Use of Molecular Oxygen as a Reoxidant in the Synthesis of 2-Substituted Benzothiazoles
7.75 (2H, d, J=8.0 Hz), 7.92 (1H, d, J=8.0 Hz), 8.09 (1H,
d, J=8.0 Hz), 8.17 (2H, d, J=8.0 Hz); 13C NMR (100 MHz,
CDCl3): d=114.1, 118.2, 121.8, 123.8, 126.0, 126.8, 127.9,
132.7, 135.3, 137.4, 154.0, 165.3; MS: m/z (relative intensity
%)=236 (M+, 100); HR-MS: m/z=236.0409, calcd. for
C14H8N2S: 236.0408.
2-(4-Chlorophenyl)benzothiazole (2n): mp 111.5–112.58C
(colorless prisms from hexane:AcOEt, lit.[37] mp 118–
1208C); 1H NMR (400 MHz, CDCl3): d=7.39 (1H, t, J=
7.8 Hz), 7.46 (2H, d, J=8.6 Hz), 7.49 (1H, t, J=7.8 Hz),
7.89 (1H, d, J=7.8 Hz), 8.02 (2H, d, J=8.6 Hz), 8.06 (1H,
d, J=7.8 Hz); 13C NMR (100 MHz, CDCl3): d=121.6, 123.2,
125.3, 126.4, 128.6, 129.2, 132.0, 135.0, 136.9, 154.0, 166.5;
MS: m/z (relative intensity %)=247 (M+ +2, 42), 245 (M+,
100); HR-MS: m/z=245.0049, calcd. for C13H835ClNS:
245.0066.
Representative Procedure for Preparation of
Thioureas (4a–i): N-Benzyl-N’-phenylthiourea (4a)
Phenyl isothiocyanate (2.0 g, 15.0 mmol) was added to a so-
lution of benzylamine (1.7 g, 15.8 mmol) in MeCN (20 mL)
at room temperature and the mixture was stirred for 1 h at
the same temperature. MeCN was removed under reduced
pressure and the precipitate was washed with Et2O (5 mLꢁ
3) and hexane (5 mLꢁ3). Recrystallization from hexane-
acetone gave 4a as colorless prisms; yield: 2.5 g (85%); mp
153–1548C (lit.[39] mp 151.2–151.78C); IR (film): n=1537,
1
1352, 1244 cmÀ1; H NMR (400 MHz, CDCl3): d=4.87 (2H,
d, J=5.2 Hz), 6.28 (1H, br.s), 7.21 (2H, d, J=8.0 Hz), 7.25–
7.34 (6H, m), 7.39 (2H, t, J=7.2 Hz), 8.06 (1H, br.s);
13C NMR (100 MHz, CDCl3): d=49.5, 125.2, 127.3, 127.5,
127.6, 128.7, 130.2, 135.8, 137.1, 180.7; MS: m/z (relative in-
tensity %)=242 (M+, 48), 91 (100); HR-MS: m/z=
242.0875, calcd. for C14H14N2S: 242.0878.
2-(4-Methoxyphenyl)benzothiazole (2o): mp 119–1208C
(colorless prisms from hexane:AcOEt, lit.[32] mp 121–
N-(4-Methoxybenzyl)-N’-phenylthiourea (4b): obtained as
1
1228C); H NMR (400 MHz, CDCl3): d=3.87 (3H, s), 6.99
colorless needles; yield: 86%; mp 109–1108C (lit.[40] mp
(2H, d, J=8.4 Hz), 7.34 (1H, t, J=7.6 Hz), 7.46 (1H, t, J=
7.6 Hz), 7.86 (1H, d, J=7.6 Hz), 8.01–8.03 (3H, m);
13C NMR (100 MHz, CDCl3): d=55.5, 114.3, 121.4, 122.7,
124.7, 126.1, 126.4, 129.0, 134.8, 154.1, 161.8, 167.7; MS: m/z
(relative intensity %)=241 (M+, 100); HR-MS: m/z=
241.0555, calcd. for C14H11NOS: 241.0561.
2-(3-Methoxyphenyl)benzothiazole (2p): mp 81.5–828C
(pale orange plates from hexane:AcOEt, lit.[32] mp 81–
828C); 1H NMR (400 MHz, CDCl3): d=3.90 (3H, s), 7.03
(1H, dd, J=8.3, 2.6 Hz), 7.35–7.40 (2H, m), 7.48 (1H, t, J=
7.5 Hz), 7.62–7.67 (2H, m), 7.88 (1H, d, J=7.5 Hz), 8.07
(1H, d, J=8.3 Hz); 13C NMR (100 MHz, CDCl3): d=55.5,
112.0, 117.2, 120.1, 121.5, 123.2, 125.1, 126.2, 129.9, 134.8,
135.0, 153.9, 159.9, 167.8; MS: m/z (relative intensity %) 241
(M+, 100); HR-MS: m/z=241.0532, calcd. for C14H11NOS:
241.0561.
1078C); IR (film): n=3209, 1512, 1247, 1175, 1031 cmÀ1
;
1H NMR (400 MHz, CDCl3): d=3.77 (3H, s), 4.78 (2H, d,
J=5.2 Hz), 6.25 (1H, br.s), 6.83 (2H, d, J=8.4 Hz), 7.18–
7.30 (5H, m), 7.37 (2H, t, J=7.8 Hz), 8.26 (1H, br.s);
13C NMR (100 MHz, CDCl3): d=48.9, 55.2, 114.0, 125.0,
127.1, 128.9, 129.1, 130.0, 135.9, 159.0, 180.3; MS: m/z (rela-
tive intensity %)=272 (M+, 28), 121 (100); HR-MS: m/z=
272.0996, calcd. for C15H16N2OS: 272.0983.
N-(4-Nitrobenzyl)-N’-phenylthiourea (4c): obtained as
pale yellow prisms; yield: 87%; mp 163–1648C; IR (film):
n=3200, 1516, 1343, 1185 cmÀ1 1H NMR (400 MHz, ace-
;
tone-d6): d=5.04 (2H, d, J=6.0 Hz), 7.19 (1H, t, J=
7.7 Hz), 7.36 (2H, t, J=7.7 Hz), 7.42–7.45 (2H, m), 7.63
(2H, d, J=8.8 Hz), 7.81 (1H, br.s), 8.18 (2H, d, J=8.8 Hz),
9.08 (1H, br.s); 13C NMR (100 MHz, acetone-d6): d=48.1,
124.1, 125.4, 126.4, 129.1, 130.0, 139.2, 147.8, 148.3, 183.1;
MS: m/z (relative intensity %)=287 (M+, 38), 135 (100);
HR-MS: m/z=287.0711, calcd. for C14H13N3O2S: 287.0729;
anal. calcd. for C14H13N3O2S: C 58.52, H 4.56, N 14.62;
found: C 58.46, H 4.61, N 14.64.
6-Cyano-2-(4-methoxyphenyl)benzothiazole (2q): mp 197–
197.58C (red plates from hexane:AcOEt); IR (film): n=
2224 cmÀ1 1H NMR (400 MHz, CDCl3): d=3.90 (3H, s),
;
7.11 (2H, d, J=8.6 Hz), 7.70 (1H, dd, J=8.4, 1.4 Hz), 8.04
(2H, d, J=8.6 Hz), 8.05 (1H, d, J=8.4 Hz), 8.18 (1H, d, J=
1.4 Hz); 13C NMR (100 MHz, CDCl3): d=55.6, 107.9, 114.6,
118.8, 123.3, 125.4, 126.1, 129.4, 129.5, 135.3, 156.6, 162.7,
166.2; MS: m/z (relative intensity %)=266 (M+, 100); HR-
MS: m/z=266.0516, calcd. for C15H10N2OS: 266.0514.
N-(2-Methylbenzyl)-N’-phenylthiourea (4d): obtained as
colorless prisms; yield: 97%; mp 202–2038C (lit.[41] mp
1898C); IR (film): n=3371, 3153, 1537, 1246, 1173 cmÀ1
;
1H NMR (400 MHz, CDCl3): d=2.31 (3H, s), 4.84 (2H, d,
J=4.8 Hz), 6.04 (1H, br.s), 7.15–7.29 (7H, m), 7.39 (2H, t,
J=7.8 Hz), 7.67 (1H, br.s); 13C NMR (100 MHz, CDCl3):
d=19.1, 47.9, 125.3, 126.2, 127.5, 128.0, 128.4, 130.3, 130.6,
134.8, 135.9, 136.4, 180.8; MS: m/z (relative intensity %)=
256 (M+, 42), 105 (100); HR-MS: m/z=256.1015, calcd. for
C15H16N2S: 256.1034; anal. calcd. for C15H16N2S: C 70.27, H
6.29, N 10.93; found: C 70.32, H 6.30, N 10.88.
2-PhenylthiazoloACHTUNGTRENNUNG[4,5-c]pyridine (2r): mp 147.5–148.58C
(pale orange prisms from hexane:AcOEt, lit.[38] mp 147–
1
1488C); H NMR (400 MHz, DMSO-d6): d=7.58–7.64 (3H,
m), 8.12 (2H, d, J=7.2 Hz), 8.22 (1H, d, J=4.8 Hz), 8.53
(1H, br), 9.32 (1H, br); 13C NMR (100 MHz, DMSO-d6):
d=117.6, 127.7, 129.7, 132.2, 132.4, 142.6, 144.0, 144.7, 150.4,
169.1; MS: m/z (relative intensity %)=212 (M+, 100); HR-
MS: m/z=212.0393, calcd. for C12H8N2S: 212.0408.
N-Benzyl-N’-(4-methoxyphenyl)thiourea (4e): obtained as
colorless needles; yield: 94%; mp 113–1148C (lit.[42] mp 108–
1098C); IR (film): n=3337, 1597, 1508, 1258, 1171 cmÀ1
;
2-PhenylthiazoloACHTUNGTRENNUNG[5,4-c]pyridine (2s): mp 136–136.58C
(colorless prisms from hexane:AcOEt, lit.[38] mp 133–
1H NMR (400 MHz, CDCl3): d=3.78 (3H, s), 4.85 (2H, d,
J=5.6 Hz), 6.08 (1H, br.s), 6.89 (2H, d, J=8.8 Hz), 7.14
(2H, d, J=8.8 Hz), 7.24–7.33 (5H, m), 7.91 (1H, br.s);
13C NMR (100 MHz, CDCl3): d=49.3, 55.5, 115.3, 127.4,
127.5, 127.6, 128.1, 128.6, 137.3, 158.9, 181.3; MS: m/z (rela-
tive intensity %)=272 (M+, 49), 91 (100); HR-MS: m/z=
272.0977, calcd. for C15H16N2OS: 272.0983.
1
1348C); H NMR (400 MHz, CDCl3): d=7.50–7.56 (3H, m),
7.93 (1H, d, J=4.8 Hz), 8.13 (2H, d, J=7.6 Hz), 8.65 (1H,
d, J=4.8 Hz), 9.20 (1H, s); 13C NMR (100 MHz, CDCl3):
d=117.3, 128.0, 129.2, 132.0, 132.1, 132.7, 144.2, 145.9, 158.8,
173.3; MS: m/z (relative intensity %)=212 (M+, 100); HR-
MS: m/z=212.0394, calcd. for C12H8N2S: 212.0408.
Adv. Synth. Catal. 2010, 352, 2643 – 2655
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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