Investigation of benzimidazole derivatives

Product Class 4: Benzimidazoles

“…[17] Similarly, 5-halobenzimidazoles are easily 4-brominated. [374] Anionic sulfur species 2-substitute 1-alkoxybenzimidazoles, the corresponding 3methylbenzimidazolium salts, and 1-alkylbenzimidazole 3-oxides with simultaneous deoxygenation. [368] Nevertheless, monobromination of 1H-benzimidazole 97 in the 2-position can be achieved in 67% yield using N-bromosuccinimide supported on silica gel giving 99.…”

“…This change in orientation of substitution may be a consequence of the solid support holding the 2-position of the benzimidazole in close proximity to the activated N-bromosuccinimide. [377] 1H-benzimidazol-2(3H)-one: [374] A soln of 1-(ethoxyethyl)-3-methoxybenzimidazolium chloride (1.45 g, 6 mmol) was heated under reflux for 5 h with H 2 O (30 mL). With two equivalents of N-bromosuccinimide, 2,5-dibromo-1H-benzimidazole 99 is formed in 60% yield (see Scheme 49).…”

“…[3,7] The reactions usually occur more readily and give better yields if heated in N,Ndimethylaniline rather than in xylene. [374] Hydrazine reacts with 1-methyl-1H-benzimidazole 3-oxide to give 2-hydrazino-1methyl-1H-benzimidazole. Branching alkyl groups at N1 retard the reaction a little, but the use of excess sodium amide and longer reaction times offset this, except with 1-tert-butyl-1H-benzimidazole.…”

“…1-(Ethoxymethyl)-1H-benzimidazol-2-amine (101, R 1 = CH 2 OEt; R 5 = H): [374] 1-(Ethoxymethyl)-3-methoxybenzimidazolium chloride (6.06 g, 25 mmol) was added in portions to liq NH 3 (200 mL) Electrophilic nitration of benzimidazoles involves the benzimidazolium species and occurs preferentially in the fused homocyclic ring at C5 (6). [384] For example, 1H-benzimidazol-2-amine forms the 5-nitro derivative initially and then the 5,6-dinitro species.…”

Synthesis of 2-Imidazolones and 2-Iminoimidazoles

“…20, 21 While these observations do not prove that the 2-chloroimidazolium salt is formed in the course of the oxidation, they demonstrate that it is a competent intermediate in this chemistry. In the latter case, hydoxide adds to the imidazolium salt 15 to form 19 , 22 O -chlorination and then base-induced elimination of HCl from 20 results in the formation of the carbonyl moiety. Alternatively, with hypochlorite ion (either produced in situ or added directly), this may give species 20 directly, which upon base-induced elimination provides the corresponding imidazolone.…”