One-pot synthesis of 1,4-dihydro-2-thioxo-2H-3,1-benzoxazine-4-acetic acid derivatives by the reaction of 2-isothiocyanatophenyl ketones with lithium enolates of acetates and tertiary acetamides

Article abstract of DOI:10.1002/hlca.201200096

The one-pot synthesis of 4-aryl-1,4-dihydro-2-thioxo-2H-3,1-benzoxazine-4- acetic acid derivatives 2 was achieved in good yields by the reaction of aryl(2-isothiocyanatophenyl)methanones 1 with lithium enolates of acetates and tertiary acetamides. (2E)-1-

Full text of DOI:10.1002/hlca.201200096

Helvetica Chimica Acta – Vol. 95 (2012)
1561
One-Pot Synthesis of 1,4-Dihydro-2-thioxo-2H-3,1-benzoxazine-4-acetic Acid
Derivatives by the Reaction of 2-Isothiocyanatophenyl Ketones with Lithium
Enolates of Acetates and Tertiary Acetamides
by Kazuhiro Kobayashi*, Shuhei Fukamachi, Akihiro Kobayashi, and Aogu Gotoh
Division of Applied Chemistry, Department of Chemistry and Biotechnology, Graduate School of
Engineering, Tottori University, 4-101 Koyama-minami, Tottori 680-8552, Japan
(phone/fax: þ 81-857-315263; e-mail: kkoba@chem.tottori-u.ac.jp)
The one-pot synthesis of 4-aryl-1,4-dihydro-2-thioxo-2H-3,1-benzoxazine-4-acetic acid derivatives 2
was achieved in good yields by the reaction of aryl(2-isothiocyanatophenyl)methanones 1 with lithium
enolates of acetates and tertiary acetamides. (2E)-1-(2-Isothiocyanatophenyl)-3-phenylprop-2-en-1-one
(3) gave 1,4-dihydro-4-[(1E)-2-phenylethenyl]-2-thioxo-2H-3,1-benzoxazine-4-acetic acid derivatives 4
in good yields as well.
Introduction. – The 1,4-dihydro-2H-3,1-benzoxazine-2-thione derivatives are
important compounds, because some of them exhibit biological activities [1]. A
perusal of the literature indicates that this class of heterocycles has been synthesized by
the treatment of the respective 1,4-dihydro-2H-3,1-benzoxazin-2-one derivatives with
Lawesson reagent [1a,b,d]. However, this reaction requires rather high temperatures.
So, we have recently demonstrated the preparation of 4-substituted and 4,4-
disubstituted 1,4-dihydro-2H-3,1-benzoxazine-2-thiones by the reaction of 2-lithio-
phenyl isothiocyanates with aldehydes or ketones [2a], and the preparation of 4-
substituted 4-(alkyloxy)-1,4-dihydro-2H-3,1-benzoxazine-2-thiones by the reaction of
2-isothiocyanatobenzoates with organolithiums [2b], and we decided to develop a
method for the preparation of another type of 1,4-dihydro-2H-3,1-benzoxazine-2-
thione derivatives by investigating reactions of aryl(2-isothiocyanatophenyl)metha-
nones 1 with organometals. Thus we found that lithium enolates of acetates and tertiary
acetamides reacted with 1 cleanly to afford 4-aryl-1,4-dihydro-2-thioxo-2H-3,1-
benzoxazine-4-acetic acid derivatives 2. We also found that 1,4-dihydro-4-[(1E)-2-
phenylethenyl]-2-thioxo-2H-3,1-benzoxazine-4-acetic acid derivatives 4 could be
obtained similarly from (2E)-1-(2-isothiocyanatophenyl)-3-phenylprop-2-en-1-one
(3). In this article, we report the results of our investigation, which provide a
convenient method for the preparation of these new types of 1,4-dihydro-2H-3,1-
benzoxazine-2-thione derivatives.
Results and Discussion. – The one-pot synthesis of 2 from 1, readily prepared from
(2-aminophenyl)phenylmethanones according to the sequence described previously
[3], was conducted as shown in Scheme 1. Thus, acetates and tertiary acetamides 1 were
treated with lithium diisopropylamide (LDA) in THF at ꢀ 788 to generate the
ꢀ 2012 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Helvetica Chimica Acta – Vol. 95 (2012)
corresponding lithium enolates, which were then allowed to react with the 2-
isothiocyanatophenyl ketones 1. The selective attack of the lithium enolates on the
C¼O C-atom of 1 followed by the addition of the alkoxide moiety of the resulting
intermediate A to the isothiocyanato C-atom proceeded smoothly. The progress of the
reaction was monitored by TLC (SiO2) for the disappearance of the starting 2-ketone 1,
and the reactions were complete within 10 min. After usual aqueous workup and
subsequent purification by column chromatography (silica gel), the desired products 2
were generally obtained in good yields (see Table), independently of the substituents at
the benzene ring of 1. Unfortunately, however, when the isothiocyanatophenyl ketones
1 were subjected to reactions with organolithiums such as butyllithium or phenyl-
lithium, considerably complex mixtures of products were formed, from which no more
than trace amounts of the desired products were isolated. It should be noted that the
use of Grignard reagents gave similar results.
Scheme 1
Table. Preparation of 4-Aryl-2-thioxo-2H-1,4-dihydro-3,1-benzoxazine-4-acetic Acid Derivatives 2
1
Y
2
Yielda) [%]
1a (R ¼ H, Ar¼ Ph)
EtO
2a
2b
2c
2d
2e
2f
2g
2h
2i
69
78
78
74
77
78
87
73
77
75
1a
tBuO
1a
1a
1a
Me2N
piperidin-1-yl
morpholin-4-yl
EtO
morpholin-4-yl
tBuO
1b (R ¼ Cl, Ar¼ Ph)
1b
1c (R ¼ H, Ar¼ 4-ClꢀC6H4)
1c
Me2N
tBuO
1d (R ¼ H, Ar¼ 4-MeOꢀC6H4)
2j
a) Yields of isolated products.
Subsequently, we were interested in the reactivity of (2E)-1-(2-isothiocyanato-
phenyl)-3-phenylprop-2-en-1-one (3) with lithium enolates. We found that when 3 was
treated with lithium enolates under the same conditions as described for the
preparation of 2, the addition occurred selectively in the 1,2-addition fashion and
not in a 1,4-addition fashion, to afford 1,4-dihydro-4-[(1E)-1-phenylethenyl]-2-thioxo-
2H-3,1-benzoxazine-4-acetic acid derivatives 4 as illustrated in Scheme 2. The yields of
4 were comparable to those of 2.

Helvetica Chimica Acta – Vol. 95 (2012)
1563
Scheme 2
In summary, an efficient method for preparing 1,4-dihydro-2H-3,1-benzoxazine-2-
thione derivatives 2 and 4 by the reaction of aryl(2-isothiocyanatophenyl)methanones 1
and (2E)-1-(2-isothiocyanatophenyl)-3-phenylprop-2-en-1-one (3), respectively, with
lithium enolates of acetates and tertiary acetamides was developed. The present
method may be of value because of the ready availability of the starting materials and
the simplicity of the operations.
This work was supported in part by a Grant-in-Aid for Scientific Research (C) 22550035 from Japan
Society for the Promotion of Science. We thank Mrs. Miyuki Tanmatsu of this university for recording
mass spectra and performing combustion analyses.
Experimental Part
1. General. Aryl(2-isothiocyanatophenyl)methanones 1 were prepared according to the reported
procedure [3]. BuLi was supplied by Asia Lithium Corporation. All other chemicals used in this study
were commercially available. All of the org. solvents used were dried over the appropriate drying agents
and distilled under Ar prior to use. TLC: Merck silica gel 60 PF254. Column chromatography (CC): Wako
Gel C-200E. M.p.: Laboratory-Devices-Mel-Temp-II melting-point apparatus; uncorrected. IR Spectra:
1
Shimadzu-FTIR-8300 spectrometer; ˜n in cmꢀ1. H-NMR Spectra (500 or 400 MHz): Jeol-ECP-500 FT
NMR spectrometer or Jeol-LA400 FT NMR spectrometer; d in ppm rel. to Me4Si as internal standard, J
in Hz. 13C-NMR (125 MHz): Jeol-ECP-500 FT NMR spectrometer; d in ppm rel. to Me4Si as internal
standard. MS (EI, 70 eV): Jeol-JMS-AX-505-HA spectrometer; in m/z (rel. %).
2. (2E)-1-(2-Isothiocyanatophenyl)-3-phenylprop-2-en-1-one (3). Compound 3 was prepared start-
ing with (2E)-1-(2-aminophenyl)-3-phenylprop-2-en-1-one [4], via N-{2-[(2E)-1-oxo-3-phenylprop-2-en-
1-yl]phenyl}formamide and (2E)-1-(2-isocyanophenyl)-3-phenylprop-2-en-1-one, followed by the se-
quence reported previously for the preparation of 1 [3].
N-{2-[(2E)-1-Oxo-3-phenylprop-2-en-1-yl)phenyl}formamide: Yield 74%. Yellow crystals. M.p.
132 – 1358 (toluene). IR (KBr): 3179, 1690, 1634. 1H-NMR (400 MHz): 7.22 (t, J ¼ 7.3, 1 H); 7.45 – 7.65 (m,
8 H); 7.82 (d, J ¼ 15.6, 1 H); 7.80 (d, J ¼ 7.3, 1 H); 8.52 – 11.43 (m, 2 H). Anal. calc. for C16H13NO2
(251.28): C 76.48, H 5.21, N 5.57; found: C 76.50, H 5.25, N 5.55.
(2E)-1-(2-Isocyanophenyl)-3-phenylprop-2-en-1-one: Yield 70%. Yellow solid. M.p. 818 (hexane/
Et2O, dec.). IR (KBr): 2124, 1645, 1601: 1H-NMR (500 MHz): 7.26 (d, J ¼ 16.0, 1 H); 7.40 – 7.45 (m, 3 H);
7.50 – 7.57 (m, 3 H); 7.58 – 7.64 (m, 3 H); 7.68 (dd, J ¼ 7.3, 1.4, 1 H). Anal. calc. for C16H11NO (233.26): C
82.38, H 4.75, N 6.00; found: C 82.31, H 4.76, N 5.75.
Compound 3: Yield 69%. Orange solid. M.p. 85 – 878 (hexane/Et2O). IR (KBr): 2106, 1667, 1645,
1
1604. H-NMR (500 MHz): 7.27 (d, J ¼ 13.3, 1 H); 7.36 – 7.44 (m, 5 H); 7.52 (td, J ¼ 7.8, 1.4, 1 H); 7.62 –
7.68 (m, 4 H). Anal. calc. for C16H11NOS (265.33): C 72.43, H 4.18, N 5.28; found: C 72.40, H 4.20, N 5.18.
3. One-Pot Synthesis: General Procedure, Ethyl 1,4-Dihydro-4-phenyl-2-thioxo-2H-3,1-benzoxazine-
4-acetate (2a). To a stirred soln. of LDA (0.97 mmol), generated from BuLi and (iPr)2NH by the standard
method, in THF (2 ml) at ꢀ 788 was added dropwise AcOEt (85 mg, 0.97 mmol). After 15 min, 1a

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Helvetica Chimica Acta – Vol. 95 (2012)
(0.20 g, 0.97 mmol) in THF (2 ml) was added dropwise, and stirring was continued for an additional
10 min at ꢀ 788. Sat. aq. NH4Cl (10 ml) was added and the mixture was extracted with AcOEt (3 ꢁ
10 ml). The combined extract was washed with brine, dried (Na2SO4), and concentrated, and the
residue purified by CC (SiO2): 2a (0.22 g, 69%). Pale yellow amorphous powder. Rf (AcOEt/hexane 1:5)
0.16. IR (neat): 3219 1730, 1620, 1601. 1H-NMR (500 MHz, CDCl3): 1.09 (t, J ¼ 7.4, 3 H); 3.40 (d, J ¼ 16.0,
1 H); 3.48 (d, J ¼ 16.0, 1 H); 4.00 – 4.08 (m, 2 H); 6.91 (d, J ¼ 8.0, 1 H); 7.30 (t, J ¼ 7.4, 1 H); 7.23 – 7.50 (m,
7 H); 10.07 (br. s, 1 H). 13C-NMR (CDCl3): 13.91; 45.04; 60.94; 86.67; 114.31; 122.90; 124.79; 125.51;
125.73; 128.64; 128.80; 129.61; 132.20; 140.83; 167.98; 183.35. MS: 327 (37, Mþ), 240 (100). Anal. calc. for
C18H17NO3S (327.40): C 66.03, H 5.23, N 4.28; found: C 55.84, H 5.19, N 4.44.
1,1-Dimethylethyl 1,4-Dihydro-4-phenyl-2-thioxo-2H-3,1-benzoxazine-4-acetate (2b): White solid.
1
M.p. 143 – 1458 (hexane/Et2O). IR (KBr): 3181, 1727, 1620, 1157. H-NMR (400 MHz, CDCl3): 1.26 (s,
9 H); 3.32 (d, J ¼ 16.6, 1 H); 3.43 (d, J ¼ 16.6, 1 H); 6.83 (d, J ¼ 7.3, 1 H); 7.23 (dd, J ¼ 7.8, 7.3, 1 H); 7.28 –
7.36 (m, 6 H); 7.40 (d, J ¼ 7.8, 1 H); 9.13 (br. s, 1 H). 13C-NMR (CDCl3): 27.70; 46.61; 81.55; 86.90; 114.25;
122.99; 124.77; 125.55; 125.70; 128.60; 128.69; 129.51; 132.06; 140.95; 167.22; 183.26. MS: 355 (41, Mþ),
240 (100). Anal. calc. for C20H21NO3S (355.45): C 67.58, H 5.95, N 3.94; found: C 67.56, H 6.02, N 3.74.
1,4-Dihydro-N,N-dimethyl-4-phenyl-2-thioxo-2H-3,1-benzoxazine-4-acetamide (2c): Pale yellow sol-
id. M.p. 229 – 2318 (THF). IR (KBr): 3173, 1630, 1174. 1H-NMR (500 MHz, (D6)DMSO): 2.72 (s, 3 H);
2.99 (s, 3 H); 3.36 (d, J ¼ 17.2, 1 H); 3.71 (d, J ¼ 17.2, 1 H); 6.96 (d, J ¼ 8.0, 1 H); 7.13 (t, J ¼ 7.4, 1 H);
7.24 – 7.36 (m, 6 H); 7.49 (d, J ¼ 7.4, 1 H); 12.02 (br. s, 1 H). 13C-NMR ((D6)DMSO): 34.85; 36.86; 42.11;
86.25; 114.02; 123.95; 124.14; 125.40; 128.06; 128.39; 128.44; 132.08; 142.97; 166.89; 182.19. MS: 326 (100,
Mþ). Anal. calc. for C18H18N2O2S (326.41): C 66.23, H 5.56, N 8.58; found: C 66.22, H 5.48, N 8.40.
(1,4-Dihydro-4-phenyl-2-thioxo-2H-3,1-benzoxazin-4-yl)methyl](piperidin-1-yl)methanone (2d):
1
White solid. M.p. 209 – 2138 (hexane/THF). IR (KBr): 3185, 1612, 1169. H-NMR (500 MHz, CDCl3):
1.47 – 1.71 (m, 6 H); 3.43 (d, J ¼ 15.5, 1 H); 3.46 – 3.62 (m, 5 H); 6.73 (d, J ¼ 7.4, 1 H); 7.13 (dd, J ¼ 8.0, 7.4,
1 H); 7.20 (t, J ¼ 7.4, 1 H); 7.23 – 7.31 (m, 5 H); 7.66 (d, J ¼ 8.0, 1 H); 9.84 (br. s, 1 H). 13C-NMR (CDCl3):
24.37; 25.49; 26.49; 42.92; 43.08; 47.77; 88.00; 114.23; 123.07; 124.52; 125.55; 126.47; 128.45; 128.50;
129.25; 132.21; 141.70; 165.62; 183.19. MS: 366 (100, Mþ). Anal. calc. for C21H22N2O2S (366.48): C 68.82,
H 6.05, N 7.64; found: C 68.74, H 6.05, N 7.59.
[(1,4-Dihydro-4-phenyl-2-thioxo-2H-3,1-benzoxazin-4-yl)methyl](morpholin-4-yl)methanone (2e):
1
White solid. M.p. 233 – 2358 (hexane/THF). IR (KBr): 3183, 1626, 1165. H-NMR (400 MHz, CDCl3):
3.37 – 3.84 (m, 10 H); 6.75 (d, J ¼ 7.8, 1 H); 7.27 – 7.34 (m, 7 H); 7.73 (d, J ¼ 7.3, 1 H); 8.77 (br. s, 1 H).
13C-NMR (CDCl3): 42.19; 42.86; 47.17; 66.76; 66.89; 88.06; 114.10; 122.69; 124.67; 125.41; 125.96; 126.64;
128.69 (2 C); 129.65; 141.36; 165.85; 183.14. MS: 368 (100, Mþ). Anal. calc. for C20H20N2O3S (368.45): C
65.20, H 5.47, N 7.60; found: C 65.18, H 5.47, N 7.50.
Ethyl 6-Chloro-1,4-dihydro-4-phenyl-2-thioxo-2H-3,1-benzoxazine-4-acetate (2f): Pale yellow solid.
1
M.p. 166 – 1698 (hexane/THF). IR (KBr): 3179, 1742, 1619, 1156. H-NMR (400 MHz, CDCl3): 1.13 (t,
J ¼ 7.4, 3 H); 3.37 (d, J ¼ 16.0, 1 H); 3.46 (d, J ¼ 16.0, 1 H); 4.06 (q, J ¼ 7.4, 2 H); 6.88 (d, J ¼ 8.0, 1 H);
7.29 – 7.35 (m, 7 H); 9.5 – 10.5 (br., 1 H). 13C-NMR (CDCl3): 13.91; 44.83; 61.11; 86.34; 115.67; 124.61;
125.64 (2 C), 128.80; 129.07; 129.67; 130.00; 130.86; 140.11; 167.68; 182.95. MS: 361 (27, Mþ), 274 (100).
Anal. calc. for C18H16ClNO3S (361.84): C 59.75, H 4.46, N 3.87; found: C 59.65, H 4.47, N 3.65.
[(6-Chloro-1,4-dihydro-4-phenyl-2-thioxo-2H-3,1-benzoxazin-4-yl)methyl](morpholin-4-yl)metha-
none (2g): Pale yellow solid. M.p. 151 – 1538 (hexane/THF). IR (KBr): 3187, 1626, 1165. 1H-NMR
(400 MHz, CDCl3): 3.45 – 3.94 (m, 10 H); 6.69 (d, J ¼ 8.0, 1 H); 7.10 (d, J ¼ 8.0, 1 H); 7.26 – 7.32 (m, 5 H);
7.80 (s, 1 H); 10.42 (br. s, 1 H). 13C-NMR (CDCl3): 42.31; 42.74; 47.23; 66.66; 66.80; 87.64; 115.78; 124.39;
125.22; 126.54; 128.86 (2 C); 129.30; 129.68; 131.26; 141.04; 166.17; 182.60. MS: 402 (100, Mþ). Anal. calc.
for C20H19ClN2O3S (402.89): C 59.62, H 4.75, N 6.95; found: C 59.42, H 4.69, N 6.90.
1,1-Dimethylethyl 4-(4-Chlorophenyl)-1,4-dihydro-2-thioxo-2H-3,1-benzoxazine-4-acetate (2h): Pale
yellow solid. M.p. 168 – 1708 (hexane/CH2Cl2). IR (KBr): 3188, 1728, 1620, 1602, 1158. 1H-NMR
(400 MHz, CDCl3): 1.27 (s, 9 H); 3.29 (d, J ¼ 16.1, 1 H); 3.39 (d, J ¼ 16.1, 1 H); 6.83 (d, J ¼ 7.8, 1 H); 7.22 –
7.40 (m, 7 H); 8.98 (br. s, 1 H). 13C-NMR (CDCl3): 27.73; 46.42; 81.76; 86.32; 114.35; 122.74; 124.92;
125.48; 127.32; 128.79; 129.78; 132.11; 134.80; 139.43; 166.96; 183.10. MS: 389 (60, Mþ), 274 (100). Anal.
calc. for C20H20ClNO3S (389.90): C 61.61, H 5.17, N 3.59; found: C 61.42, H 5.17, N 3.69.

Helvetica Chimica Acta – Vol. 95 (2012)
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4-(4-Chlorophenyl)-1,4-dihydro-N,N-dimethyl-2-thioxo-2H-3,1-benzoxazine-4-acetamide (2i): Pale
yellow amorphous powder. Rf (THF/hexane 1:1) 0.41. IR (KBr): 3181, 1623, 1172. 1H-NMR (400 MHz,
CDCl3): 2.89 (s, 3 H); 3.13 (s, 3 H); 3.40 (d, J ¼ 15.6, 1 H); 3.50 (d, J ¼ 15.6, 1 H); 6.77 (d, J ¼ 7.8, 1 H);
7.21 – 7.34 (m, 6 H); 7.57 (d, J ¼ 7.8, 1 H); 9.03 (br. s, 1 H). 13C-NMR (CDCl3): 35.77; 38.23; 43.15; 87.41;
114.23; 122.95; 124.78; 126.30; 127.31; 128.71; 129.57; 132.19; 134.66; 139.98; 167.05; 182.99. MS: 360 (100,
Mþ). Anal. calc. for C18H17ClN2O2S (360.86): C 59.91, H 4.75, N 7.76; found: C 59.83, H 4.80, N 7.54.
1,1-Dimethylethyl 1,4-Dihydro-4-(4-methoxyphenyl)-2-thioxo-2H-3,1-benzoxazine-4-acetate (2j):
1
White solid. M.p. 163 – 1648 (hexane/CH2Cl2). IR (KBr): 3182, 1719, 1620, 1171. H-NMR (500 MHz,
CDCl3): 1.26 (s, 9 H); 3.29 (d, J ¼ 16.0, 1 H); 3.43 (d, J ¼ 16.0, 1 H); 3.77 (s, 3 H); 6.83 (d, J ¼ 8.6, 3 H);
7.20 (d, J ¼ 8.6, 2 H); 7.21 (dd, J ¼ 8.0, 7.4, 1 H); 7.33 (dd, J ¼ 8.0, 7.4, 1 H); 7.36 (d, J ¼ 8.0, 1 H); 9.11 (s,
1 H). 13C-NMR (CDCl3): 27.73; 46.68; 55.24; 81.48; 86.84; 113.87; 114.20; 123.20; 124.68; 125.56; 127.25;
129.42; 132.15; 133.09; 159.71; 167.33; 183.30. MS: 385 (82, Mþ), 270 (100). Anal. calc. for C21H23NO4S
(385.48): C 65.43, H 6.01, N 3.63; found: C 65.19, H 6.03, N 3.88.
Ethyl 1,4-Dihydro-4-[(1E)-2-phenylethenyl]-2-thioxo-2H-3,1-benzoxazine-4-acetate (4a): Yield
1
64%. Pale yellow solid. M.p. 143 – 1468 (hexane/CH2Cl2). IR (KBr): 3201, 1749, 1625, 1168. H-NMR
(400 MHz, CDCl3): 1.15 (t, J ¼ 7.3, 3 H); 3.26 (d, J ¼ 16.1, 1 H); 3.32 (d, J ¼ 16.1, 1 H); 4.05 – 4.10 (m,
2 H); 6.40 (d, J ¼ 16.1, 1 H); 6.46 (d, J ¼ 16.1, 1 H); 6.85 (d, J ¼ 7.8, 1 H); 7.17 – 7.34 (m, 8 H); 9.07 (br. s,
1 H). 13C-NMR (CDCl3): 13.98; 44.05; 61.01; 85.45; 114.25; 121.90; 124.88; 125.08; 127.01; 128.41; 128.61
(2 C); 129.59; 131.86; 132.61; 135.16; 168.01; 182.87. MS: 353 (67, Mþ), 266 (100). Anal. calc. for
C20H19NO3S (353.43): C 67.97, H 5.42, N 3.96; found: C 67.68, H 5.47, N 4.07.
1,1-Dimethylethyl 2-{1,4-Dihydro-4-[(1E)-2-phenylethenyl]-2-thioxo-2H-3,1-benzoxazine-4-acetate
(4b): Yield 76%. White solid. M.p. 165 – 1678 (hexane/CH2Cl2). IR (KBr): 3187, 1727, 1624, 1602,
1
1172. H-NMR (400 MHz, CDCl3): 1.29 (s, 9 H); 3.18 (d, J ¼ 16.1, 1 H); 3.27 (d, J ¼ 16.1, 1 H); 6.37 (d,
J ¼ 16.1, 1 H); 6.43 (d, J ¼ 16.1, 1 H); 6.88 (d, J ¼ 7.8, 1 H); 7.17 – 7.32 (m, 8 H); 9.44 (br. s, 1 H). 13C-NMR
(CDCl3): 27.74; 45.61; 81.70; 85.76; 114.23; 121.89; 124.86; 125.05; 126.95; 128.51; 128.56; 128.72; 129.44;
131.74; 132.26; 135.13; 167.25; 182.74. Anal. calc. for C22H23NO3S (381.49): C 69.26, H 6.08, N 3.67; found;
C 69.00, H 6.06, N 3.69.
1,4-Dihydro-N,N-dimethyl-4-[(1E)-2-phenylethenyl]-2-thioxo-2H-3,1-benzoxazine-4-acetamide
(4c): Yield 77%. Pale yellow solid. M.p. 175 – 1788 (hexane/CH2Cl2). IR (KBr): 3182, 1624, 1175.
1H-NMR (400 MHz, CDCl3): 2.91 (s, 3 H); 3.09 (s, 3 H); 3.25 (d, J ¼ 15.6, 1 H); 3.40 (d, J ¼ 15.6, 1 H);
6.46 (d, J ¼ 16.6, 1 H); 6.54 (d, J ¼ 16.6, 1 H); 6.80 (d, J ¼ 7.8, 1 H); 7.16 – 7.39 (m, 8 H); 9.04 (br. s, 1 H).
13C-NMR (CDCl3): 35.75; 38.14; 42.46; 86.57; 114.12; 122.37; 124.96; 125.58; 126.99; 128.36; 128.53;
129.10; 129.27; 131.73; 131.78; 135.43; 157.41; 182.77. MS: 352 (100, Mþ). Anal. calc. for C20H20N2O2S
(352.45): C 68.16, H 5.72, N 7.95; found: C 68.05, H 5.79, N 7.88.
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Received February 28, 2012