902
X. Fan et al. / Tetrahedron Letters 52 (2011) 899–902
(1 mmol) and FeCl3Á6H2O (0.1 mmol). The reaction mixture was stirred at 80 °C
22. Aotsuka, T.; Abe, N.; Fukushima, K.; Ashizawa, N.; Yoshida, M. Bioorg. Med.
Chem. Lett. 1997, 7, 1677.
for the time period as shown in Table 2. Upon completion, the mixture was
cooled to room temperature and extracted with ethyl ether (5 mL Â 3). The
combined organic phases were concentrated under vacuum. The crude product
was purified by column chromatography eluting with ethyl acetate/hexane (1–
10%) to give the desired product 4. Details of analytical data of selected
compounds are presented as follows: 4a: yellow solid, mp 96–98 °C (lit.4 mp
98–99 °C); 1H NMR (400 MHz, CDCl3) d: 7.55–7.63 (m, 4H, ArH), 7.69 (t, 1H,
J = 7.2 Hz, ArH), 8.04 (d, 1H, J = 7.2 Hz, ArH), 8.27 (d, 1H, J = 7.6 Hz, ArH), 8.58
(d, 2H, J = 7.2 Hz, ArH); 13C NMR (100 MHz, CDCl3) d: 122.16, 125.72, 126.92,
127.61, 128.50, 131.26, 133.90, 134.95, 136.99, 153.87, 167.09, 185.39. MS: m/
z 240 (MH)+. 4b: colorless solid, mp 120–121 °C (lit.4 mp 122–123 °C); 1H NMR
(400 MHz, CDCl3) d: 3.93 (s, 3H, OCH3), 7.05 (d, 2H, J = 8.8 Hz, ArH), 7.52–7.61
(m, 2H, ArH), 8.02 (d, 1H, J = 7.6 Hz, ArH), 8.24 (d, 1H, J = 8.4 Hz, ArH), 8.65 (d,
2H, J = 8.8 Hz, ArH); 13C NMR (100 MHz, CDCl3) d: 55.58, 113.88, 122.14,
125.53, 126.81, 127.39, 127.71, 133.85, 136.85, 153.86, 164.37, 167.87, 183.46.
MS: m/z 270 (MH)+. 4h: pink solid, mp 149–151 °C; 1H NMR (400 MHz, CDCl3)
d: 7.23–7.26 (d, 2H, J = 8.8 Hz, ArH), 7.53 (dd, 1H, J1 = 8.8 Hz, J2 = 2.0 Hz, ArH),
7.94 (d, 1H, J = 8.8 Hz, ArH), 8.23 (d, 1H, J = 1.6 Hz, ArH), 8.64–8.68 (m, 2H,
ArH); 13C NMR (100 MHz, CDCl3) d: 115.73, 115.94, 122.98, 125.19, 128.32,
130.90, 133.07, 134.16, 134.26, 135.17, 154.51,165.22, 168.80, 183.13. MS: m/z
292 (MH)+. HRMS (FAB) calcd for C14H8ClFNOS: 292.0000 [M+H], found:
291.9992. 4j: pale brown solid, mp 110–112 °C (lit.6 mp 106–108 °C); 1H NMR
(400 MHz, CDCl3) d: 7.48 (t, 1H, J = 8.0 Hz, ArH), 7.57–7.71 (m, 4H, ArH), 7.92
(dd, 1H, J1 = 8.0 Hz, J2 = 0.8 Hz, ArH), 8.68 (dd, 2H, J1 = 8.4 Hz, J2 = 1.2 Hz, ArH);
13C NMR (100 MHz, CDCl3) d: 120.63, 127.04, 128.04, 128.55, 130.63, 131.51,
134.12, 134.56, 138.42, 151.00, 167.79, 184.49. MS: m/z 274 (MH)+. 4k:
colorless solid, mp 118–120 °C; 1H NMR (400 MHz, CDCl3) d: 2.48 (s, 3H, CH3),
7.38 (d, 2H, J = 8.0 Hz, ArH), 7.47 (t, 1H, J = 8.0 Hz, ArH), 7.61 (d, 1H, J = 8.0 Hz,
ArH), 7.91 (d, 1H, J = 8.0 Hz, ArH), 8.59 (d, 2H, J = 8.4 Hz, ArH); 13C NMR
(100 MHz, CDCl3) d: 21.87, 120.65, 126.99, 127.95, 129.36, 130.50, 131.66,
131.98, 138.37, 145.35, 151.10, 167.50, 184.08. MS: m/z 288 (MH)+. HRMS
(FAB) calcd for C15H11ClNOS: 288.0251 [M+H], found: 288.0249.
23. Sharpe, C. J.; Palmer, P. J.; Evans, D. E.; Brown, G. R.; King, G.; Shadbolt, R. S.;
Trigg, R. B.; Ward, R. J. J. Med. Chem. 1972, 15, 523.
24. Heynderickx, A.; Guglielmetti, R.; Dubest, R.; Aubard, J.; Samat, A. Synthesis
2003, 1112.
25. (a) Chakraborti, A. K.; Selvam, C.; Kaur, G.; Bhagat, S. Synlett 2004, 851; (b)
Ismaili, H.; Bardajee, G. R. Heteroat. Chem. 2006, 17, 136; (c) Li, Y.; Wang, Y. L.;
Wang, J. Y. Chem. Lett. 2006, 35, 460; (d) Kodomari, M.; Tamaru, Y.; Aoyama, T.
Synth. Commun. 2004, 34, 3029.
26. General procedure for the synthesis of 2-benzyl benzothiazoles (3): To 1 mL of
[bmim]BF4 were added 2-aminothiophenol (1 mmol), phenylacetaldehyde
(1 mmol) and FeCl3Á6H2O (0.1 mmol). The reaction mixture was stirred at
80 °C for 2 h. Upon completion, the mixture was cooled to room temperature
and extracted with ethyl ether (5 mL Â 3). The combined organic phases were
concentrated under vacuum. The crude product was purified by column
chromatography eluting with ethyl acetate/hexane (1–10%) to give the desired
product 3. Details of analytical data of selected compounds are presented as
follows: 3a: syrup (lit.25), 1H NMR (400 MHz, CDCl3) d: 4.45 (s, 2H, CH2), 7.29–
7.39 (m, 6H, ArH), 7.46 (td, 1H, J1 = 7.6 Hz, J2 = 0.8 Hz, ArH), 7.79 (d, 1H,
J = 8.0 Hz, ArH), 8.01 (d, 1H, J = 8.4 Hz, ArH); 13C NMR (100 MHz, CDCl3) d:
40.61, 121.50, 122.76, 124.80, 125.95, 127.33, 128.85, 129.15, 135.66, 137.18,
153.25, 171.18. MS: m/z 226 (MH)+. 3c: syrup, 1H NMR (400 MHz, CDCl3) d:
2.45 (s, 3H, CH3), 4.41 (s, 2H, CH2), 7.24–7.36 (m, 6H, ArH), 7.57 (s, 1H, ArH),
7.86 (d, 1H, J = 8.4 Hz, ArH); 13C NMR (100 MHz, CDCl3) d: 21.43, 40.55, 121.24,
122.21, 127.25, 127.48, 128.80, 129.12, 134.85, 135.81, 137.29, 151.31, 169.99.
MS: m/z 240 (MH)+. HRMS (FAB) calcd for C15H14NS: 240.0848 [M+H], found:
240.0844. 3e: syrup, 1H NMR (400 MHz, CDCl3) d: 4.41 (s, 2H, CH2), 7.04 (t, 2H,
J = 8.4 Hz, ArH), 7.31–7.36 (m, 3H, ArH), 7.46 (td, 1H, J1 = 7.2 Hz, J2 = 0.8 Hz,
ArH), 7.80 (d, 1H, J = 7.6 Hz, ArH), 7.99 (d, 1H, J = 8.4 Hz, ArH); 13C NMR
(100 MHz, CDCl3) d: 39.71, 115.60, 115.82, 121.52, 122.78, 124.90, 126.03,
126.15, 130.64, 130.72, 135.55, 153.22, 170.80. MS: m/z 244 (MH)+. HRMS
(FAB) calcd for C14H11FNS: 244.0597 [M+H], found: 244.0596.