Preparation from a-aminoacetals

The acetal (0.01 mol) is heated with the imidate (0.01 mol) in glacial acetic acid (0.02 mol) at 100°C (3h). Aqueous sodium hydroxide is added to form a dark-coloured basic solution which is extracted with diethyl ether, and the extracts are dried and rotary evaporated to give a residue (an oil in the case of a-benzamidinoethanal diethyl acetal). Heating with 5 M hydrochloric acid (4 ml) for 0.5 h. addition of water, and evaporation under reduced pressure again gives a residue which, after being dissolved in water, is extracted with ether to remove any amides (e.g. benzamide in the case of benzimidate). 

Basificaiion with aqueous alkali and re-extraction with ether, drying, and removal of the solvent gives the imidazole. Recrystallization may be necessary. Prepared in this way have been 2-pentyl- (75%), 2-phenyl- (85%), 1-methyl-2-pentyl- (33%) and 1-methy 1-2-phenyl- (42%) imidazoles. 

2-alkyl- or 2-substituted alkylimidazoles [12-15], imidazole 2-carbaldehyde (5) [16] and 5-aminoimidazole-2-carboxylates (8) [17]. Concentrated sulfuric acid induces cyclization of alkyl or aryl amidines, but if the alkyl group is large, dilute acid suffices [14, 15]. 

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