Regioselective synthesis of novel N2- and N4- substituted 7-methylpyrazolo[4,5-e][1,2,4]thiadiazines

Article abstract of DOI:10.3390/11110827

The new compound 7-methylpyrazolo[4,5-e][1,2,4]thiadiazin-3(2H,4H)-one 1,1-dioxide (5) was synthesized and its novel mono N₂- or N ₄-substituted derivatives 6 and 7 were prepared by regioselective N-alkylation of 5 with different mol

Full text of DOI:10.3390/11110827

Molecules 2006, 11, 827-836
molecules
ISSN 1420-3049
http://www.mdpi.org
Full Paper
Regioselective Synthesis of Novel N2- and N4-Substituted 7-
Methylpyrazolo[4,5-e][1,2,4]thiadiazines
Xinyong Liu 1,*, Renzhang Yan 1, Niangen Chen 1, Wenfang Xu 1, Maria Teresa Molina 2 and
Salvador Vega 2
1
Institute of Medicinal Chemistry, School of Pharmacy, Shandong University, Jinan 250012, P.R.
China
2
Instituto de Quimica Medica (CSIC), c/Juan de la Cierva, 3, 28006 Madrid, Spain
* Author to whom correspondence should be addressed; Xinyong Liu, E-mail: xinyongl@sdu.edu.cn;
Tel: (+86)-531-8382005; Fax: (+86)-531-8382264
Received: 5 October 2006; in revised form: 22 October 2006/ Accepted: 23 October 2006 /
Published: 1 November 2006
Abstract: The new compound 7-methylpyrazolo[4,5-e][1,2,4]thiadiazin-3(2H,4H)-one
1,1-dioxide (5) was synthesized and its novel mono N2- or N4-substituted derivatives 6
and 7 were prepared by regioselective N-alkylation of 5 with different molar ratios of
NaH and alkyl halides. Based on the regioselective alkylation conditions found a facile
one-pot synthesis of N2,N4-disubstituted pyrazolo[4,5-e][1,2,4] thiadiazines 8 was
developed. The structures of the newly synthesized compounds were confirmed by IR,
1H-NMR, 13C-NMR and MS spectral analysis.
Keywords: Pyrazolothiadiazines, regioselectivity, synthesis, alkylation, one-pot reaction
Introduction
Benzo/heterothiadiazine derivatives have become of particular interest to chemists and biologists
because of their broad spectrum of biological activities and potential pharmacological applications. For
example, 1,2,4-benzothiadiazines, such as chlorothiazide and diazoxide, are widely used as diuretic
and antihypertensive drugs, respectively [1, 2]. Heterocycle-fused thiadiazine derivatives, such as

Molecules 2006, 11
828
pyrido-, pyrazino-, imidazo- and triazolothiadiazines, show unique potential for the treatment of
cerebro- and cardiovascular diseases, cognitive disorders, cancers, viral and bacterial infections [3-6].
We recently reported the design and synthesis of 2,4-disubstituted thieno[3,4-e][1,2,4] thiadiazine
derivatives (TTDs) [7], which selectively block HIV-1 replication at the reverse transcriptase step. The
lead compounds QM96639, QM96539 and QM96652 (Figure 1) showed highly potent activity and
selectivity against HIV-1 replication in cell culture at low concentration ranges (IC50 0.05-0.10µM)
[8,9].
Figure 1.
O O
S
O O
S
N
N
S
S
N
O
N
O
X
CN
QM96639 X=F
QM96539 X=Cl
QM96652
In continuation of our research, we decided to undertake a study of the pyrazole series, specifically
regarding the 7-methylpyrazolo[4,5-e][1,2,4]thiadiazines, because of the known thiophene-pyrazole
bioisosterism [10]. In this paper, we report the preparation of the new regioisomer 7-methylpyrazolo
[4,5-e][1,2,4]thiadiazine (5) and its novel mono N2- or N4- substituted derivatives 6 and 7 by
regioselective alkylation, as well as the one-pot synthesis of N2, N4-disubstituted 7-methylpyrazolo
[4,5-e][1,2,4] thiadiazines 8 (Figure 2).
Figure 2
O O
S
O O
S
O O
S
N
N
N
N
NH
N
N
N
R1
N
R1
N
O
N
O
N
O
H
R2
R2
7
8
6
Results and Discussion
7-Methylpyrazolo[4,5-e][1,2,4]thiadiazin-3(2H, 4H)-one 1,1-dioxide (5) was synthesized in a
similar manner to the thiophene and regioisomeric pyrazole series [7], by a route which started with
hydrazinolysis of ethyl 1-methyl-5-sulfamoylpyrazole-4-carboxylate (1), a commercially available
product, with hydrazine hydrate in refluxing ethanol, thus forming the hydrazide 2 in excellent yield.
Carboxy azide 3, which was obtained by the reaction of compound 2 with sodium nitrite in diluted
hydrochloric acid at ca. 10°C, was pure enough for use in the next ring closure step without further
purification. Thus, by refluxing compound 3 in anhydrous toluene, a classical Curtius rearrangement
took place through the intermediacy of isocyanate 4 to afford compound 5, a new regioisomer of 6-
methylpyrazolo[4,5-e][1,2,4]thiadiazin-3(2H, 4H)-one 1,1-dioxide prepared by our previous work [7].
1
13
(Scheme 1). Structural assignments for the ring system in 5 were based on its H- and C-NMR, IR
and MS spectral analysis.

Molecules 2006, 11
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The method used for the regioselective preparation of the new N2-substituted 7-methylpyrazolo-
[4,5-e][1,2,4]thiadiazine derivatives 6 paralleled that described in ref. [8], including deprotonation of
the 5 using one equivalent of sodium hydride in DMF solvent at a temperature below 5°C, and
followed by alkylation with one equivalent of alkyl halide at 80°C for 2-8 h, thus giving the mono N2-
substituted derivatives 6 (Scheme 2). The crude products were separated by flash column
chromatography and purified by recrystallization from ethanol in good yields (81-85%, Table 1).
Scheme 1.
SO2NH2
SO2NH2
SO2NH2
CON3
NaNO2/ H+
N
N
N2H2.H2O
EtOH
N
N
N
N
CO2C2H5
CO2NHNH2
1
2
3
O O
7
N
7a
SO2NH2
S
N
NH
Tol.
Reflux
6
1
2
N
N
5
4
4a
3
N=C=O
N
O
H
4
5
Scheme 2.
O O
O O
S
O O
S
S
N
N
N
NaH/R1CH2X(1:1)
NH
N
R1
N
N
N
N
DMF
N
H
O
N
H
O
N
H
O
R1
5
6
6'
Table 1. N2-substituted derivatives 6a-d and O-alkylated derivatives 6’a-d of 7-methyl-
pyrazolo[4,5-e][1,2,4]thiadiazin-3(2H,4H)-one 1,1-dioxide (5).
Yield ％
75
Entry
5
N2-/O-CH2R1
H
mp(°C)
216-218
175-177
192-194
220-222
187-188
215-216
238-240
246-248
224-227
δCH2
—
6a
benzyl
81
5.06
4.95
4.94
4.97
5.40
5.34
5.34
5.36
6b
4-Cl-benzyl
4-Br-benzyl
3-Cl-benzyl
benzyl
80
6c
83
6d
81
6’a
6’b
6’c
6’d
12
4-Cl-benzy
4-Br-benzyl
3-Cl-benzyl
14
13
16
Under these conditions compounds 6 were the predominant products, mainly due to the more
acidic nature of the hydrogen at the N2 position and the resulting easier deprotonation than the
hydrogen at the N4 position, which is caused by the strong electric withdraw effect by the sulfonyl
group. Meanwhile, the isomeric 3-O-alkylated pyrazolo[4,5-e][1,2,4]thiadiazine 6’ was observed as a

Molecules 2006, 11
830
side product in approximately 15% yields, which is attributed to the tautomerism between the nitrogen
anion and the carbonyl-oxygen anion. The O-alkylated isomers 6’a-d have not been reported so far. In
the 1H-NMR spectra, the chemical shifts of the O-CH2 groups are distinguished from that of mono N2-
or N4-alkylated derivatives, while linking with the same substituent (Table 1 and Table 2, e.g. benzyl
group, N2-CH2, δ 5.06; N4-CH2, δ 4.90; 3-O-CH2, δ 5.40).
During our ongoing research on the alkylation reaction of the compound 5, we used 2 equivalents
of base rather than only one, in order to perform double deprotonation of 5. Quenching of the disodium
salt with one equivalent of the electrophile, we observed complete regioselectivity of the reaction,
since only the N4-alkylated regioisomers 7 were produced, and none of N2-substituted compounds 6
was found. We speculate that the stronger nucleophilicity of N4 anion allowed a preferential N4
alkylation. We also deduced that the relatively high steric hindrance afforded by the 1-sulfonyl and 3-
carbony groups further disfavored the alkylation at N2 site.
Scheme 3.
O O
S
O O
S
N
N
NaH/R1CH2X(2:1)
DMF
NH
NH
N
N
N
H
O
N
O
R2
7a-d
5
The N4-alkylated product was confirmed by the chemical shift of the CH2 signal, and by means of
NOE experiments and HMBC sequences to establish long-distance proton/carbon correlations. It was
shown that the N4-CH2 correlated exclusively with the both quaternary carbon C-3 and C-4a, which is
different from the N2-CH2, that only correlated with quaternary carbon C-3. A series of N4-alkylated
derivatives 7a-d were prepared in high yield (80-86%) and the results were shown in Table 2.
Table 2. N4-substituted-7-methylpyrazolo[4,5-][1,2,4]thiadiazin-3(2H,4H)-one 1,1-dioxides.
Yield ％
Entry N4-CH2R2
Mp (°C) δCH2
7a
7b
7c
7d
benzyl
85
84
86
81
187-189
218-230
240-242
194-196
4.90
4.86
4.85
4.88
4-Cl-benzyl
4-Br-benzyl
3-Cl-benzyl
N2,N4-Disubstituted hetero[1,2,4]thiadiazines with different substituents are usually prepared by
stepwise alkylation, first at N2 and then at N4 [7,9]. Using to the aforementioned regioselective
alkylation method, N2,N4-disubstituted derivatives 8 were synthesized in a one-pot reaction, by
addition of two equivalents of NaH and one equivalent of R2CH2X first, followed by addition of one
equivalent of R1CH2X when the synthesis of intermediate 7 (monitored by TLC) was shown to be
finished. The crude products 8 were obtained and purified by recrystallization to give white solids in
ca. 80% yield (Scheme 4). A series of N2,N4-dialkylated derivatives 8a-d was prepared by this method

Molecules 2006, 11
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and are listed in Table 3. The structures of all synthesized compounds were confirmed by 1H- and 13C-
NMR, IR and MS spectroscopic analysis.
Scheme 4.
O O
S
O O
S
N
N
one-pot
NH
N
R1
N
N
N
H
O
N
O
R2
5
8a-d
Reagents: (1)NaH/R2CH2X (2:1); (2)R1CH2X(1eq)
Table 3. N2,N4-substituted-7-methylpyrazolo[4,5-e][1,2,4]thiadiazine-3(2H,4H)-one
1,1-dioxides 8a-d.
Yield ％
Entry
8a
N2-CH2R1
benzyl
N4-CH2R2
2-Br-benzyl
2-Cl-benzyl
mp(°C)
107-108
105-107
129-131
117-119
δN2-CH2 δN4-CH2
82
80
81
79
5.17
5.19
5.15
5.15
5.14
5.13
5.08
5.02
8b
8c
8d
benzyl
4-Cl-benzyl 2-Br-benzyl
4-Cl-benzyl 2-Cl-benzyl
Conclusions
In summary, we have synthesized the new regioisomer 7-methylpyrazolo[4,5-e][1,2,4]thiadiazin-
3(2H,4H)-one 1,1-dioxide 5 and studied its regioselective N-alkylation reactions. In the preparation of
N2-substituted pyrazolo[4,5-e][1,2,4]thiadiazines 6, we observed that formation of their O3-alkylated
isomers 6’ accompanied the reaction, which often went undetected and thus probably unreported
previously. We have also developed an efficient, regioselective alkylation at the N4 site of 5 by use of
a 2:1 molar ration of NaH and alkyl halide. The achieved conditions for the regioselective N-alkylation
were used to efficiently prepare the N2,N4-dialkylated derivatives 8 by a facile one-pot reaction. This
method can be used for the synthesis of other mono N2- and N4- or N2, N4-disubstituted heterocycle-
fused 1,2,4-thiadiazine derivatives.
Experimental Section
General
1
All melting points were determined on a micromelting point apparatus and are uncorrected. H-
NMR (600 MHz) and 13C-NMR (150 MHz) spectra were obtained on a Bruker Avance-600 instrument
in the indicated solvent. Chemical shifts are expressed in δ units and TMS as internal reference.
Infrared spectra (IR) were recorded with a Nexus 470FT-IR Spectrometer. Mass spectra were taken on
a LC Autosampler Device: Standard G1313A instrument. Flash column chromatography was
performed on column packed with silica gel 60 (230-400 mesh). Solvents were reagent grade and

Molecules 2006, 11
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when necessary, were purified and dried by standard methods. Concentration of the reaction solutions
involved the use of a rotary evaporator under reduced pressure.
Synthesis of 7-Methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine (5)
The synthesis was carried out in analogy to the preparation of the corresponding thieno[3,4-
e][1,2,4]thiadiazine and the regioisomeric 6-methylpyrazo[3,4-e][1,2,4]thiadiazine derivatives [7,8].
Recrystallization from ethanol gave a white solid. IR (KBr, cm-1): 3244, 3152 (NH); 3014 (Py-CH);
1
1692 (C=O); 1342, 1141 (SO2); H-NMR (DMSO-d6) δ: 11.49 (s, 1H, exchanged with deuterium by
13
D2O addition, NH); 7.40 (s, 1H, Py-CH); 3.94 (s, 3H, CH3); C-NMR (DMSO-d6) δ: 152.4 (C=O),
125.3 (C-5), 124.3 (C-4a), 123.4 (C-7a), 38.3 (CH3); MS (EI) m/z: 202.2 (M+); Anal. calcd for
C5H6N4O3S: C, 29.70; H, 2.99; N, 27.71; Found: C 29.76; H 3.03; N 27.66.
General Procedure for the Preparation of 2-Substituted-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-
e][1,2,4]thiadiazines 6a-d and 3-Substituted-7-methyl-1,1-dioxo-4H-pyrazolo[4,5-e][1,2,4]thiadia-
zines 6’a-d
To a solution of compound 5 (1 equiv.) in dry DMF (4 mL) was added sodium hydride (60%
dispersion in mineral oil, 1 equiv.) in portions, under an inert atmosphere (N2), while the temperature
was kept below 10°C. After stirring for 15 min, the alkyl halide (1 equiv.) was added dropwise. The
reaction mixture was stirred at room temperature for 20 min and at 30-50°C for 12-20 h (checked by
TLC). After the solvent was evaporated under reduced pressure, the products were separated by flash
column chromatography (1:3 ethyl acetate/cyclohexane) to give the compounds 6 and 6’ respectively,
which were purified by recrystallization from ethanol.
2-Benzyl-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine (6a) and 3-Benzyloxy-7-
methyl-1,1-dioxo-4H-pyrazolo[4,5-e][1,2,4]thiadiazine (6’a). Compound 5 was alkylated with benzyl
bromide at 30°C for 12h to give 6a and 6’a, which after purification gave white solids: 6a: IR (KBr,
cm-1): 3266 (NH); 1693 (C=O); 1328, 1197 (SO2); 1H-NMR (CDCl3) δ: 9.09 (s, 1H, NH), 7.20 (s, 1H,
PyH), 7.49 (d, 2H, J=7.31, PhH), 7.29-7.36 (m, 3H, PhH), 5.06 (s, 2H, NCH2), 4.13 (s, 3H, CH3); 13C-
NMR (CDCl3) δ: 150.3 (C=O), 135.4 (C-1’), 128.7, 128.5, 128.1, 125.0 (C-4a), 123.0 (C-5), 122.1 (C-
7a), 44.0 (N2-CH2), 39.0 (CH3); MS (EI): m/z 293.3 (M+1); 6’a: IR (KBr, cm-1): 3276 (NH);
1614(C=N); 1300, 1176 (SO2); 1H-NMR (DMSO-d6) δ: 12.33 (s, 1H, NH), 7.49 (s, 1H, PyH), 7.64
(dd, 1H, J=7.34Hz, J=1.85Hz, PhH), 7.55 (dd, 1H, J=7.73, J=1.16, PhH), 7.42-7.46 (m, 3H, PhH),
5.40 (s, 2H, NCH2), 3.98 (s, 3H, CH3); 13C-NMR (DMSO-d6) 151.7(C=N), 133.4(C-1’), 132.4, 131.4,
131.0, 129.7, 127.7, 125.5(C-4a), 123.9(C-5), 123.4(C-7a), 68.0(O-CH2), 38.4(CH3); MS (EI): m/z
292.3(M+).
2-(p-Chlorobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine (6b) and 3-(p-
chlorobenzyloxy)-7-methyl-1,1-dioxo-4H-pyrazolo[4,5-e][1,2,4] thiadiazine (6’b). Reaction of
compound 5 and 4-chlorobenzyl chloride at 50°C for 20 h gave compounds 6b and 6’b as white solids
1
after purification. 6b: IR (KBr, cm-1): 3225 (NH), 1682 (C=O), 1334, 1185 (SO2); H-NMR (DMSO-

Molecules 2006, 11
833
d6) δ: 11.37 (s, 1H, NH), 7.45 (s, 1H, PyH), 7.36-7.41 (m, 4H, PhH), 4.95 (s, 2H, NCH2), 4.03 (s, 3H,
13
CH3); C-NMR (DMSO-d6) δ: 148.8 (C=O), 135.6 (C-1’), 132.4, 129.9, 128.6, 125.7 (C-4a), 123.8
(C-5), 121.4 (C-7a), 42.3 (N2-CH2), 38.9 (CH3); MS(EI): m/z 327.3 (M+1); 6’b: IR (KBr, cm-1): 3242
1
(NH); 1610 (C=N); 1290, 1176(SO2); H- NMR (DMSO-d6) δ: 12.32 (s, 1H, NH), 7.53 (s, 1H, PyH),
7.48-7.51 (m, 4H, PhH), 5.34 (s, 2H, NCH2), 3.96 (s, 3H, CH3); 13C-NMR (DMSO-d6): 151.9 (C=N),
134.1 (C-1’), 133.5, 130.7, 128.8, 125.6 (C-4a), 124.0 (C-5), 123.6 (C-7a), 69.7 (O-CH2), 38.4 (CH3);
MS (EI): m/z 327.3 (M+1).
2-(p-Bromobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine (6c) and 3-(p-
Bromobenzyloxy)-7-methyl-1,1-dioxo-4H-pyrazolo[4,5-e][1,2,4] thiadiazine (6’c). Compound 5 and
4-bromobenzyl bromide at 30°C for 12 h gave after purification compounds 6c and 6’c as white solids.
6c: IR (KBr, cm-1): 3302 (NH); 1686 (C=O); 1364, 1197(SO2); 1H-NMR (DMSO-d6,) δ: 11.28 (s, 1H,
NH), 7.43 (s, 1H, PyH), 7.53 (d, 2H, J=7.91, PhH), 7.31 (d, 2H, J=7.70, PhH), 4.94 (s, 2H, NCH2),
4.03 (s, 3H, CH3); 13C-NMR (DMSO-d6) δ: 148.7 (C=O), 136.0 (C-1’), 131.4, 130.0, 125.6, 123.8 (C-
4a), 121.3 (C-5), 120.1 (C-7a), 42.3 (N2-CH2), 38.8 (CH3); MS (EI): m/z 373.1 (M+2), 371.2 (M+);
1
6’c: IR (KBr, cm-1): 3292(NH); 1605(C=N); 1274, 1173 (SO2); H-NMR (DMSO-d6) δ: 12.24 (s, 1H,
NH), 7.47 (s, 1H, PyH), 7.62 (d, 2H, J=7.33, PhH), 7.45 (d, 2H, J=7.44, PhH), 5.34 (s, 2H, NCH2),
3.96 (s, 3H, CH3); 13C-NMR (DMSO-d6) δ: 151.8 (C=N), 134.4 (C-1’), 131.6, 130.8, 125.5, 123.9 (C-
4a), 123.5 (C-5), 122.0 (C-7a), 69.7 (O-CH2), 38.3 (CH3); MS: m/z 373.1 (M+2), 371.2 (M+).
2-(m-Chlorobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine (6d) and 3-(m-
Chlorobenzyloxy)-7-methyl-1,1-dioxo-4H-pyrazolo[4,5-e][1,2,4]thiadiazine (6’d). Compound 5 and 3-
chlorobenzyl chloride at 50°C for 20h gave compounds 6d and 6’d as white solids after purification.
6d: IR (KBr, cm-1): 3223 (NH); 1678 (C=O); 1334, 1181 (SO2); 1H-NMR (DMSO-d6) δ: 11.39 (s, 1H,
13
NH), 7.45 (s, 1H, PyH), 7.31-7.40 (m, 4H, PhH), 4.97 (s, 2H, NCH2), 4.03 (s, 3H, CH3); C-NMR
(DMSO-d6) δ: 148.8 (C=O), 139.1 (C-1’), 133.1, 130.5, 127.7, 126.6, 125.7, 123.8 (C-4a), 121.3 (C-
5), 120.1 (C-7a), 42.4 (N2-CH2), 38.9 (CH3); MS: m/z 327.3 (M+1); 6’d: IR (KBr, cm-1): 3211 (NH),
1
1610 (C=N)；1312, 1174 (SO2); H-NMR (DMSO-d6) δ: 12.34 (s, 1H, NH), 7.50 (s, 1H, PyH), 7.59
(s, 1H, PhH), 7.45 (s, 3H, PhH), 5.36 (s, 2H, NCH2), 3.97 (s, 3H, CH3); 13C-NMR (DMSO-d6) δ: 151.9
(C=N), 137.6 (C-1’), 133.4, 130.7, 128.7, 128.4, 127.2, 125.6 (C-4a), 124.0 (C-5), 123.6 (C-7a), 69.6
(O-CH2), 38.4 (CH3); MS (EI): m/z 327.3 (M+1).
General Procedure for the Preparation of 4-Substituted-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e]
[1,2,4]thiadiazines (7a-d)
To a solution of compound 5 (1 equiv.) in dry DMF (4 mL) was added sodium hydride (60%
dispersion in mineral oil, 2 equiv.) in portions, under an inert atmosphere (N2) while the temperature
was kept below 10°C. After 60 min stirring, the alkyl halide (1 equiv.) was added dropwise. The
reaction mixture was stirred at room temperature for 20 min and at 40-60°C for 8-12h (checked by
TLC), and acidified with dilute hydrochloric acid (pH 4-6). The crude products obtained after the
solvent was evaporated under reduced pressure were then separated by flash column chromatography
using the indicated solvent system and purified by recrystallization from ethanol.

Molecules 2006, 11
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4-Benzyl-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine (7a). Compound 5 was
reacted with benzyl bromide at 30°C for 10 h to give 7a as a white solid after by flash column
chromatography separation (CH2Cl2/CH3OH 4:1) of the crude product and recrystallization. IR (KBr,
cm-1): 1694 (C=O); 1342, 1141 (SO2); 1H-NMR (DMSO-d6) δ: 7.18-7.29 (m, 5H, PhH), 7.09 (s, 1H,
PyH), 4.90 (s, 2H, NCH2), 3.83 (s, 3H, CH3); 13C-NMR (DMSO-d6) δ: 152.3 (C=O), 138 (C-1’), 128.4,
128.2, 127, 126.1 (C-4a), 125.0 (C-5), 123.2 (C-7a), 46.2 (CH2), 37.3 (CH3); MS (EI): m/z 292.3 (M+).
4-(p-Chlorobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine (7b). Compound 5
was reacted with 4-chlorobenzyl chloride at 50-60°C for 24 h to give 7b as a white solid after flash
column chromatography (CH2Cl2/CH3OH 4:1) of the crude product and recrystallization. IR (KBr,
cm-1): 1692 (C=O); 1327, 1135 (SO2); 1H-NMR (DMSO-d6) δ: 7.32-7.35 (m, 4H, PhH), 7.14 (s, 1H,
PyH), 4.86 (s, 2H, NCH2), 3.82 (s, 3H, CH3); 13C-NMR (DMSO-d6) δ: 152 .0 (C=O), 137.1 (C-1’),
131, 128.9, 128.3, 128.1 (C-4a), 125.0 (C-5), 123.0 (C-7a), 46.0 (CH2), 37.1 (CH3); MS (EI): m/z
327.3 (M+1).
4-(p-Bromobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine (7c). Compound 5
and 4-bromobenzyl bromide at 30°C for 10 h gave 7c as a white solid after purification of the crude
reaction product by flash column chromatography (CH2Cl2/CH3OH 3:1) and recrystallization. IR
(KBr, cm-1): 1693 (C=O); 1323, 1136 (SO2); 1H-NMR (DMSO-d6) δ: 7.20-7.47 (m, 4H, PhH), 7.14 (s,
1H, PyH), 4.85 (s, 2H, NCH2), 3.82 (s, 3H, CH3); 13C-NMR (DMSO-d6) δ: 152.2 (C=O), 138.3 (C-1’),
131.2, 129.1, 128.3, 125.4 (C-4a), 123.2 (C-5), 119.0 (C-7a), 47.2 (CH2), 37.3 (CH3); MS (EI): m/z
371.2 (M+1).
4-(m-Chlorobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine (7d). Compound
5 and 3-chlorobenzyl chloride at 50-60°C for 24 h gave 7d as a white solid after separation of the
crude product by flash column chromatography (CH2Cl2/CH3OH 4:1) and recrystallization. IR (KBr,
cm-1): 1695 (C=O); 1335, 1141 (SO2); 1H-NMR (DMSO-d6) δ: 7.22-7.33 (m, 4H, PhH), 7.18 (s, 1H,
PyH), 4.88 (s, 2H, NCH2), 3.83 (s, 3H, CH3); 13C-NMR (DMSO-d6) δ: 152 (C=O), 141.2 (C-1’), 132.8,
130.4, 128.0, 126.9, 126.8, 125.8 (C-4a), 125.7 (C-5), 123.2 (C-7a), 46.4 (CH2), 37.3 (CH3); MS (EI):
m/z 327.3 (M+1).
General Procedure for the Preparation of 2,4-Disubstituted 7-methyl-1,1,3-trioxo-2H,4H-pyrazolo
[4,5-e][1,2,4]thiadiazine Derivatives 8a-d
To a solution of compound 5 (1 equiv.) in dry DMF (4 mL/mmol) was added sodium hydride (60%
dispersion in mineral oil, 2 equiv.) in portions, under an inert atmosphere (N2) and keeping the
temperature below 10°C. After stirring for 60 min, the appropriate alkyl halide (R2CH2X, 1 equiv.)
was added dropwise. The reaction mixture was stirred at room temperature for 20 min and at 30-60°C
for 8-12h (checked by TLC), then the second alkyl halide (R1CH2X, 1 equiv.) was added dropwise.
Stirring of the mixture was continued for 12-20 h at 40-60°C, and then it was acidified (pH 4-6) with
dilute hydrochloric acid. After the solvent was evaporated under reduced pressure, the crude products
obtained were purified by recrystallization from ethanol to give 8a-d as white solids.

Molecules 2006, 11
835
2-Benzyl-4-(o-bromobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine
(8a).
Compound 5 was alkylated with 2-bromobenzyl bromide (30-40°C for 12h), then with benzyl bromide
1
(40-50°C for 12h) to give 8a. IR (KBr, cm-1): 1692 (C=O); 1324, 1192 (SO2); H-NMR (CDCl3) δ:
7.11 (s, 1H, PyH), 7.60 (d, 1H, J=7.87, PhH), 7.51 (d, 2H, J=7.46, PhH), 6.91 (d, 1H, J=7.57, PhH),
6.90-7.52 (m, 5H, PhH), 5.17 (s, 2H, NCH2), 5.14 (s, 2H, NCH2), 4.15 (s, 3H, CH3); 13C-NMR
(CDCl3) δ: 148.3 (C=O), 133.3 (C-1’), 135.3 (C-1”), 129.2, 128.3, 132.9, 129.2, 127.9, 127.8, 126.9,
125.1, 125.3 (C-4a), 122.9 (C-5), 122.2 (C-7a), 49.1 (N4-CH2), 44.6 (N2-CH2), 38.9 (CH3); MS (EI):
m/z 463.3 (M+2), 461.3 (M+).
2-Benzyl-4-(o-chlorobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadiazine
(8b).
Compound 5 was alkylated with 2-chlorobenzyl chloride (50-60°C for 12 h), then with benzyl bromide
1
(40-50°C for 12 h) to give 8b. IR (KBr, cm-1): 1691 (C=O), 1326, 1193 (SO2); H-NMR (CDCl3) δ:
6.95 (s, 1H, PyH), 7.13-7.51 (m, 9H, PhH), 5.19 (s, 2H, NCH2), 5.14 (s, 2H, NCH2), 4.15 (s, 3H, CH3);
13C-NMR (CDCl3) δ: 149.3 (C=O), 132.5 (C-1’), 135.3 (C-1”), 128.6, 128.3, 131.8, 129.7, 129.0,
127.9, 127.2, 170.0, 125.3 (C-4a), 124.9 (C-5), 120.0 (C-7a), 46.6 (N4-CH2), 44.5 (N2-CH2), 38.9
(CH3); MS (EI): m/z 417.4 (M+1).
2-(p-Chlorobenzyl)-4-(o-bromobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadia-
zine (8c). Compound 5 was alkylated with 2-bromobenzyl bromide (30-40°C for 12 h), then with 4-
chlorobenzyl chloride (50-60°C for 12 h) to give 8c. IR (KBr, cm-1): 1695 (C=O); 1331, 1192 (SO2);
1H-NMR (CDCl3) δ: 7.12 (s, 1H, PyH), 7.60 (dd, 1H, J=7.83, J=1.15, PhH), 6.88-7.47 (m, 7H, PhH),
5.15 (s, 2H, NCH2), 5.08 (s, 2H, NCH2), 4.14 (s, 3H, CH3); 13C-NMR (CDCl3) δ: 149.2 (C=O), 134.1
(C-1’), 137.3 (C-1”), 132.5, 131.6, 129.6, 129.5, 129.0 128.4, 128.1, 127.2, 126.9, 126.7, 125.2(C-4a),
125.0(C-5), 122.6 (C-7a), 46.6 (N4-CH2), 43.7 (N2-CH2), 38.9 (CH3); MS: m/z 497.3 (M+2), 495.2
(M+).
2-(p-Chlorobenzyl)-4-(o-chlorobenzyl)-7-methyl-1,1,3-trioxo-2H,4H-pyrazolo[4,5-e][1,2,4]thiadia-
zine (8d). Compound 5 was alkylated with 2-chlorobenzyl chloride (40-50°C for 20 h), then with 4-
chlorobenzyl chloride (50-60°C for 12 h) to give 8d. IR (KBr, cm-1): 1693 (C=O); 1331, 1193 (SO2);
1H-NMR (DMSO-d6) δ: 7.75(s, 1H, PyH), 7.50 (dd, 1H, J=7.86, J=1.23, PhH), 7.01 (dd, 1H, J=7.63,
J=1.25, PhH), 7.26-7.41 (m, 6H, PhH), 5.15 (s, 2H, NCH2), 5.02 (s, 2H, NCH2), 4.08 (s, 3H, CH3);
13C-NMR (DMSO-d6) δ: 148.8 (C=O), 133.0 (C-1’), 135.2 (C-1”), 132.1, 132.4, 129.9, 129.8, 129.5,
128.5, 127.7, 127.4, 126.3 (C-4a), 125.8 (C-5), 122.2 (C-7a), 47.2 (N4-CH2), 43.5 (N2-CH2), 39.1
(CH3); MS (EI): m/z 453.4 (M+2), 451.4 (M+).
Acknowledgements
The financial support by the National Natural Science Foundation of China (NSFC 30371686),
Ministry of Science and Technology of China for the key project of international cooperation
(2003DF000033), and NSF Shandong Province (Y2003C11), is gratefully acknowledged.

Molecules 2006, 11
836
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Sample Availability: Samples of the compounds are available from authors.
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