Site selectivity in reactions of hydrazonoyl halides with 2-amino-3-quinoxalinethiol: A new general access to functionalized 4H-1,3,4-thiadiazino-[5,6-b]quinoxalines

Article abstract of DOI:10.1080/104265090921100

The synthesis of various 2,4-disubstituted 4H-1,3,4-thiadiazino-[5,6-b] quinoxalines via reaction of hydrazonoyl halides with 2-amino-3-quinoxalinethiol in ethanol in the presence of sodium ethoxide is described. The structures of the reaction products we

Full text of DOI:10.1080/104265090921100

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Phosphorus, Sulfur, and Silicon
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Site Selectivity in Reactions
of Hydrazonoyl Halides With
2-Amino-3-quinoxalinethiol:
A New General Access to
Functionalized 4H-1,3,4-
Thiadiazino-[5,6-
b]quinoxalines
Ahmad Sami Shawali a , M. A. N. Mosselhi a &
Thoraya A. Farghaly a
a University of Cairo, Department of Chemistry ,
Giza, Egypt
Published online: 22 Aug 2006.
To cite this article: Ahmad Sami Shawali , M. A. N. Mosselhi & Thoraya A. Farghaly
(2005) Site Selectivity in Reactions of Hydrazonoyl Halides With 2-Amino-3-
quinoxalinethiol: A New General Access to Functionalized 4H-1,3,4-Thiadiazino-[5,6-
b]quinoxalines, Phosphorus, Sulfur, and Silicon and the Related Elements, 180:10,
2391-2402, DOI: 10.1080/104265090921100
To link to this article: http://dx.doi.org/10.1080/104265090921100
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Phosphorus, Sulfur, and Silicon, 180:2391–2402, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/104265090921100
Site Selectivity in Reactions of Hydrazonoyl Halides With
2-Amino-3-quinoxalinethiol: A New General Access to
Functionalized 4H-1,3,4-Thiadiazino-[5,6-b]quinoxalines
Ahmad Sami Shawali
M. A. N. Mosselhi
Thoraya A. Farghaly
Department of Chemistry, University of Cairo, Giza, Egypt
The synthesis of various 2,4-disubstituted 4H-1,3,4-thiadiazino-[5,6-b]quinoxalines
via reaction of hydrazonoyl halides with 2-amino-3-quinoxalinethiol in ethanol in
the presence of sodium ethoxide is described. The structures of the reaction products
1
13
were elucidated by chemical evidence and by their IR, H, C-NMR, and MS
spectra. The mechanism of the formation of the products is also discussed.
Keywords Heterocycles; hydrazonoyl halides; site selectivity; thiadiazinoquinoxalines
INTRODUCTION
Within the framework of our interest in regioselectivity in the reactions
of hydrazonoyl halides 1 with 1,2-aminothiols1−7 and in continuation
of our program aimed at developing new convenient approaches for
synthesis of fused heterocycles via utility of 1 as starting materials,8
we wish to report the results of our study of the reactions of 2-
amino-3-quinoxalinethiol 2 with five series of 1 (Scheme 1). Our
objective of such a study is to shed some light on the site selec-
tivity in such reactions as they can in principle lead to the for-
mation of 2,4-disubstituted 4H-1,3,4-thiadiazino[5,6-b]quinoxalines 3,
1,3-disubstituted 4H-1,2,4-triazino[5,6-b]quinoxalines 4 and/or 2,3-
disubstituted 4H-1,4-thiazino[5,6-b]quinoxalines 5(6) (Scheme 1). The
studied reactions were found to be site selective and provide new
general access to various 2,4-disubstituted 4H-1,3,4-thiadiazino[5,6-
b]quinoxalines 3. These latter heterocycles are expected to be of bi-
ological and technical interest since they are related to thiazolo[4,5-
b]quinoxalines whose 2-styryl derivatives were reported to be useful
Received September 7, 2004; accepted October 22, 2004.
Address correspondence to Ahmad Sami Shawali, University of Cairo, Department of
Chemistry, Faculty of Science, Giza, Egypt. E-mail: AS shawali@mail.com
2391

2392
A. S. Shawali et al.
SCHEME 1
as fluorescent dyes.9 Other fused quinoxalines were also reported to
be commercially important as agrochemicals, herbicides, fungicides,
antagonists, and anticiotics.9 Furthermore, our interest in developing
new access to functionalized 4H-1,3,4-thiadiazino[5,6-b]quinoxalines
results from the methods that we have reported that are either
multisteps or appear to be of limited appilicability. For example, a
literature search revealed that some of the 4H-1,3,4-thiadiazino[5,6-
b]quinoxalines 10A have been synthesized by the reaction of 2,3-
dichloroquinoxaline with benzoic thiohydrazide (Chart 1).10,11 Others,
such as 2-acylamino-4H-1,3,4-thiadiazino[5,6-b]quinoxalines 10B,
were prepared from 2-thiocarbamoylhydrazinoquinoxaline-4-oxides 11
via a N4-O-acylated intermediates 12 (Chart 1).12,13 The third method
was based on the reaction of 8-chloro-4-methyl-2-trifluromethyl-4H-
1,3,4-oxadiazino[5,6-b]quinoxaline 13 with phosphorus pentasulfide

Site Selectivity in Reactions
2393
CHART 1
to give 7-chloro-(1-methyl-2-trifluoro-acetylhydrazino)-2-thioxo-1,2-
dihydroquinoxaline 14, whose dehydration with sulfuric acid
in acetic acid afforded 8-chloro-4-methyl-2-trifluromethyl-4H-1,3,4-
thiadiazino[5,6-b]quinoxaline 10C (Chart 1).14
RESULTS AND DISCUSSION
The starting hydrazonoyl halides 115 and 2-amino-3-quinoxalinethiol
216 were prepared by literature methods. The reaction of 2 with each
of the hydrazonoyl halides 1A and 1E in ethanol in the presence of
sodium ethoxide gave, in each case, a single product whose mass spec-
trum and elemental analysis proved it to contain sulfur. This finding ex-
cludes the possible formation of the triazinoquinoxalines 4 (Scheme 1).
Similarly, the reactions of 2 with each of 1B–D yielded in each case a
single product. The IR spectra of the isolated products 3B–D revealed

2394
A. S. Shawali et al.
SCHEME 2
the presence of ester, amide, and acetyl carbonyl bands, respectively.
Their mass spectra displayed the molecular ion peaks in most cases as
the base peaks. In addition, the spectra revealed common peaks at m/z
values corresponding to the ion fragments A–G shown in Scheme 2.
This finding suggests that the fragmentation pattern of the molecular
ions of compounds prepared is as depicted in Scheme 2. On the basis
of such data, structures of type 5 and 6 were discarded (Scheme 1).
The 1H and 13C NMR of the isolated products and their elemental
analyses (see experimental section) were also found to be consistent
with structure 3. Further evidence for the assigned structure 3 and
in turn the proposed reaction pathway leading to it (Scheme 1) is sup-
ported by an alternate synthesis of 3Ea. Thus, reaction of 1,5-diphenyl-
3-mercaptoformazan 9Ea, commonly known as dithiazone, with ei-
ther 2,3-dichloroquinoxaline 717 or 2-amino-3-chloroquinoxaline 818 in
ethanol in the presence of triethylamine afforded in each case a product
that proved identical in all respect with 3Ea obtained from reaction of
2 with 1,5-diphenyl-3-chloroformazan 1Ea.

Site Selectivity in Reactions
2395
To account for the formation of 3 via the reaction of 1 with 2,
it is suggested, as depicted in Scheme 1, that the reactions started
with the formation of the respective thiohydrazonate esters I as in-
termediates which in turn undergo in situ deaminative cyclization
to give the respective 3. The first step is analogous to the forma-
tion of thiohydrazonates by reaction of hydrazonoyl halides with
thiols.19 The second cyclization step is reminiscent of the forma-
tion of 1H-1,2,4-triazolo[3,4-c]-1,2,4-triazoles via cyclization of ω-(3-
amino-1,2,4-triazol-4-yl)-ω-(phenylhydrazono)acetophenone20a and the
displacement of the amino group with the hydroxyl group during hy-
drolysis of 2-aminoquinoxalines.20b
In conclusion, compounds 3A–E represent important extensions in
the chemistry of ring-fused 1,3,4-thiadiazines. The availability of the
functional groups for further reactions offers the potential for novel
biologically active material or dyestuffs.
EXPERIMENTAL
All melting points were determined on an electrothermal Gallenkamp
apparatus and are uncorrected. Solvents were generally distilled and
dried by standard literature procedures prior to use. The IR spectra
were measured on a Pye-Unicam SP300 instrument in potassium bro-
1
mide discs. The H- and 13C-NMR spectra were recorded on a Varian
Mercury VXR-300 spectrometer (300 MHz for 1H and 75 MHz for 13C)
in CDCl3 or DMSO-d6 and the chemical shifts were related to that of
the solvent. The mass spectra were recorded on a GCMS-Q1000-EX
spectrometer; the ionizing voltage was 70 eV. Elemental analyses were
carried out by the Microanalytical Center of Cairo University, Giza,
Egypt. Dithiazone 9 was purchased from Fluka Chemical Company.
Hydrazonoyl halides 1 were prepared as previously described.15 The
reagents, 2-Amino-3-quinoxalinethiol 216, 2,3-dichloroquinoxaline 717
and 2-amino-3-chloroquinoxaline 818 were prepared by the literature
methods. The identification of compounds from different experiments
were secured by mixed m.p.s and superimposable IR spectra.
2,4-Disubstituted-4H-1,3,4-thiadiazino[5,6-b]quinoxalines
(3A–E)
General Procedure
A stirred sodium ethoxide solution, prepared from sodium metal
(0.06 g, 2.5 mmol) and absolute ethanol (15 cm3), was added to 2-
amino-3-quinoxalinethiol 2 (0.44 g, 2.5 mmol). After 10 min, the ap-
propriate hydrazonoyl halide 1 (2.5 mmol) was added and the reaction

2396
A. S. Shawali et al.
mixture was left overnight at room temperature while being stirred.
The solid that precipitated was filtered off, washed with H2O, dried, and
finally crystallized from the appropriate solvent to give the respective
2,4-disubstituted-4H-1,3,4-thiadiazino[5,6-b]quinoxaline 3. The com-
pounds 3A–E that were prepared are listed below with their physical
constants.
2,4-Diphenyl-4H-1,3,4-thiadiazino[5,6-b]quinoxaline (3Aa)
Yellow needles, (0.66 g, 75%); m.p. 206◦C (EtOH-Dioxane) (Lit. m.p.
196◦C)21; 1H NMR (DMSO-d6) δ 7.36–7.81 (m, ArH); 13C NMR (DMSO-
d6) δ 126.0, 126.39, 127.38, 127.72, 127.79, 128.03, 129.42, 129.68,
130.80, 131.66, 134.38, 138.86, 140.68, 143.02; MS m/z (%) 356 (M++
2, 6), 355 (M++ 1, 22), 354 (M+, 100), 326 (1), 277 (2), 250 (25), 223 (1),
218 (18), 148 (1), 134 (1), 122 (3), 118 (1), 103 (5), 90 (24), 77 (21), 76 (4);
Anal. Calcd. for C21H14N4S (354.44): C, 71.16; H, 3.73; N, 15.85; Found:
C, 71.02; H, 3.45; N, 15.58%.
2-Phenyl-4-(4-nitrophenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline (3Ab)
Orange solid (0.80 g, 80%), m.p. 232◦C (EtOH-Dioxane); 1H NMR
(DMSO-d6) δ 8.32 (d, J = 9 Hz, 2H, ArH), 8.01 (d, J = 9 Hz, 2H, ArH),
7.5–7.9 (m, 9H, ArH); MS m/z (%) 401 (M++ 2, 7), 400 (M++ 1, 25), 399
(M+, 100), 371 (1), 352 (14), 322 (1), 269 (5), 250 (29), 219 (2), 206 (17),
191 (8), 176 (8), 164 (2), 160 (8), 152 (2), 146 (1), 134 (8), 129 (5), 122
(17), 90 (65), 77 (25), 76 (30); Anal. Calcd. for C21H13N5O2S (399.43): C,
63.15; H, 3.28; N, 17.53; Found: C, 63.02; H, 3.20; N, 17.25%.
Ethyl 4-Phenyl-4H-1,3,4-thiadiazino[5,6-b]quinoxaline-
2-carboxylate (3Ba)
Yellow needles (0.74 g, 85%), m.p. 204◦C (EtOH-Dioxane); IR (KBr) ν
1
1707 cm−1; H NMR (DMSO-d6) δ 1.26 (t, J = 7 Hz, 3H, CH3), 4.29
(q, J = 7 Hz, 2H, CH2), 7.28–7.63 (m, 9H, ArH); 13C NMR (DMSO-d6)
δ 13.83, 62.65, 126.25, 126.72, 127.09, 127.66, 127.92, 128.86, 129.17,
129.99, 139.65, 139.92, 141.50, 142.30, 143.07, 159.94; MS m/z (%) 352
(M++ 2, 8), 351 (M++ 1, 12), 350 (M+, 100), 349 (14), 322 (4), 277 (27),
251 (21), 225 (6), 218 (66), 207 (14), 166 (10), 148 (3), 134 (3), 121 (2),
117 (3), 91 (51), 77 (100), 76 (8); Anal. Cacld. for C18H14N4O2S (350.40):
C, 61.71; H, 4.03; N, 15.99; Found: C, 61.70; H, 4.00; N, 16.09%.

Site Selectivity in Reactions
2397
Ethyl 4-(4-Nitrophenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline-2-carboxylate (3Bb)
Yellow solid (0.82 g, 82%), m.p. 270◦C (EtOH-Dioxane); IR (KBr) ν 1751
1
cm−1; H NMR (DMSO-d6) δ 1.29 (t, J = 7 Hz, 3H, CH3), 4.33 (q, J =
7 Hz, 3H, CH2), 7.42–7.70 (m, 4H, ArH), 7.85 (d, J = 8 Hz, 2H, ArH),
8.35 (d, J = 9 Hz, 2H, ArH); MS m/z (%) 397 (M+, + 2, 10), 396 (M++ 1,
28), 395 (M+, 100), 394 (17), 367 (9), 322 (16), 296 (5), 266 (4), 250 (19),
218 (10), 164 (93), 149 (2), 134 (4), 122 (4), 102 (7), 90 (23), 76 (6); Anal.
Calcd. for C18H14N5O4S (395.40): C, 54.63; H, 3.31; N, 17.71; Found: C,
54.50; H, 3.05; N, 17.92%.
Ethyl 4-(4-Methylphenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline-2-carboxylate (3Bc)
Yellow needles (0.78 g, 86%), m.p. 200◦C (EtOH); IR (KBr) 1712 cm−1
;
1H NMR (DMSO-d6) δ 1.39 (t, J = 7 Hz, 3H), 1.54 (s, 3H, CH3), 4.38
(q, J = 7 Hz, 2H, CH2), 7.26–7.46 (m, 4H, ArH); 7.49 (d, J = 8 Hz, 2H,
ArH), 7.52 (d, J = 8 Hz, 2H, ArH); MS m/z (%) 366 (M++ 2, 7), 365 (M++
1, 19), 364 (M+, 71), 291 (23), 264 (25), 234 (4), 232 (100), 134 (7), 129
(10), 122(10), 105 (13), 104 (29), 102 (27), 91 (87), 77 (48); Anal. Calcd.
for C19H16N4O2S (364.43): C, 62.62; H, 4.43; N, 15.37; Found: C, 62.41;
H, 4.15; N, 15.32%.
Ethyl 4-(4-Chlorophenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline-2-carboxylate (3Bd)
Orange crystals (0.77 g, 80%), m.p. 198◦C (EtOH); IR (KBr) ν 1710 cm−1
;
1H NMR (DMSO-d6) δ 1.26 (t, J = 7 Hz, 2H, CH3), 4.32 (q, J = 7 Hz,
2H, CH2), 7.09 (d, J = 7 Hz, 2H, ArH), 7.45 (d, J = 8 Hz, 2H, ArH),
7.57–7,64 (m, 4H, ArH); MS m/z (%) 386 (M++ 2, 55), 385 (M++ 1, 29),
384 (M+, 100), 311 (37), 254 (17), 252 (50), 250 (93), 218 (40), 161 (22),
147 (7), 133 (16), 122 (7), 111 (23), 105 (12), 102 (29), 91 (10), 90 (57),
77 (11), 76 (15); Anal. Calcd. for C18H13ClN4O2S (384.85): C, 56.18; H,
3.40; N, 14.56; Found: C, 56.57; H, 3.39; N, 14.32%.
N-Phenyl 4-Phenyl-4H-1,3,4-thiadiazino[5,6-b]quinoxaline-
2-carboxamide (3Ca)
Yellow solid, (0.79 g, 80%), m.p. 220◦C (EtOH-Dioxane); IR (KBr) ν 3379,
1681 cm−1; 1H NMR (DMSO-d6) δ 11.6 (s, 1H, NH), 7.34–7.83 (m, 14H,
ArH); MS m/z (%) 400 (M++ 2, 9), 398 (M++ 1, 27), 397 (M+, 100), 277
(37), 259 (27), 251 (16), 233 (8), 225 (2), 218 (45), 148 (2), 134 (2), 117 (2),

2398
A. S. Shawali et al.
120 (10), 104 (4), 91 (14), 77 (68), 76 (6); Anal. Calcd. for C22H15N5OS
(397.46): C, 66.50; H, 3.78; N, 17.63; Found: C, 66.21; H, 4.08; N, 17.30%.
N-Phenyl 4-(4-Nitrophenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline-2-carboxamide (3Cb)
Orange solid, (0.90 g, 81%), m.p. 180◦C, IR (KBr) ν 3432, 1668 cm−1
;
1H NMR (DMSO-d6) δ 7.70–7.15 (m, 4H, ArH), 7.27 (d, J = 8 Hz, 2H,
ArH), 7.29 (d, J = 8 Hz, 2H, ArH), 12.08 (s, 1H, NH); MS m/z (%) 444
(M+, + 2, 6), 443 (M++ 1, 6), 442 (M+, 79), 413 (1), 322 (21), 296 (8),
276 (27), 267 (1), 210 (22), 206 (11), 164 (5), 146 (4), 134 (5), 122 (7),
120 (34), 119 (14), 102 (23), 90 (50), 77 (100), 76 (17); Anal. Calcd. for
C22H16N6O3S (442.46): C, 59.72; H, 3.19; N, 18.99; Found: C, 59.31; H,
3.45; N, 18.78%.
N-Phenyl 4-(4-Chlorophenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline-2-carboxamide (3Cd)
Yellow solid (0.88 g, 82%), m.p. 274◦C (Dioxane); IR (KBr) ν 3379,
1
1681 cm−1; H NMR (DMSO-d6) δ 7.35 (d, J = 8 Hz, 2H, ArH), 7.48–
7.67 (m, 4H, ArH), 7.75 (d, J = 8 Hz, 2H, ArH), 10.12 (s, 1H, NH);
13C NMR (DMSO-d6) δ 121.09, 124.59, 126.76, 127.10, 127.73, 127.95,
128.45, 128.55, 130.00, 131.21, 135.22, 137.07, 139.56, 139.99, 140.05,
142.29, 143.55, 158.13; MS m/z (%) 434 (M+, + 2, 23), 433 (M++ 1, 41),
432 (M+, 30), 431 (100), 430 (12), 311 (37), 285 (17), 255 (5), 250 (53),
218 (26), 151 (2), 147 (3), 137 (6), 120 (21), 111 (13), 102 (13), 90 (45), 77
(70), 76 (6); Anal. Calcd. for C22H14ClN5OS (431.91): C, 61.18; H, 3.27;
N, 16.21; Found: C, 61.63; H, 3.44; N, 16.20%.
2-Acetyl-4-phenyl-4H-1,3,4-thiadiazino[5,6-b]quinoxaline (3Da)
Orange crystals (0.72 g, 90%), m.p. 230◦C (EtOH-Dioxane); IR (KBr) ν
1
1681 cm−1; H NMR (DMSO-d6) δ 2.34 (s, 3H, COCH3), 7.45–7.63 (m,
9H, ArH); MS m/z (%) 322 (M++ 2, 7), 321 (M++ 1, 22), 320 (M+, 100),
305 (11), 277 (65), 251 (22), 225 (2), 218 (46), 160 (2), 148 (2), 134 (2),
129 (3), 120 (1), 118 (3), 102 (20), 90 (34), 77 (78), 76 (15); Anal. Calcd.
for C17H12N4OS (320.38): C, 63.73; H, 3.78; N, 17.43; Found: C, 63.50;
H, 3.43; N, 17.34%.
2-Acetyl-4-(4-nitrophenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline (3Db)
Yellow solid (0.78 g, 85%), m.p. >300◦C (Dioxane); IR (KBr) ν 1665
1
cm−1; H NMR (DMSO-d6) δ 2.40 (s, 3H, COCH3), 7.14–7.84 (m, 4H,
ArH), 7.81 (d, J = 9 Hz, 2H, ArH), 8.13 (d, J = 9 Hz, 2H, ArH), MS

Site Selectivity in Reactions
2399
m/z (%) 367 (M+, + 2, 7), 366 (M++ 1, 25), 365 (M+, 9), 236 (9), 206 (9),
196 (91), 174 (9), 162 (9), 160 (100), 148 (9), 134 (23), 122 (6), 120 (9),
105 (22), 102 (9), 91 (9), 78 (10), 76 (3); Anal. Calcd. for C17H11N5O3S
(365.39): C, 55.89; H, 3.01; N, 19.18; Found: C, 55.71; H, 2.89; N, 19.00%.
2-Acetyl-4-(4-methylphenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline (3Dc)
Yellow solid, 0.71 g, 85%; m.p. 190◦C (Ethanol); IR (KBr) ν 1689 cm−1
;
1H NMR (DMSO-d6) δ 2.00 (s, 3H, ArCH3), 2.35 (s, 3H, COCH3), 6.89–
7.13 (m, 4H, ArH), 7.21 (d, J = 8 Hz, 2H, ArH), 7.41 (d, J = 8 Hz, 2H,
ArH); MS m/z (%) 336 (M++ 2, 7), 335 (M++ 1, 23), 334 (M+, 87), 320
(27), 305 (4), 291 (47), 277 (25), 265 (19), 239 (3), 205 (12), 161 (22), 149
(8), 134 (4), 121 (13), 132 (28), 118 (19), 106 (87), 105 (40), 104 (27), 91
(100), 77 (92), 76 (21); Anal. Calcd. for C18H14N4OS (334.40): C, 64.65;
H, 4.22; N, 16.75; Found: C, 64.41; H, 4.27; N, 16.75%.
2-Acetyl-4-(4-chlorophenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline (3Dd)
Brown solid (0.80 g, 90%; m.p. 208◦C (Ethanol-dioxane); IR (KBr) ν
1
1689 cm−1; H NMR (DMSO-d6) δ 2.36 (s, 3H, COCH3), 7.39–7.50 (m,
4H, ArH), 7.56 (d, J = 7 Hz, 2H, ArH), 7.66 (d, J = 7 Hz, 2H, ArH); MS
m/z (%) 357 (M++ 3, 7), 356 (M++ 2, 29), 355 (M++ 1, 20), 354 (M+,
84), 339 (14), 311 (38), 285 (16), 277 (16), 255 (5), 250 (71), 218 (27),
152 (96), 148 (5), 137 (10), 111 (32), 125 (20), 102 (38), 90 (100), 77 (12),
76 (32); Anal. Calcd. for C17H11ClN4OS (354.82): C, 57.55; H, 3.12; N,
15.79; Found: C, 57.10; H, 3.41; N, 15.52%.
2-Acetyl-4-(3-methylphenyl)-4H-1,3,4-thiadiazino[5,6-
b]quinoxaline (3De)
Red solid (0.65 g, 78%), m.p. 218◦C (Ethanol-dioxane); IR (KBr) ν
1
1672 cm−1; H NMR (DMSO-d6) δ 2.32 (s, 3H, ArCH3), 2.38 (s, 3H,
COCH3), 7.32–7.63 (m, 8H, ArH); MS m/z (%) 336 (M+, + 2, 7), 335 (M+
+ 1, 22), 334 (M+, 100), 319 (8), 291 (35), 277 (8), 265 (7), 235 (1), 232
(21), 134 (91), 122 (1), 104 (3), 91 (7), 77 (3), 76 (2); Anal. Calcd. for
C18H14N4OS (334.40): C, 64.65; H, 4.22; N, 16.75; Found: C, 64.23; H,
4.00; N, 16.34%.
2-Acetyl-4-(3-chlorophenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline (3Df)
Yellow solid (0.71 g, 80%); m.p. 210◦C (Ethanol-dioxane); IR (KBr) ν
1
1681 cm−1; H NMR (DMSO-d6) δ 2.36 (s, 3H, COCH3), 7.39–7.73 (m,

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A. S. Shawali et al.
8H, ArH); MS m/z (%) 358 (M++ 4, 2), 357 (M++ 3, 7), 356 (M++ 2,
27), 355 (M++ 1, 15), 354 (M+, 64), 339 (12), 311 (39), 285 (9), 259 (2),
277 (12), 250 (36), 218 (25), 148 (5), 134 (5), 122 (9), 111 (32), 102 (41),
90 (83), 75 (100); Anal. Calcd. for C17H11ClN4OS (354.82): C, 57.55; H,
3.12; N, 15.79; Found: C, 57.30; H, 3.00; N, 15.30%.
2-Acetyl-4-(3-nitrophenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline (3Dg)
Orange crystals (0.69 g, 75%); m.p. 220◦C (Ethanol-dioxane); IR (KBr)
ν 1687 cm−1; 1H NMR (DMSO-d6) δ 2.39 (s, 3H, COCH3), 7.38–8.55 (m,
8H, ArH); 13C NMR (DMSO-d6) δ 23.96, 120.5, 122.03, 126.76, 127.20,
128.45, 130.11, 132.07, 138.56, 139.14, 140.08, 142.12, 147.79, 192.37;
MS m/z (%) 367 (M+, + 2, 7), 366 (M++ 1, 21), 365 (M+, 100), 322 (18),
276 (19), 231 (2), 218 (12), 206 (14), 175 (3), 162 (9), 147 (9), 134 (230),
122 (8), 102 (45), 90 (77), 76 (3); Anal. Calcd. for C17H11N5O3S (365.39):
C, 55.89; H, 3.01; N, 19.18; Found: C, 55.92; H, 3.33; N, 18.78%.
2-Acetyl-4-(4-methoxyphenyl)-4H-1,3,4-thiadiazino-
[5,6-b]quinoxaline (3Dh)
Orange crystals (0.70 g, 80%); m.p. 190◦C (Ethanol); IR (KBr) ν
1
1681 cm−1; H NMR (DMSO-d6) δ 2.49 (s, 3H, COCH3), 3.73 (s, 3H,
OCH3), 7.04 (d, J = 7 Hz, 2H, ArH), 7.33–7.59 (m, 4H, ArH), 7.46 (d,
J = 7 Hz, 2H, ArH); MS m/z (%) 352 (M+, + 2, 20), 351 (M++ 1, 24),
350 (M+, 83), 307 (22), 281 (37), 266 (100), 250 (31), 148 (13), 134 (17),
122 (36), 107 (8), 90 (28), 78 (41), 77 (21), 76 (17); Anal. Calcd. for
C18H14N4O2S (350.40): C, 61.74; H, 4.03; N, 15.99; Found: C, 61.90; H,
3.70; N, 15.78%.
2-Phenylazo-4-(phenyl)-4H-1,3,4-thiadiazino[5,6-b]quinoxaline
(3Ea)
Red crystals (0.76 g, 80%), m.p. > 300◦C (EtOH-Dioxane) (Lit. m.p.
1
313◦C)21; H NMR (DMSO-d6) δ 7.38–7.87 (m, ArH); MS m/z (%) 384
(M+, + 2, 2), 383 (M++ 1, 8), 382 (M+, 30), 354 (4), 277 (8), 251 (2),
223 (2), 218 (12), 105 (16), 102 (4), 77 (100) 76 (4); Anal. Calcd. for
C21H14N6S (382.45): C, 65.95; H, 3.69; N, 21.97; Found: C, 65.96; H,
3.87; N, 21.35%.
Alternate Synthesis of 3Ea
A stirred sodium ethoxide solution prepared from sodium metal (0.06 g,
2.5 mmol) and absolute ethanol (15 cm3) was added to dithiazone 9Ea

Site Selectivity in Reactions
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(0.64 g, 2.5 mmol) and after 5 min was added 2,4-dichloroquinoxaline
7 (0.50 g, 2.5 mmol) and the reaction mixture was refluxed for 5 h
and cooled. The solid that precipitated was filtered off, washed with
water, dried, and finally crystallized from ethanol-dioxane mixture
to give the respective 2-phenylazo-3-phenyl-4H-1,3,4-thiadiazino[5,6-
b]quinoxaline 3Ea21, which was found identical in all respects with the
product 3Ea prepared above from 1Ea and 2.
Repetition of the above procedure using 2-chloro-3-aminoquinoxaline
8 in place of 7 and work up the reaction mixture also yielded 3Ea.
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