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Y. Yamamoto et al. / Tetrahedron Letters 49 (2008) 876–878
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A.; Yepez, L.; Hernandez-Luis, F.; Navarrete-Vazquez, G.; Tapia, A.;
12. Synthesis of benzimidazoles (Table 2, entry 11): To the mixture of
amidoxime (517 mg, 2 mmol) in CHCl3 (5 mL) was added TEA
(0.697 mL, 5 mmol). The mixture was cooled to ꢀ20 °C, Ts2O was
added (685 mg, 2.1 mmol), and the mixture was stirred at ꢀ20 °C for
5 min. The reaction mixture was allowed to warm to room temper-
ature and was stirred for 1 h. The mixture was then quenched with
H2O (2.5 mL). The aqueous layer was discarded and the organic layer
was dried over Na2SO4 and filtered. The filtered solution was
concentrated under reduced pressure. The residue was purified by
silica gel chromatography to give the benzimidazole product as white
crystals (471 mg, 98%). 1H NMR (400 MHz, DMSO-d6) d 12.13 (br s,
1H), 7.40 (br s, 2H), 7.08 (d, J = 9.5 Hz, 1H), 2.82 (tt, J = 11.5 Hz,
3.4 Hz 1H), 2.47 (s, 3H), 1.99 (br d, J = 12.9 Hz, 2H) 1.76 (dt,
J = 12.9 Hz, J = 3.7 Hz, 2H), 1.63–1.66 (m, 1H), 1.59 (qd,
J = 12.4 Hz, J = 3.0 Hz, 2H), 1.37 (qt, J = 12.2 Hz, J = 3.2 Hz,
2H), 1.26 (tt, J = 12.2 Hz, J = 3.2 Hz, 1H).
´
´
Cortes, R.; Hernandezc, M.; Castilloa, R. Bioorg. Med. Chem. Lett.
2002, 12, 2221–2224; (h) Sondhi, S. M.; Singhal, N.; Johar, M.;
Reddy, B. S. N.; Lown, J. W. Curr. Med. Chem. 2002, 9, 1045–1074;
(i) LaPlante, S. R.; Jakalian, A.; Aubry, N.; Bousquet, Y.; Ferland,
J.-M.; Gillard, J.; Lefebvre, S.; Poirier, M.; Tsantrizos, Y. S.;
Beaulieu, P. L. Angew. Chem., Int. Ed. 2004, 43, 4306–4311.
2. For review, see: Preston, P. N. Chem. Rev. 1974, 74, 279–314.
3. Recent advances in this area: (a) Wang, Y.; Sarris, K.; Sauer, D. R.;
Djuric, S. W. Tetrahedron Lett. 2006, 47, 4823–4826; (b) Lin, S.-Y.;
Isome, Y.; Stewart, E.; Liu, J.-F.; Yohannes, D.; Yu, L. Tetrahedron
Lett. 2006, 47, 2883–2886; (c) Wang, R.; Lu, X.-X.; Yu, X.-Q.; Shi,
L.; Sun, Y. J. Mol. Catal. A: Chem. 2007, 266, 198–201.
4. Recent advances in this area: (a) Curini, M.; Epifano, F.; Montanari,
F.; Rosati, O.; Taccone, S. Synlett 2004, 1832–1834; (b) Lin, S.; Yang,
L. Tetrahedron Lett. 2005, 46, 4315–4319; (c) Gogoi, P.; Konwar, D.
Tetrahedron Lett. 2006, 47, 79–82; (d) Ryabukhin, S. V.; Plaskon, A.
S.; Volochnyuk, D. M.; Tolmachev, A. A. Synthesis 2006, 3715–3726;
(e) Du, L.-H.; Wang, Y.-G. Synthesis 2007, 675–678; (f) Zhang, Z.-H.;
Yin, L.; Wang, Y.-M. Catal. Commun. 2007, 8, 1126–1131.
5. (a) Evindar, G.; Batey, R. A. Org. Lett. 2003, 5, 133–136; (b) Zou, B.;
Yuan, Q.; Ma, D. Angew. Chem., Int. Ed. 2007, 46, 2598–2601; (c)
Zheng, N.; Anderson, K. W.; Huang, X.; Nguyen, H. N.; Buchwald,
S. L. Angew. Chem., Int. Ed. 2007, 46, 7509–7512.
1H NMR data for selected compounds (Table 2, entry 2) H NMR
(400 MHz, DMSO-d6) d 12.98 (br s, 1H), 8.69 (d, J = 4.6 Hz, 1H),
8.28 (d, J = 8.0 Hz, 1H), 7.95 (td, J = 7.6 Hz, 1.4 Hz 1H), 7.44–7.65
(br m, 1H), 7.46 (dd, J = 6.6 Hz, J = 4.9 Hz, 1H), 7.00–7.25 (br m,
1H), 6.86 (br s, 1H), 3.77 (s, 3H).
(Table 2, entry 3) Mixture of tautomers (9:1): 1H NMR (400 MHz,
DMSO-d6) d 13.11 (br s, 0.1H), 13.07 (br s, 0.9H), 8.71 (d, J = 4.6 Hz,
0.9H), 8.70–8.73 (m, 0.1H), 8.30 (d, J = 8.1 Hz, 0.9H), 8.28–8.31 (m,
0.1H), 8.00 (td, J = 7.6, J = 1.5, 0.9H), 7.94–8.00 (m, 0.1H), 7.49
(ddd, J = 7.3 Hz, J = 4.9 Hz, J = 1.0 Hz, 0.9H), 7.47–7.53 (m, 0.1H),
7.29 (d, J = 8.1 Hz, 0.1H), 7.08–7.18 (m, 1.9H), 6.80 (d, J = 7.8 Hz,
0.1H), 6.70 (dd, J = 7.3 Hz, J = 1.2 Hz, 0.9H), 3.96 (s, 2.7H), 3.93 (s,
0.3H).
(Table 2, entry 7) 1H NMR (400 MHz, DMSO-d6) d 12.91 (br s, 1H),
8.15 (d, J = 6.1 Hz, 2H), 7.44–7.59 (br m, 5H),7.16 (dd, J = 8.6 Hz,
J = 2.0 Hz, 1H), 2.53 (s, 3H).
(Table 2, entry 8) Mixture of tautomers (55:45): 1H NMR (400 MHz,
DMSO-d6) d 13.00 (br s, 0.45H), 12.87 (br s, 0.55H), 8.30 (d,
J = 7.1 Hz, 0.9H), 8.15 (d, J = 7.3 Hz, 1.1H), 7.44–7.58 (m, 3H), 7.26
(d, J = 8.0 Hz, 0.45H), 7.07–7.17 (m, 1.55H), 6.79 (d, J = 7.8 Hz,
0.45H), 6.70 (dd, J = 6.3 Hz, J = 2.4 Hz 0.55H), 3.97 (s, 1.35H), 3.96
(s, 1.65H).
6. Partridge, M. W.; Turner, H. A. J. Chem. Soc. 1958, 125, 2086–
2092.
7. (a) Grenda, V. J.; Jones, R. E.; Gal, G.; Sletzinger, M. J. Org. Chem.
1965, 30, 259–261; also see: (b) Ichikawa, M.; Nabeya, S.; Muraoka,
K.; Hisano, T. Org. Prep. Proced. Int. 1978, 10, 205–209; (c)
Ichikawa, M.; Hisano, T. Chem. Pharm. Bull. 1982, 30, 2996–
3003.
8. (a) Sauer, J.; Mayer, K. K. Tetrahedron Lett. 1968, 9, 325–330; (b)
Garapon, J.; Sillion, B.; Bonnier, J. M. Tetrahedron Lett. 1970, 11,
4905–4908; (c) Houghton, P. G.; Pipe, D. F.; Rees, C. W. J. Chem.
Soc., Perkin Trans. 1 1985, 1471–1479; (d) Ramsden, C. A.; Rose, H.
L. J. Chem. Soc., Perkin Trans. 1 1995, 615–617; (e) Ramsden, C. A.;
Rose, H. L. J. Chem. Soc., Perkin Trans. 1 1997, 2319–2327. and
references cited therein.
9. (a) Grundmann, C.; Dean, J. M. J. Org. Chem. 1965, 30, 2809–2810;
(b) Grundmann, C.; Frommeld, H.-C. J. Org. Chem. 1966, 31, 157–
162; For other methods to amidoximes see: (c) Anbazhagan, M.;
Boykin, D. W.; Stephens, C. E. Tetrahedron Lett. 2002, 43, 9089–
9092; (d) Katritzky, A. R.; Khashab, N. M.; Kirichenko, N.; Singh,
A. J. Org. Chem. 2006, 71, 9051–9056. and references cited therein.
10. Imidoyl chlorides used to prepare amidoximes were synthesized using
the following literature: Himo, F.; Lovell, T.; Hilgraf, R.; Rostovtsev,
V. V.; Noodleman, L.; Sharpless, K. B.; Fokin, V. V. J. Am. Chem.
Soc. 2005, 127, 210–216.
(Table 2, entry 10)1H NMR (400 MHz, DMSO-d6) d 12.10 (br s, 1H),
7.13–7.41 (br m, 2H), 6.91 (d, J = 8.0 Hz, 1H), 2.80 (tt, J = 11.5 Hz,
3.4 Hz 1H), 2.37 (s, 3H), 2.00 (br d, J = 12.9 Hz, 2H) 1.76 (dt,
J = 12.9 Hz, J = 3.7 Hz, 2H), 1.63–1.74 (m, 1H), 1.60 (qd,
J = 12.4 Hz, J = 3.0 Hz, 2H), 1.37 (qt, J = 12.2 Hz, J = 3.2 Hz,
2H), 1.26 (tt, J = 12.2 Hz, J = 3.2 Hz, 1H).
(Table 2, entry 12) Mixture of tautomers (3:1): 1H NMR (400 MHz,
DMSO-d6) d 12.44 (br s, 0.75H), 12.08 (br s, 0.25H), 7.51 (d,
J = 7.6 Hz, 1H), 7.47 (d, J = 7.0 Hz, 0.25H), 7.41 (d, J = 7.8 Hz,
0.75H) 6.92 (t, J = 7.8 Hz, 0.75H), 6.91 (t, J = 7.8 Hz, 0.25H), 2.81–
2.94 (m, 1H), 1.93–2.04 (m, 2H), 1.75–1.86 (m, 2H), 1.52–1.75 (m,
3H), 1.24–1.50 (m, 3H).
11. Reactions were monitored by HPLC and intermediates are not
isolated.