Abstract
Differently substituted benzimidazoles have been synthesised in very good yields in solvent-free conditions from o -phenylenediamine and aldehydes in the presence of Yb(OTf)3 as catalyst. The method is applicable to aromatic, unsaturated and aliphatic aldehydes and to substituted o -phenylenediamines without significant differences.
Key words
aldehydes - benzimidazoles - catalysis - lanthanides
References
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13 Typical Procedure.
A mixture of o -phenylenediamine (1 mmol) and aldehyde (1.1 mmol) was well stirred with Yb(OTf)3 (0.05 mmol) at r.t. for 30 min. To this solution, CH2 Cl2 (2 mL) was added to get Yb(OTf)3 crystallized; the catalyst was removed by filtration under reduced pressure and the residue was purified by SiO2 gel column chromatography using CH2 Cl2 -MeOH 99:1 as eluent. Compounds 1 , 2 , 3 , 5 , 6 , 7 , 8 , 9 and 10 were identified by comparison with commercial samples.
2-(2,6-dimethylhept-5-enyl)-1
H
-benzimidazole (
4) . White solid; mp 93-94 °C. 1 H NMR (200 MHz, CDCl3 ): δ = 1.01 (d, 6 H, J = 6.6 Hz), 1.27-2.27 (m, 5 H), 2.67-3.10 (m, 2 H), 5.01-5.21 (m, 1 H), 6.75 (s, 1 H), 7.15-7.65 (m, 4 H). 13 C NMR (50 MHz, CDCl3 ): δ = 18.9, 19.5, 25.5, 25.6, 32.9, 36.9, 37.0, 116.7, 120.2, 122.1, 124.2, 136.3, 142.6, 146.6, 154.2. GC-MS: m/z = 242 [M+ ]. Anal. Calcd for C16 H22 N2 : C, 79.29; H, 9.15; N, 11.56. Found: C, 79.31; H, 9.16; N, 11.54
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