Facile synthesis of 2H-1,4-Benzothiazin-3(4H)-ketoximes and 2H-1,4-Benzoselenazin-3(4H)-ketoximes promoted by SmI2

Article abstract of DOI:10.1081/SCC-120024734

2H-1,4-Benzothiazin-3(4H)-ketoximes and 2H-1,4-benzoselenazin-3(4H)-ketoximes were synthesized by the reductive cyclization of bis(o-nitrophenyl) disulfides or diselenides with aromatic or aliphatic β-nitroethylenes using SmI₂ in moderate to good yields under mild conditions.

Full text of DOI:10.1081/SCC-120024734

Synthetic Communications
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ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Facile Synthesis of 2H-1,4-Benzothiazin-3(4H)-
ketoximes and 2H-1,4-Benzoselenazin-3(4H)-
ketoximes Promoted by SmI2
Xiaoliang Xu & Yongmin Zhang
To cite this article: Xiaoliang Xu & Yongmin Zhang (2003) Facile Synthesis of 2H-1,4-
Benzothiazin-3(4H)-ketoximes and 2H-1,4-Benzoselenazin-3(4H)-ketoximes Promoted by SmI2 ,
Synthetic Communications, 33:20, 3537-3543, DOI: 10.1081/SCC-120024734
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 20, pp. 3537–3543, 2003
Facile Synthesis of 2H-1,4-Benzothiazin-3(4H )-
ketoximes and 2H-1,4-Benzoselenazin-3(4H )-
ketoximes Promoted by SmI2
Xiaoliang Xu1 and Yongmin Zhang1,2,
*
1Department of Chemistry, Zhejiang University
(Campus Xixi), Hangzhou, P.R. China
2State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences, Shanghai, P.R. China
ABSTRACT
2H-1,4-Benzothiazin-3(4H )-ketoximes and 2H-1,4-benzoselenazin-
3(4H )-ketoximes were synthesized by the reductive cyclization of
bis(o-nitrophenyl) disulfides or diselenides with aromatic or aliphatic
b-nitroethylenes using SmI2 in moderate to good yields under mild
conditions.
*Correspondence: Yongmin Zhang, Department of Chemistry, Zhejiang
University (Campus Xixi), Hangzhou, 310028, P.R. China; State Key
Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai, 200032, P.R. China;
Fax: 86-571-8807077; E-mail: yminzhang@mail.hz.zj.cn.
3537
DOI: 10.1081/SCC-120024734
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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3538
Xu and Zhang
The biological and pharmacological importance of 2H-1,4-
benzothiazin-3(4H )-one derivatives, which can be used as efficient
tranquilizers, angiotensin converting enzyme inhibitors, aldose
reductase inhibitors and also showed antibacterial and antifugal activ-
ities, has led to important synthetic efforts in the past decades.[1]
Among these compounds, the substituted 2H-1,4-benzothiazin-3(4H )-
ones are well known in the literatures and several methods for their
synthesis have been reported by many chemists including our
group.[1a,2] However, upon checking the literature, only one example
reported the synthesis of 2H-1,4-benzothiazin-3(4H )-ketoximes.[1e] The
reason may be that 2H-1,4-benzothiazin-3(4H )-ones cannot react with
hydroxyamine under usual conditions due to the low reactivity of their
carbonyl groups. As far as 2H-1,4-benzoselenazin-3(4H )-ketoximes
are concerned, no literature has ever been reported for their synthesis.
Here we wish to describe a convenient method for the preparation
of 2H-1,4-benzothiazin-3(4H )-ketoximes and 2H-1,4-benzoselenazin-
3(4H )-ketoximes promoted by SmI2.
Samarium diiodide[3] is an exceedingly reliable, mild, neutral, selective,
and versatile single electron transfer reagent and its use in organic
synthesis has been especially advantageous for ring closure reactions,
carbon–carbon bond formation and stereoselective reactions. Its appli-
cation in organic synthesis has been well documented in the past dec-
ades.[4] The reduction of nitro groups and reductive cleavage of S-S, Se-Se
bonds by SmI2 have been studied extensively.[5] Our group have reported
the simultaneous reduction of two functional groups to form an active
trivalent samarium species, which has been successfully applied in the
synthesis of heterocyclic compounds.[2i,6] In order to extend the applica-
tion of this active trivalent samarium species, we used SmI2 to react with
aromatic or aliphatic b-nitroethylenes and the corresponding products
2H-1,4-benzothiazin-3(4H )-ketoximes
and
2H-1,4-benzoselenazin-
3(4H)-ketoximes were readily obtained in moderate to good yields
under mild conditions (Sch. 1).
When 0.5 equivalents of bis(o-nitrophenyl) disulfides or diselenides 1
were treated with 7 equivalents of SmI2 in THF at room temperature, the
deep blue color of SmI2 vanished within 5 min and another substrate
b-nitroethylenes 2 were added. The desired products 2H-1,4-benzothiazin-
3(4H)-ketoximes or 2H-1,4-benzoselenazin-3(4H)-ketoximes
obtained in moderate to good yields.[7]
3 were
Table 1 summarizes our results. All the reactions were completed at
room temperature within 10–15 min. A wide range of structurally varied
aryl-substituted b-nitroethylene underwent the cyclization reactions by
using this procedure. Several functional groups such as NO2, OMe, Br,

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2H-1,4-Benzothiazin-3(4H)-ketoximes
3539
)
Y
X
R
Y
X
Y
XSmI2
2
SmI2
RCH=CHNO2
THF, r.t.
N
H
NOH
NO2
N(SmI2)2
2
3
X=S, Se
Y=H, Cl
1
MeOH
Y
XH
RCH=CHNO2
NH2
4
Scheme 1.
Table 1. Preparation of 2H-1,4-benzothiazin-3(4H )-ketoximes and 2H-1,4-
benzoselenazin-3(4H )-ketoximes induced by SmI2.
Yield
(%)a
Entry
Y
X
R
Product
T (min)
1
2
H
H
H
H
H
H
H
H
H
H
H
S
C6H5
3a
3b
3c
3d
3e
3f
10
10
10
10
10
10
10
10
15
15
15
83.0b
87
S
4-CH3OC6H4
4-CH3C6H4
3-BrC6H4
3
S
75
68
4
S
5
S
2-NO2C6H4
2,6-Cl2C6H3
2-furanyl
65
71
6
S
7
S
3g
3h
3i
77
8
S
iso-butyl
85
9
Se
Se
Se
4-CH3OC6H4
4-CH3C6H4
iso-butyl
71.0b
72
10
11
3j
3k
82
aIsolated yields based on bis(o-nitrophenyl) disulfides or diselenides.
bMeOH (0.2 mL) was added after the formation of the intermediates 2 and
o-aminothiophenols or o-aminoselenophenols were obtained. In this case, no
products 3 could be detected.
Cl remained unaffected under the present reaction conditions. It should be
noted that alkyl-substituted b-nitroethylenes (entries 8 and 12) were also
effective. However, if the intermediates 2 were protonated by adding
MeOH, the corresponding products
4
(o-aminothiophenols or
o-aminoselenophenols) could be obtained; if b-nitroethylene derivatives
were added at this stage (entries 1 and 9), no products of 3 could be
detected.

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3540
Xu and Zhang
1
The structures of products 3 were confirmed by IR, H NMR, MS
and elemental analysis. The IR spectra of 1–14 exhibited a sharp band
at ꢀ3380 cmꢁ1 (-NH stretching), a broad band at ꢀ3270 cmꢁ1 (¼NOH
stretching) and a medium absorption band at ꢀ1660 cmꢁ1 (C¼N
stretching). The 1H NMR spectra (DMSO-d6 solution) of products
1–14 showed two one-proton singlets at ꢀH ꢀ 10.1 and 9.5 ppm, which
were attributed to the proton of the amine and hydroxy groups,
respectively. The chemical shift of the product in methine groups was
around 5.0 ppm and showed a one-proton singlet. On the other hand,
in the mass spectra of the products 1–14, the molecular ions were the base
peak in most cases (Table 1).
In conclusion, the present procedure provides a novel, efficient, and
general method for the synthesis of 2H-1,4-benzothiazin-3(4H)-
ketoximes and 2H-1,4-benzoselenazin-3(4H)-ketoximes. The advantages
of our method are the easily accessible starting materials, convenient
manipulation and moderate to high yields of the process. Thus this
procedure is endowed with considerable synthetic potential and may
provide a practical method to synthesize the title compounds.
EXPERIMENTAL
Tetrahydrofuran was distilled from sodium-benzophenone immedi-
ately prior to use. All reactions were conducted under a nitrogen
atomsphere. Melting points are uncorrected. 1H NMR spectra were
recorded on a Bruker 400 MHz instrument as CDCl3 or DMSO-d6
solutions using TMS as internal standard. Chemical shifts (ꢀ) are reported
in ppm. Infrared spectra were recorded using KBr disks with a Bruker
Vector-22 infrared spectrometer. Elemental analyses were performed on
a EA-1110 instrument. Metallic samarium and all solvents were purchased
from commercial sources, without further purification before use.
General procedure for the synthesis of 2H-1,4-benzothiazin-3(4H)-
ketoximes and 2H-1,4-benzoselenazin-3(4H)-ketoximes. A solution of
bis(o-nitrophenyl) disulfides or diselenides (0.5 mmol) in dry THF
(5 mL) was added dropwise to the solution of SmI2 (7 mmol) in THF
(45 mL) at room temperature under a nitrogen atmosphere. The deep
blue color of the solution changed to yellow (as for bis(o-nitrophenyl)
disulfides) or brownish red (as for bis(o-nitrophenyl) diselenides) within
5 min. Then a solution of b-nitroethylene derivatives (1.1 mmol) in
anhydrous THF (2 mL) was added. After being stirred for 5–10 min
(Table 1, the reaction was monitored by TLC), the solvent was removed
under reduced pressure. Then water (10 mL) was added and extracted

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2H-1,4-Benzothiazin-3(4H)-ketoximes
3541
with ethyl acetate (3 ꢂ 30 mL). The organic phase was successively
washed with brine (25 mL), water (30 mL) and dried over anhydrous
Na2SO4. The solvent was removed under reduced pressure to give the
crude products, which were purified by preparative TLC using ethyl
acetate and cyclohexane (1:3) as eluant.
Compound 3a. M.p. 164–166ꢃC. ꢁmax: 3380, 3357, 3251, 1666, 1479,
942, 925, 752, 706 cmꢁ1. ꢀH (CDCl3): 7.71–7.42 (2H, brs), 7.38–7.36 (2H,
d), 7.29–7.10 (5H, m), 6.87–6.82 (1H, t), 6.82–6.80 (1H, d), 4.75 (1H, s).
m/z (%): 256 (Mþ, 100), 257 (18.05), 237 (81.29), 77 (22.53), 51 (21.99), 89
(21.26), 109 (19.56). Anal. calcd. C14H12N2OS: C, 65.60; H, 4.72; N,
10.93. Found C, 65.69; H, 4.62; N, 10.88%.
Compound 3b. M.p. 162–164ꢃC. ꢁmax: 3394, 1662, 1609, 1589, 1558,
1248, 754 cmꢁ1. ꢀH (CDCl3): 7.70–7.40 (2H, brs), 7.30–7.08 (4H, m),
6.89–6.79 (3H, m), 4.71 (1H, s), 3.75 (3H, s). m/z (%): 286 (Mþ, 100),
267 (18.94), 253 (26.47), 121 (24.45), 51 (29.02), 77 (27.34), 63 (23.51), 65
(22.47), 45 (20.67). Anal. calcd. C15H14N2O2S: C, 62.92; H, 4.93; N, 9.78.
Found C, 62.88; H, 4.79; N, 9.82%.
Compound 3c. M.p. 148–150ꢃC. ꢁmax: 3363, 3185, 2919, 1647, 1481,
754 cmꢁ1. ꢀH (CDCl3): 7.71–7.39 (2H, brs), 7.26–7.18 (3H, m), 7.10–7.06
(3H, m), 6.88–6.79 (2H, m), 4.72 (1H, s), 2.28 (3H, s). m/z (%): 270 (Mþ,
100.00), 251 (37.45), 237 (36.19), 91 (23.09), 77 (28.03), 65 (22.88), 63
(21.02), 51 (19.78). Anal. calcd. C15H14N2OS: C, 66.64; H, 5.22; N, 10.36.
Found C, 66.54; H, 5.20; N, 10.27%.
Compound 3d. M.p. 115–117ꢃC. ꢁmax: 3398, 3269, 3025, 1653, 1588,
1481 cmꢁ1. ꢀH(DMSO-d6): 10.11 (1H, s), 9.46 (1H, s), 7.47 (1H, s),
7.40–7.38 (1H, d), 7.28–7.20 (3H, m), 7.12–7.05 (2H, m), 6.79–6.75
(1H, t), 5.03 (1H, s). m/z (%): 334 (Mþ, 98.38), 336 (Mþþ2, 100), 317
(57.11), 237 (74.20), 161 (38.50), 135 (41.32). Anal. calcd. C11H13NOS: C,
63.74; H, 6.32; N, 6.76. Found C, 63.89; H, 6.11; N, 6.53%.
Compound 3e. M.p. 131–133ꢃC. ꢁmax: 3375, 1646, 1608, 1589, 1558,
1345, 722 cmꢁ1. ꢀH (DMSO-d6): 10.21 (1H, s), 9.68 (1H, s), 8.02-8.00 (1H,
d), 7.60–7.57 (1H, t), 7.50–7.47 (1H, t), 7.33–7.31 (1H, d), 7.18–7.16 (1H,
d), 7.13–7.09 (1H, t), 7.04–7.02 (1H, d), 6.78–6.74 (1H, t), 5.42 (1H, s).
m/z(%): 301 (Mþ, 22.42), 284 (17.80), 238 (47.77), 220 (40.19), 205
(100), 167 (49.93), 150 (51.78), 77 (43.87). Anal. calcd. C14H11N3O3S:
C, 55.80; H, 3.68; N, 13.95. Found C, 55.87; H, 3.58; N, 13.98%.
Compound 3f. M.p. 184–185ꢃC. ꢁmax: 3294, 1662, 1581, 1560, 1496,
1437, 1375, 727 cmꢁ1. ꢀH (DMSO-d6): 10.24 (1H, s), 9.30 (1H, s),
7.49–7.31 (4H, m), 7.20–7.12 (2H, m), 6.87–6.83 (1H, t), 5.57 (1H, s).
m/z (%): 301 (Mþ, 86.85), 325 (15.28), 326 (56.90), 289 (58.64), 271 (100),
237 (56.27), 136 (89.17), 109 (61.11). Anal. calcd. C14H10Cl2N2OS: C,
51.70; H, 3.10; N, 8.61. Found C, 51.62; H, 3.14; N, 8.82%.

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3542
Xu and Zhang
Compound 3g. M.p. 91–93ꢃC. ꢁmax: 3379, 1647, 1589, 1482, 1375,
749 cmꢁ1. ꢀH (DMSO-d6): 10.04 (1H, s), 9.36 (1H, s), 7.51–7.50 (1H, t),
7.24–7.22 (1H, d), 7.10–7.05 (2H, m), 6.79–6.76 (1H, t), 6.26–5.93 (2H,
m), 503 (1H, s). m/z (%): 246 (Mþ, 100.00), 229 (27.91), 199 (13.52), 186
(22.96), 77 (11.78). Anal. calcd. C12H10N2O2S: C, 58.52; H, 4.09; N,
11.37. Found calcd. C, 58.43; H, 4.11; N, 11.22%.
Compound 3h. Viscous oil. ꢁmax: 3385, 2956, 2868, 1648, 1482, 1387,
931, 748 cmꢁ1. ꢀH (CDCl3): 7.70 (1H, brs), 7.20–7.18 (1H, d), 7.12–7.08
(1H, t), 6.98 (1H, s), 6.90–6.87 (1H, t), 6.80–6.78 (1H, d), 3.58–3.54 (1H,
t), 1.81–1.42 (3H, m), 0.98–0.85 (6H, m). m/z (%): 236 (Mþ, 19.00), 205
(29.82), 180 (58.40), 163 (100.00), 162 (27.33), 136 (38.59), 41 (93.74), 43
(41.72), 57 (30.14). Anal. calcd. C12H16N2OS: C, 60.98, H, 6.82; N, 11.85.
Found C, 60.94; H, 6.79; N, 11.88%.
Compound 3i. M.p. 123–125ꢃC. ꢁmax: 3384, 3275, 2835, 1644, 1608,
1510, 1248 cmꢁ1. ꢀH(DMSO-d6): 10.00 (1H, s, NH), 9.17 (1H, s, OH),
7.28–7.26 (1H, d), 7.19–7.15 (3H, m), 7.10–7.06 (1H, t), 6.77–6.71 (3H,
m), 4.99 (1H, s), 3.66 (3H, s). m/z (%): 334 (80Se-Mþ, 100), 332 (78Se-Mþ,
42.09), 317 (80.89), 286 (46.51), 205 (72.95). Anal. calcd. C15H14N2O2Se:
C, 54.06; H, 4.23; N, 8.41. Found C, 54.11; H, 4.31; N, 8.55%.
Compound 3j. M.p. 118–119ꢃC. ꢁmax: 3424, 1631, 1585, 1511, 1478,
749 cmꢁ1. ꢀH (DMSO-d6): 10.05 (1H, s), 9.18 (1H, s), 7.27–6.99 (7H, m),
6.75–6.72 (1H, t), 4.99 (1H, s), 2.19 (3H, s). m/z (%): 318 (80Se-Mþ,
20.71), 318 (78Se-Mþ, 13.88), 302 (27.14), 285 (19.90), 273 (69.49), 119
(96.33), 91 (100). Anal. calcd. C15H14N2OSe: C, 56.79; H, 4.45; N, 8.83.
Found C, 56.82; H, 4.53; N, 8.92%.
Compound 3k. Viscous oil. ꢁmax: 3397, 2955, 2867, 1646, 1506, 1387,
748 cmꢁ1. ꢀH (CDCl3): 7.63 (1H, s), 7.32–7.30 (1H, d), 7.16–7.12 (1H, t),
6.98 (1H, s), 6.89–6.86 (1H, t), 6.82–6.80 (1H, d), 3.65–3.61 (1H, m),
1.78–1.58 (3H, m), 0.93–0.86 (6H, m). m/z (%): 284 (80Se-Mþ, 7.36),
282 (78Se-Mþ, 3.90), 267 (2.65), 228 (17.69), 220 (25.28), 205 (100.00),
177 (13.65) 91 (21.84), 77 (16.67). Anal. calcd. C12H16N2OSe: C, 50.89;
H, 5.69; N, 9.89. Found C, 50.79; H, 5.65; N, 9.92%.
ACKNOWLEDGMENT
We are grateful to the National Natural Science Foundation of
China (Project No. 20072033) and the NSF of Zhejiang province for
financial support.

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2H-1,4-Benzothiazin-3(4H)-ketoximes
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Received in Japan March 1, 2003

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