in the presence of zinc chloride under three conditions.
Scheme 1.

374
Y.-D. Park et al.
Table 2. ZnCl -Mediated synthesis of carboxylic anhydrides using 2-aroylpyridazin-
2
(
2H)-ones 1
ZnCl
(equiv)
2
Time
(h)
a
b
Entry
1
Solvent
2 (%)
1
2
3
4
5
6
7
8
9
a -C H -Me(p)
6
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
THF
CH CN
34
6
2a (89)
2a (93)
2b (96)
2b (97)
2c (97)
2c (98)
2d (92)
2d (95)
2e (91)
2e (93)
2f (73)
2f (87)
2g (95)
2g (97)
2h (—)
2h (91)
2i (—)
2i (90)
4
a -C
b -C
6
H
4
-Me(p)
3
6
H
5
5
THF
CH CN
45
7
b -C H
6
3
c -C
c -C
6
H
H
4
-OMe(p)
-OMe(p)
THF
49
7
6
4
CH
THF
CH CN
3
CN
d -C H -Cl(p)
6
23
7
4
d -C
e -C
e -C H -C H (p)
6
H
4
-Cl(p)
3
6
H
4
-C
6
H
5
(p)
THF
CH CN
14
8
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
6
4
6
5
3
f -C H -Cl -2,4
6
THF
146
8
3
2
f -C
g -C
6
H
3
-Cl
c
2
-2,4
3
CH CN
4
H
3
O
THF
CH CN
11
7
c
g -C H O
4
3
3
h –(CH
h –(CH
i –CH3
2
)
)
4
CH
CH
3
3
THF
—
6
2
4
CH
THF
CH CN
3
CN
—
7
i –CH
3
3
a
b
Reaction temperature ¼ Reflux.
c
Isolated yield. 2-Furyl.
Firstly, 1c was refluxed in the presence of zinc chloride in dry acetonitrile to
give only anhydride 2c in excellent yield under an air atmosphere. However,
treatment of 1c in the presence of zinc chloride in refluxing dry acetonitile
under an argon atmosphere did not yield 2c. A mixture of 1c, zinc chloride,
a small amount of water (one drop), and acetonitrile was also refluxed to
afford 2c in excellent yield under an air atmosphere. In the presence of
excess water, however, 1c was transformed under the same condition to p-
methoxybenzoic acid as the main product and anhydride 2c. The reaction of
1
c and zinc chloride in the presence of a small amount of water under an
argon atmosphere did not provide 2c. Although the reaction was accelerated
by water, 1c competitively decomposed to p-methoxybenzoic acid in the
presence of excess water. These findings indicate that the oxygen in our
system is necessary for the formation of anhydrides 2.
In summary, we demonstrated a novel access and a simple method
synthesizing carboxylic anhydrides 2 from 2-acyl-4,5-dichloropyridazin-
3(2H)-ones and zinc chloride in air under neutral reaction conditions. The
method offers some advantages including easy preparation of 1 from

ZnCl
2
-Mediated Synthesis of Carboxylic Anhydrides
375
commercially available 4,5-dichloropyridazin-3(2H)-one, stability of 1 in air,
high yields of products, simple and convenient procedures, and a quantitative
recovery of reusable 4,5-dichloropyridazin-3(2H)-one. We are currently
investigating the detailed mechanism of this reaction.
EXPERIMENTAL
Reagents and solvents were used as received from the commercial sources.
TLC was performed on plates coated with silica gel (silica gel 60 F254,
Merck). The spots were located by UV light. Column chromatography was
carried out on silica gel (silica gel 60, 70–230 mesh). Melting points were
determined with a Thomas-Hoover capillary apparatus and are uncorrected.
1
13
H and C NMR spectra were obtained on a Br u¨ ker FT NMR-DRX 500 or
Varian Inova 300 Spectrometer. The chemical shift values were reported in
d units (part per million) relative to TMS as an internal standard. IR spectra
were obtained on a Hitachi 270-50 or Mattson Genesis Series FT-IR spectro-
photometer. Elemental analyses were performed with a Perkin Elmer 240 C.
General Procedure
2
a-g: A mixture of compound 1 (1.67 mmol), zinc chloride (0.83 mmol), and
dry tetrahydrofuran (30 mL) or dry acetonitrile (30 mL) was refluxed in air
until 1 disappeared by TLC monitoring. After cooling the mixture to room
temperature, the solvent was removed under reduced pressure. Diethyl
ether (30 mL) was added, the mixture was filtered and concentrated. The
residue was purified by column chromatography on silica gel (2.5 Â 3 cm)
using methylene chloride as eluent. Fractions containing anhydride 2 were
combined and evaporated under reduced pressure to give pure anhydride
2. Fractions containing pyridazinone were also combined and evapora-
ted under reduced pressure to afford 4,5-dichloropyridazin-3(2H)-one
quantitatively.
2
h-i: A mixture of compound 1 (11.5 mmol), zinc chloride (5.7 mmol),
and dry acetonitrile (60 mL) was refluxed in air until 1 disappeared. After
cooling the mixture to room temperature, the solvent was removed under
reduced pressure. Dry diethyl ether (30 mL) was added to the stirred
mixture. The mixture was filtered and concentrated. The residue was
purified by vacuum distillation to give the corresponding anhydride 2. The
filter residue was also dried in air to afford 4,5-dichloropyridazin-3(2H)-one.
4
-Methylbenzoic anhydride (2a). Light yellow solid, mp 88–908C
[22]
Lit.
1
[
mp 89–908C]; H NMR (CDCl ) d: 2.45 (s, 6H), 7.27 (d, 4H,
3
1
3
J ¼ 8 Hz), 8.03 (d, 4H, J ¼ 8 Hz); C NMR (CDCl ) d: 21.8, 126.3, 129.6,
3
1
30.6, 145.6, 162.6; IR (KBr): 3010, 2990, 1780, 1720, 1620, 1300, 1220,

376
Y.-D. Park et al.
2
180, 1040, 1000 cm . Anal. Calcd for C H O : C, 75.57; H, 5.55. Found
1
1
C, 75.68; H, 5.61.
1
6 14 3
[
22]
Benzoic anhydride (2b). Yellow solid, mp 40–418C [Lit.
mp
1
4
8
0–41 8C]; H NMR (CDCl ) d: 7.50–7.54 (m, 4H), 7.66–7.69 (m, 2H),
3
1
.16–8.25 (m, 4H); C NMR (CDCl ) d: 128.9, 129.0, 130.6, 134.5, 162.4;
3
3
2
1
IR (KBr): 3065, 1785, 1725, 1598, 1451, 1213, 1039, 720 cm . Anal.
Calcd for C H O : C, 74.33; H, 4.46. Found C, 74.41; H, 4.50.
1
4 10 3
4
-Methoxybenzoic anhydride (2c). Light yellow solid, mp 89–908C
[22]
1
[Lit.
mp 89–908C]; H NMR (CDCl ) d: 3.89 (s, 6H), 6.98 (m, 4H),
3
1
.09 (m, 4H); C NMR (CDCl ) d: 55.6, 114.2, 121.3, 132.8, 162.3, 164.6;
3
8
IR (KBr): 3010, 2990, 1790, 1720, 1620, 1300, 1220, 1180, 1040,
3
2
1
1000 cm . Anal. Calcd for C H O : C, 67.13; H, 4.93. Found C, 67.20;
16 14 5
H, 5.01.
4
H NMR (CDCl ) d: 7.50–7.52 (m, 4H), 8.06–8.08 (m, 4H); C NMR
-Chlorobenzoic anhydride (2d). Yellow solid, mp 184–1858C;
1
13
3
(
CDCl ) d: 127.1, 129.4, 131.9, 141.4, 161.3; IR (KBr): 3010, 1800, 1720,
3
2
600, 1500, 1400, 1220, 1180, 1060, 1000 cm ; Anal. Calcd for
1
1
C H O Cl : C, 56.98; H, 2.73; Cl, 24.03. Found C, 57.02; H, 2.81; Cl, 24.12.
1
4
8
3
2
4
-Phenylbenzoic anhydride (2e). Light yellow solid, mp 137–1398C
[22]
1
[
Lit.
mp 138–1408C]; H NMR (CDCl ) d: 7.43 (d, 2H, J ¼ 7.5 Hz),
3
7
8
1
1
6
.49 (t, 4H, J ¼ 7.5 Hz), 7.65 (d, 4H, J ¼ 7.5 Hz), 7.75 (d, 4H, J ¼ 8 Hz),
1
3
.24 (d, 4H, J ¼ 8.5 Hz); C NMR (CDCl ) d: 127.4, 127.6, 127.7, 128.6,
3
29.1, 131.2, 139.6, 147.4, 162.4; IR (KBr): 3010, 1770, 1730, 1600, 1500,
2
400, 1300, 1220, 1170, 1050, 980 cm ; Anal. Calcd for C H O : C,
1
1
6 14 5
7.13; H, 4.93. Found C, 67.20; H, 5.01.
,4-Dichlorobenzoic anhydride (2f). Light yellow solid, mp 120–
2
1
1
218C; H NMR (CDCl ) d: 7.38 (dd, 2H, J ¼ 10.0 Hz), 7.56 (d, 2H,
3
1
3
J ¼ 5.0 Hz), 7.97 (d, 2H, J ¼ 10.0 Hz); C NMR (CDCl ) d: 126.2, 127.5,
3
1
1
31.5, 133.6, 136.3, 140.5, 159.4; IR (KBr): 3010, 1800, 1740, 1600, 1560,
2
480, 1380, 1300, 1200, 1140, 1070, 1020 cm ; Anal. Calcd for
1
C H Cl O : C, 46.19; H,1.66; Cl, 38.96. Found C, 46.23; H, 1.71; Cl, 39.00.
1
4
6
4 3
Furan-2-carboxylic anhydride (2g). Light yellow solid, mp 68–698C;
1
H NMR (CDCl ) d: 6.61–6.62 (m, 2H), 7.42 (d, 2H, J ¼ 2.5 Hz), 7.71
3
1
3
(
d, 2H, J ¼ 1.0 Hz); C NMR (CDCl ) d: 112.9, 121.9, 143.2, 148.8,
3
1
53.1; IR (KBr): 3150, 1800, 1740, 1680, 1580, 1480, 1400, 1320, 1280,
2
1
1
Found C, 58.36; H, 2.98.
180, 1100, 1060, 1020 cm ; Anal. Calcd for C H O : C, 58.26; H, 2.93.
10 6 5
1
Hexanoic anhydride (2h). Colorless oil; H NMR (CDCl ) d: 0.88–0.92
m, 6H), 1.33–1.35 (m, 8H), 1.62–1.67 (m, 4H), 2.35 (t, 4H, J ¼ 7.8); C
NMR (CDCl ) d: 13.9, 22.3, 24.4, 31.2, 33.9, 179.9; IR (KBr): 2900, 2850,
3
1
3
(
3
2
1
1
H,10.35. Found C, 67.26; H, 10.35.
820, 1750, 1480, 1420, 1050 cm ; Anal. Calcd for C H O : C, 67.26;
12 22 3
1
Acetic anhydride (2i). Colorless oil; H NMR (CDCl ) d: 2.20 (s, 6H);
3
1
3
C NMR (CDCl ) d: 16.8, 166.0; IR (KBr): 2900, 2850, 1780, 1690, 1480,
3

ZnCl
2
-Mediated Synthesis of Carboxylic Anhydrides
377
2
420, 1050 cm ; Anal. Calcd for C H O : C, 47.06; H,5.92. Found C, 47.16;
1
1
H, 6.04.
4
6 3
ACKNOWLEDGMENT
This work was supported by a grant from the Korea Science and Engineering
Foundation (KOSEF) Grant (KRF-2003-015-C00338).
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