Reactions of 2-aminobenzimidazoles with propiolic esters and diethyl ethoxymethylenemalonate

Electron ionisation induced fragmentation of ethyl 5(1H)‐oxo‐ and 7(1H)‐oxo‐1‐aryl‐2,3‐dihydroimidazo[1,2‐a]‐pyrimidine‐6‐carboxylates: evidence for an unusually regioselective rearrangement of M+• ions

“…These compounds are readily prepared by the annelation of aminoaza heterocycles with diethyl ethoxymethylene malonate (DEEM) 3,. 4 Depending on the heterocyclic system and the reaction conditions, the annelation may either yield mixtures of isomeric products4,, 5 or proceed regioselectively 3…”

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“…We have carried out the reaction of 12 with a representative member of the appropriate esters namely acetoacetate, acetylenedicarboxylate, alkylmalonate and in addition cyanoacetate either in glacial acetic acid or in ethanol in the presence of equivalent quantity of sodium ethoxide at refluxed temperature. In all cases, 4-oxo-tricyclic condensate was isolated as the unique product and on contrary to those instances mentioned [22][23][24], no alternative 2-oxo isomers were formed.…”

Product Class 4: Benzimidazoles

“…The thiol (thione) function is routinely removed by reduction with Raney nickel, but oxidative desulfurizations are also common using reagents such as nitric acid. [51,455,456] Both arylation and acylation are involved when benzimidazol-2-amines undergo copper-catalyzed Ullmann-type reaction with compounds such as 2-chloropyridine-3-carboxylic acid. Milder oxidation with air, iodine, or hydrogen peroxide can give disulfides; more vigorous reaction with peroxide, chlorine, bromine, permanganate, or chromic acid gives the sulfonic acid.…”