One-pot synthesis of azobenzene derivatives by oxidation of 2,3-dihydrobenzothiadiazines

Article abstract of DOI:10.1055/s-0033-1338587

An oxidative route to N-substituted sulfonamidic azobenzene derivatives is reported. A mechanism, based on a rationalization of previous findings, is proposed. This simple one-pot method could be adapted to the synthesis of a range of substituted sulfonylazobenzenes with potential applications in the pharmaceutical and industrial fields. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0033-1338587

962▌
PAPER
pOapnere-Pot Synthesis of Azobenzene Derivatives by Oxidation of 2,3-Dihydroben-
zothiadiazines
Oxidation of 2,3-Dihydrobenzothiadiazines
Giuseppe Cannazza,a Serena Perrone,b Francesca Rosato,b Lucia D’Accolti,c Carlo Parenti,a Luigino Troisi*b
a
Dipartimento di Scienze della Vita, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41125 Modena, Italy
b
Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, via Prov.le Lecce-Monteroni, 73100 Lecce, Italy
Fax +39(0832)298732; E-mail: luigino.troisi@unisalento.it
c
Dipartimento di Chimica, Università degli Studi di Bari ‘Aldo Moro’, via Orabona 4, 70126 Bari, Italy
Received: 21.11.2013; Accepted after revision: 23.12.2013
Since IDRA21 was in equilibrium with its imine interme-
Abstract: An oxidative route to N-substituted sulfonamidic azo-
diate A under the reaction conditions employed, it is likely
benzene derivatives is reported. A mechanism, based on a rational-
that the iminic bond can add a molecule of water to give
the corresponding carbinolamine B; the latter intermedi-
ization of previous findings, is proposed. This simple one-pot
method could be adapted to the synthesis of a range of substituted
sulfonylazobenzenes with potential applications in the pharmaceu- ate could be rapidly oxidized by one equivalent of
MCPBA, to carbonyl intermediate C.14 Since an excess of
tical and industrial fields.
MCPBA was used, the reaction conditions could lead to
oxidation of the amino group of intermediate C to give the
corresponding nitroderivative 2.15–17
Key words: azo compounds, sulfonamides, oxidation, ring open-
ing, imines
With the aim of isolating intermediate C, the oxidation re-
action of IDRA21 was carried out by using only one
equivalent of MCPBA. However, after 12 hours, LC-MS
analysis of the reaction mixture showed the formation of
a new product that did not correspond to C, together with
70% unreacted starting material 1, and trace amounts of
nitro-derivative 2. When the same reaction was carried
out with three equivalents of MCPBA, the new product
could be isolated. The product was identified as (E)-di-
azoderivative 3 (by NOESY measurement), and was prob-
ably derived from condensation of intermediate C with
compound 2 (Scheme 1). In this regard, it has been report-
ed that the treatment of aniline with hydrogen peroxide,
under SeO2 catalysis, leads to the formation of azoben-
zene.16,17 Since the sulfonamidic group ortho to the aro-
matic amino group of intermediate C increases the
reactivity of the amino group towards oxidative action of
peracid, catalysis might not be necessary. To confirm the
that the reaction also proceeded without added catalyst, 5-
chloro-2-aminobenzensulfonamide (4) was oxidized with
two equivalents of MCPBA under the same oxidation
conditions described above for IDRA21. This reaction af-
forded the corresponding (E)-6,6′-(diazene-1,2-di-
yl)bis(3-chlorobenzenesulfonamide) (5) in 22% yield
(Scheme 2), which is consistent with the mechanistic hy-
pothesis presented in Scheme 1.
The chemistry of substituted 1,2,4-benzothiadiazine 1,1-
dioxides is extensively studied because such compounds
represent an important scaffold in pharmaceutical chemis-
try that can be used as a basis for anticancer, nootropic,
antihypertensive, diuretic and antiviral agents.1–8
Recently, we demonstrated that some chiral derivatives of
2,3-dihydrobenzothiadiazines (e.g., 1) undergo rapid ra-
cemization at the stereogenic center C-3 in protic sol-
vents.9,10 It was suggested that the racemization
mechanism involves an imine intermediate with the dou-
ble bond at N-2 C-3 (A) or C-3 N-4, depending on the na-
ture of the substituents and on the pH of the racemization
solvent.11,12
More recently, our research group has developed a syn-
thetic strategy to oxidize cyclic imines to azodioxy-car-
bonyl compounds by the action of 3-chloroperoxybenzoic
acid (MCPBA).13 Starting from the proposed racemiza-
tion mechanism (Scheme 1), (±)-7-chloro-3-methyl-3,4-
dihydro-2H-1,2,4-benzothiadiazine
1,1-dioxide
(IDRA21, 1), was oxidized with MCPBA.
Depending on the amount of peracid used, different prod-
ucts were obtained, which underlines the conclusion that
the ratio IDRA21/MCPBA affects the oxidation reaction.
Particularly, the oxidation reaction of IDRA21 performed
with an excess of MCPBA (6 equiv.) at 0 °C in CH2Cl2
overnight, led only to the N-[(5-chloro-2-nitrophenyl)sul-
fonyl]acetamide (2), which was obtained in high yield
(99%). A possible mechanism that explains the formation
of 2 has been suggested (Scheme 1).
Due to the importance of azobenzene derivatives in both
pharmacology and industry,18–21 we extended the devel-
oped synthetic strategy to the preparation of a range of N-
substituted sulfonamidic azobenzenes. For this purpose, a
set of C-3 substituted 2,3-dihydrobenzothiadiazines were
reacted with three equivalents of MCPBA (Table 1).
Reagents 1, 6 and 7 (Table 1, entries 1–3) allowed us to
evaluate how the length of the C-3 aliphatic chain affects
the reactivity of benzothiadiazine in the oxidation reac-
tion. The yield of the azobenzene derivatives increased
SYNTHESIS 2014, 46, 0962–0966
Advanced online publication: 23.01.2014
DOI: 10.1055/s-0033-1338587; Art ID: SS-2013-T0740-OP
© Georg Thieme Verlag Stuttgart · New York
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X

PAPER
Oxidation of 2,3-Dihydrobenzothiadiazines
963
O
O
H
O
O
O
O
O
O
R
S
Cl
H2O
S
S
Cl
Cl
Cl
Cl
NH
N
N
OH
H
N
H
R
R
NH2
NH2
1
R = Me
A
B
[O]
R
O
S
N
O
H
O
O
O
NH2
S
Cl
N
R
C
H
N
N
[O]
H
R
N
S
Cl
R
O
O
O
O
S
[O]
N
O
H
3
O
N
O
2
Scheme 1 Suggested oxidation mechanism of IDRA21 to nitro- and/or azo-derivative
O
Table 1 Azobenzene Derivatives Obtained by Oxidation of 2,3-Di-
hydrobenzothiadiazines
O
S
Cl
O
NH2
O
Cl
S
O
O
O
N
[O]
NH2
S
Cl
N
R1
O
N
S
5
O
NH2
H
S
Cl
H2N
O
MCPBA ( 3 equiv)
CH2Cl2
R2
NH
R1
N
N
4
Cl
R2
Cl
R2
N
H
O
H
R1
N
1, 6–13
S
O
O
Scheme 2 Oxidation reaction of 5-chloro-2-aminobenzensulfon-
amide (4) to 5
O
3, 14–21
Entry Reagent R1
R2
Product Yield (%)
with the chain length, giving 19, 44 and 70% yield for
R1 = Me, Et and Pr, respectively (Table 1, entries 1–3).
Presumably, the greater electron-donating effect of the al-
iphatic group and better solubility of the starting material
with increasing C-3 chain length, positively influences the
efficiency of the reaction. In contrast, benzothiadiazine 8
did not react, probably due to the strong electron-with-
drawing effect of the trifluoromethyl group. This result
supports the hypothesis that electron-donating substitu-
ents on C-3 of the benzothiadiazine increase reactivity
(Table 1, entry 4). In addition, C-3 aryl-substituted benzo-
thiadiazines 9–12 reacted with MCPBA to give the corre-
sponding azobenzene derivatives 17–20 (Table 1, entries
5–8).
1
2
3
4
5
6
7
8
9
1
6
Me
H
H
H
H
H
H
H
H
Cl
3
14
15
16
17
18
19
20
21
19
44
70
–
Et
7
n-Pr
8
CF3
9
Ph
72
60
75
75
29
10
11
12
13
3-ClC6H4
2-MeOC6H4
4-HOC6H4
Me
Compounds 9–12 were chosen to assess the influence of
the C-3 aryl substituent on the reaction. Comparison of the
reaction yields revealed that the yield increased by using
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 962–966

964
G. Cannazza et al.
PAPER
ring closure of the commercially available 2-amino-4,5-dichloro-
benzenesulfonamide with acetaldehyde.1 The 1H and 13C NMR
spectra were recorded with a Bruker Avance 400 apparatus (400.13
aryl substituents with an electron-donating effect on the
C-3 of the benzothiadiazine (Table 1, entries 5–8). Fur-
thermore, the reaction yields shown in Table 1 indicate
that benzothiadiazines with a C-3 aryl substituent are
more reactive than those with C-3 alkyl substituents.
These results are consistent with previous studies regard-
ing enantiomerization rates of 2,3-dihydrobenzothiadi-
azines.9,10 Specifically, it was suggested that 3-
alkylbenzothiadiazines possess an enantiomerization bar-
rier higher than that of 3-phenyl-substituted benzothiadi-
azines. The resultant enantiomerization rates were
consistent with an interconversion mechanism that in-
volves the same imine intermediate with the double bond
between N-2 and C-3 proposed to account the formation
of azobenzene derivatives from benzothiadiazines.9,10 In
addition, a comparison between reagent 1 and 13 shows
that a chloro substituent on C-6 of the benzothiadiazine
does not affect the reaction yield (Table 1, entries 1 and 9).
1
and 100.62 MHz, for H and 13C, respectively) with CDCl3 as the
solvent and TMS as an internal standard (δ = 7.26 ppm for 1H spec-
tra; δ = 77.0 ppm for 13C spectra). The IR spectra were recorded
with a Digilab Scimitar Series FTS 2000 FTIR spectrophotometer.
LC–MS analyses were performed using an Agilent 1260 Infinity
Series HPLC system coupled to Agilent 6420 triple quadrupole de-
tector equipped with electrospray ionization (ESI). The electrospray
ionization [HRMS (ESI)] experiments were carried out in a hybrid
QqTOF mass spectrometer (PE SCIEX–QSTAR) equipped with an
ion-spray ionization source. MS (+) spectra were acquired by direct
infusion (5 μL·min–1) of a solution containing the appropriate sam-
ple (10 pmol·μL–1) dissolved in a solution of 0.1% AcOH, MeOH–
H2O (50:50) at the optimum ion voltage of 4800 V. The nitrogen gas
flow was set at 30 psi and the potentials of the orifice, the focusing
ring and the skimmer were kept at 30, 50 and 25 V relative to
ground, respectively. Melting points were determined with an Elec-
trothermal melting point apparatus and are uncorrected. TLC was
performed on Merck silica gel plates with F-254 indicator; viewing
was by UV light (254 nm). Column chromatography was performed
on silica gel (63–200 mm) using petroleum ether–EtOAc mixtures
as eluents.
In summary, a new synthetic pathway, based on the oxi-
dation of 2,3-dihydrobenzothiadiazines with MCPBA, to
produce sulfonamidic azobenzene derivatives was devel-
oped. 2,3-Dihydrobenzothiadiazines are easily prepared
in high yields (99%) by ring closure of commercially
available substituted benzenesulfonamides with selected
aldehydes, under catalytic acid conditions.1
N-Acetyl-5-chloro-2-nitrobenzenesulfonamide (2)
To an ice-cooled solution of 1 (233 mg, 1.0 mmol) in CH2Cl2 (10
mL) was added dropwise an excess of MCPBA (1478 mg, 6.0
mmol, 70%) in CH2Cl2 (10 mL) previously cooled in an ice bath.
The mixture was allowed to gradually warm to r.t., with stirring,
over 12 h. TLC and LC-MS analyses were used to monitor reaction
progress. When the reaction was complete, the solution was stirred
with excess powered anhydrous Na2CO3 until carbon dioxide evo-
lution ceased. After filtration, the mixture was concentrated in vac-
uo at r.t. to give pure 2.
Moreover, in accordance with our previously published
results, a reaction mechanism was proposed. This simple
one-pot method could be adapted to the synthesis of a
range of substituted sulfonylazobenzenes.
Because of the importance of azobenzenes,18–23 this syn-
thetic pathway seems to be an attractive strategy and an
economic approach to the preparation of products with
Yield: 275 mg (99%); yellow solid; mp 160−163 °C.
IR (KBr): 3160, 3101, 2990, 1600, 1550, 1350, 850 cm–1.
1H NMR (400.13 MHz, CDCl3): δ = 2.48 (s, 3 H, CH3), 7.63 (d,
potential in both pharmaceutical and industrial fields. In J = 9.0 Hz, 1 H, ArH), 7.98 (d, J = 9.0 Hz, 1 H, ArH), 8.06 (s, 1 H,
ArH), 9.25 (br s, 1 H, NH).
13C NMR (100.62 MHz, CDCl3): δ = 16.8, 125.4, 126.9, 133.0,
135.8, 138.1, 143.5, 165.7.
HRMS (ESI): m/z [M + H]+ calcd for C8H7ClN2O5S: 278.9842;
particular, azobenzene is widely used as a photoswitch in
biological systems to drive functional changes in peptides,
proteins, nucleic acids, lipids, and carbohydrates.21–23
Finally, it is noteworthy that azobenzene derivatives are
employed as prodrugs because they are rapidly metabo-
lized into the corresponding aromatic amino derivatives
by azoreducatase enzymes within the body.18 A common
system for measuring metabolism uses liver microsomes,
a subcellular fraction containing major drug-metabolizing
enzymes, including the cytochrome P450 family and fla-
vin monooxygenase. For this reason, the microsomial me-
found: 278.9840.
(E)-6,6′-(Diazene-1,2-diyl)bis(3-chlorobenzenesulfonamide) (5)
To an ice-cooled solution of 2-amino-5-chlorobenzenesulfonamide
(4; 206 mg, 1.0 mmol) in CH2Cl2 (10 mL) was added dropwise an
excess of MCPBA (493 mg, 2.0 mmol, 70%) in CH2Cl2 (10 mL)
previously cooled in an ice bath. The mixture was allowed to grad-
ually warm to r.t., with stirring, over 12 h. TLC and LC-MS analy-
ses were used to monitor reaction progress. The solution was then
tabolism of the obtained azobenzenes is under evaporated to dryness, in vacuo at r.t., to give the crude material,
which was purified by chromatography on silica gel (petroleum
ether–EtOAc, 50:50).
investigation and the results will be the object of another
publication.
Yield: 45 mg (22%); yellow solid; mp 198−200 °C.
IR (KBr): 3160, 3100, 2990, 1600, 1495, 1210, 840 cm–1.
All reactions involving air-sensitive reagents were performed under
1H NMR (400.13 MHz, acetone-d6): δ = 6.65 (dd, J = 9.0, 2.1 Hz,
2 H, ArH), 7.09 (s, 2 H, ArH), 7.50 (d, J = 9.0 Hz, 2 H, ArH), 8.70
(br s, 4 H, NH2).
13C NMR (100.62 MHz, CDCl3): δ = 115.8, 119.0, 122.7, 131.3,
132.6, 136.1.
HRMS (ESI): m/z [M + H]+ calcd for C12H11Cl2N4O4S2: 408.9599;
found: 408.9598.
an atmosphere of nitrogen in oven-dried glassware by using sy-
ringe/septum cap techniques. CH2Cl2 was distilled from calcium
hydride before use. Petroleum ether refers to the 40–60 °C boiling
fraction. 2-Amino-5-chlorobenzenesulfonamide (4) and m-chlo-
roperbenzoic acid (MCPBA) were of commercial grade (Aldrich)
and used without further purification. 2,3-Dihydrobenzothiadi-
azines 1, 6-12 were obtained by ring closure of 4 with a selected al-
dehyde, under catalytic acid conditions, following reported
synthetic protocols.1 Dihydrobenzothiadiazine (13) was obtained by
Synthesis 2014, 46, 962–966
© Georg Thieme Verlag Stuttgart · New York

PAPER
Oxidation of 2,3-Dihydrobenzothiadiazines
965
Azobenezene Derivatives 3 and 14–21; General Procedure
To an ice-cooled solution of 2,3-dihydrobenzothiadiazine 1 or 6–13
(1.0 mmol) in CH2Cl2 (10 mL) was added dropwise an excess of
MCPBA (739 mg, 3.0 mmol, 70%) in CH2Cl2 (10 mL) previously
cooled in an ice bath. The mixture was allowed to gradually warm
to r.t., with stirring, over 12 h. TLC and LC-MS analyses were used
to monitor reaction progress. The solution was then evaporated to
dryness, in vacuo at r.t., to give the crude material. The reaction
mixture was purified by chromatography on silica gel (petroleum
ether–EtOAc, 60:40).
1H NMR (400.13 MHz, acetone-d6): δ = 7.57–7.67 (m, 4 H, ArH),
7.84–7.94 (m, 10 H, ArH), 11.35 (br s, 2 H, NH).
13C NMR (100.62 MHz, acetone-d6): δ = 117.8, 123.3, 124.4, 128.5,
129.7, 129.9, 131.4, 131.6, 133.4, 133.5, 136.5, 155.7.
HRMS (ESI): m/z [M + H]+ calcd for C26H17Cl4N4O6S2: 684.9344;
found: 684.9346.
Compound 19
Yield: 254 mg (75%); light-yellow solid; mp 195−198 °C.
IR (KBr): 3160, 3072, 2974, 2944, 1703, 1600, 1584, 1518, 1489,
1417, 1190, 833 cm–1.
1H NMR (400.13 MHz, CDCl3): δ = 3.96 (s, 6 H, OCH3), 7.04 (d,
J = 8.2 Hz, 2 H, ArH), 7.14 (dt, J = 7.6, 0.8 Hz, 2 H, ArH), 7.54–
7.66 (m, 8 H, ArH), 7.86 (d, J = 2.1 Hz, 2 H, ArH), 8.24 (br s, 2 H,
NH).
13C NMR (100.62 MHz, CDCl3): δ = 56.8, 111.5, 117.0, 121.0,
122.2, 123.3, 124.0, 131.7, 132.5, 133.3, 133.6, 135.2, 155.9.
HRMS (ESI): m/z [M + H]+ calcd for C28H23Cl2N4O8S2: 677.0334;
found: 677.0336.
Compound 3
Yield: 46 mg (19%); light-yellow solid; mp 190−192 °C.
IR (KBr): 3212, 3108, 3076, 2984, 2943, 1744, 1582, 1462, 1380,
1288, 1175, 862 cm–1.
1H NMR (400.13 MHz, CDCl3): δ = 2.47 (s, 6 H, CH3), 7.33 (d,
J = 9.0 Hz, 2 H, ArH), 7.47 (dd, J = 9.0, 2.1 Hz, 2 H, ArH), 7.64 (d,
J = 2.1 Hz, 2 H, ArH), 8.95 (br s, 2 H, NH).
13C NMR (100.62 MHz, CDCl3): δ = 20.0, 115.6, 120.9, 122.6,
131.2, 132.5, 134.0, 162.1.
HRMS (ESI): m/z [M + H]+ calcd for C16H15Cl2N4O6S2: 492.9810;
found: 492.9812.
Compound 20
Yield: 243 mg (75%); light-yellow solid; mp 228–230 °C.
Compound 14
Yield: 114 mg (44%); light-yellow solid; mp 187−190 °C.
IR (KBr): 3169, 3105, 3076, 2924, 1608, 1586, 1498, 1414, 1374,
1287, 1114, 835 cm–1.
1H NMR (400.13 MHz, acetone-d6): δ = 6.96 (d, J = 8.9 Hz, 4 H,
ArH), 7.79–7.90 (m, 10 H, ArH), 9.32 (br s, 2 H, OH), 11.09 (br s,
2 H, NH).
13C NMR (100.62 MHz, acetone-d6): δ = 115.7, 118.6, 123.0, 123.9,
125.6, 132.0, 133.6, 133.9 (2C), 137.8, 161.9.
HRMS (ESI): m/z [M + H]+ calcd for C26H19Cl2N4O8S2: 649.0021;
found: 649.0020.
IR (KBr): 3211, 3110, 3076, 2984, 2945, 1744, 1580, 1463, 1420,
1290, 1175, 860 cm–1.
1H NMR (400.13 MHz, CDCl3): δ = 1.17 (t, J = 7.4 Hz, 6 H, CH3),
2.74 (q, J = 7.4 Hz, 4 H, CH2), 7.32 (d, J = 9.0 Hz, 2 H, ArH), 7.46
(dd, J = 9.0, 2.1 Hz, 2 H, ArH), 7.63 (d, J = 2.1 Hz, 2 H, ArH), 8.95
(br s, 2 H, NH).
13C NMR (100.62 MHz, CDCl3): δ = 9.1, 27.0, 116.7, 121.9, 123.6,
132.2, 133.5, 135.0, 163.2.
HRMS (ESI): m/z [M + H]+ calcd for C18H19Cl2N4O6S2: 521.0123;
found: 521.0125.
Compound 21
Yield: 81 mg (29%); light-yellow solid; mp 226−229 °C.
IR (KBr): 3076, 2963, 2923, 1697, 1577, 1515, 1472, 1428, 1370,
1291, 1165, 1114, 829 cm–1.
1H NMR (400.13 MHz, CDCl3): δ = 2.49 (s, 6 H, CH3), 7.52 (s, 2 H,
ArH), 7.77 (s, 2 H, ArH), 8.97 (br s, 2 H, NH).
13C NMR (100.62 MHz, CDCl3): δ = 21.8, 116.8, 120.4, 125.6,
131.5, 135.2, 138.9, 160.1.
HRMS (ESI): m/z [M + H]+ calcd for C16H13Cl4N4O6S2: 560.9031;
found: 560.9029.
Compound 15
Yield: 192 mg (70%); light-yellow solid; mp 180.5−182 °C.
IR (KBr): 3232, 3110, 3079, 2964, 2933, 2873, 1698, 1580, 1541,
1462, 1416, 1374, 1287, 1175, 899 cm–1.
1H NMR (400.13 MHz, CDCl3): δ = 1.04 (t, J = 7.4 Hz, 6 H, CH3),
1.63 (sext, J = 7.4 Hz, 4 H, CH2CH3), 2.62 (t, J = 7.4 Hz, 4 H,
COCH2), 7.34 (d, J = 9.0 Hz, 2 H, ArH), 7.47 (dd, J = 9.0, 2.1 Hz,
2 H, ArH), 7.66 (d, J = 2.1 Hz, 2 H, ArH), 8.98 (br s, 2 H, NH).
13C NMR (100.62 MHz, CDCl3): δ = 13.4, 18.6, 35.2, 116.8, 121.9,
123.6, 132.3, 133.5, 135.1, 162.5.
HRMS (ESI): m/z [M + H]+ calcd for C20H23Cl2N4O6S2: 549.0436;
Acknowledgment
We thank the University of Salento, PON 254/Ric. Potenziamento
del ‘Centro Ricerche Per La Salute Dell’Uomo E Dell’Ambiente’
Cod. PONa3_00334 and CINMPIS (Consorzio Interuniversitario
Nazionale Metodologie e Processi Innovativi di Sintesi) for finan-
cial support.
found: 549.0439.
Compound 17
Yield: 222 mg (72%); light-yellow solid; melts with decomposition.
IR (KBr): 3184, 2923, 2853, 1599, 1510, 1414, 1374, 1286,
827 cm–1.
1H NMR (400.13 MHz, acetone-d6): δ = 7.52–7.56 (m, 6 H, ArH),
7.85–7.90 (m, 10 H, ArH), 11.37 (br s, 2 H, NH).
References
(1) Battisti, U. M.; Jozwiak, K.; Cannazza, G.; Puia, G.; Stocca,
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Citti, C.; Troisi, L. ACS Med. Chem. Lett. 2012, 3, 25.
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Troisi, L. U.; Braghiroli, D.; Parenti, C.; Jozwiak, K. Bioorg.
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(3) Carrozzo, M. M.; Cannazza, G.; Pinetti, D.; Di Viesti, V.;
Battisti, U.; Braghiroli, D.; Parenti, C.; Baraldi, M. J. Neur.
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13C NMR (100.62 MHz, acetone-d6): δ = 117.7, 123.2, 124.5, 128.0,
130.0, 131.4, 131.6, 131.7, 133.3, 136.7, 157.2.
HRMS (ESI): m/z [M + H]+ calcd for C26H19Cl2N4O6S2: 617.0123;
found: 617.0125.
Compound 18
Yield: 206 mg (60%); light-yellow solid; mp 228−231 °C.
IR (KBr): 3176, 2963, 2923, 1696, 1574, 1515, 1472, 1427, 1370,
1291, 1164, 1114, 828 cm–1.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 962–966

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Synthesis 2014, 46, 962–966
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