5242
M. Chakrabarty et al. / Tetrahedron Letters 48 (2007) 5239–5242
Yildiz, S.; Go¨ker, H. Bioorg. Med. Chem. 2005, 13, 1587;
2b–h) with stirring a solution of STA (0.058/0.145 g, 2/
5 mol %) in EtOAc (4 mL) at rt. Stirring was continued
until the diamine was consumed (TLC). The mixture was
filtered through a bed of Celiteꢂ, washed with EtOAc
(2 · 10 mL), the pooled filtrates washed with water
(2 · 15 mL) and the organic phase separated, dried and
the solvent removed. The resulting residue was purified by
column chromatography over silica gel using petroleum
(c) Ayhan-Kilcigil, G.; Altanlar, N. Il Farmaco 2003, 58,
1345; (d) Go¨ker, H.; Kus, C.; Boykin, D. W.; Yildiz, S.;
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1
ether–EtOAc as eluent to furnish pure (TLC, H NMR)
11. (a) Brain, C. T.; Steer, J. T. J. Org. Chem. 2003, 68, 6814;
(b) Brain, C. T.; Brunton, S. A. Tetrahedron Lett. 2002,
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12. Wilfred, C. D.; Taylor, R. J. K. Synlett 2004, 1628.
13. Matsushita, H.; Lee, S.-H.; Joung, M.; Clapham, B.;
Janda, K. D. Tetrahedron Lett. 2004, 45, 313.
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Taccone, S. Synlett 2004, 1832.
15. Kozhevnikov, I. V. Chem. Rev. 1998, 98, 171, and
references cited therein.
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18. Preparation of 1-methyl-2-(hetero)arylbenzimidazoles:
General procedure. STA, procured commercially as a
polyhydrate, was heated at ca. 110 ꢁC for 2 h and then
cooled to rt in a desiccator before use. To a solution of 1a/
b/c (1 mmol) and the aldehyde (1.1 mmol) in EtOAc (3–
7 mL) was added dropwise (for 2a, i–r) or all at once (for
products 3a–r,u. Only products 3s and 3t, resulting from
the reaction of 1b with 2a, were separated by preparative
TLC over silica gel. Known products were identified by
comparing their mps and, in some cases, by 1H NMR
spectroscopic analysis. New products were identified by
1
IR, H and 13C NMR, LR and HR EI/FAB-MS.
19. Data of a
representative compound: 1-Methyl-2-(40-
hydroxyphenyl)benzimidazole (3j) (Table 1, entry 10).
Deep brown crystals (0.174 g, 78%); mp 262–264 ꢁC
(EtOAc–MeOH); Rf: 0.49 (petroleum ether–EtOAc, 1:1);
IR (KBr) 3438, 1606, 1441, 1387, 1278, 1245, 1166, 831,
1
736 cmꢀ1; H NMR (500 MHz, DMSO-d6) d 3.82 (s, 3H,
NCH3), 6.93 (d, J = 8.5 Hz, 2H, H-30, 50), 7.19 (dt,
J1 = 7.5 Hz, J2 = 0.5 Hz, 1H, H-5), 7.23 (dt, J1 = 7.5 Hz,
J2 = 0.5 Hz, 1H, H-6), 7.54 (dd, J1 = 7.5 Hz, J2 = 0.5 Hz,
1H, H-7), 7.61 (dd, J1 = 7.5 Hz, J2 = 0.5 Hz, 1H, H-4),
7.66 (d, J = 8.5 Hz, 2H, H-20, 60), 9.98 (br s, 1H, Ar-OH);
13C NMR (125 MHz, DMSO-d6) d 32.5 (NCH3), 111.1
(CH-7), 116.3 (CH-30, 50), 119.4 (CH-4), 121.6 (C-10),
122.5 (CH-5), 122.7 (CH-6), 131.6 (CH-20, 60), 137.4 (C-
7a), 143.3 (C-3a), 154.2 (C-2), 159.6 (C-40); MS (EI) m/z
(%) 224 (M+, 83), 223 (100), 77 (7); HRMS (EI) m/z calcd
for C14H121N2O (M+) 224.0949, found 224.0946. The
individual H and 13C NMR spectral assignments for 3j
were ascertained by analysing its HMQC and HMBC
spectra.
20. Fekner, T.; Gallucci, J.; Chan, M. K. Org. Lett. 2003, 5,
4795.