Bamberger Fission and Reclosure of 1-Alkyl-5-(alkylamino)imidazole-4-carbonitriles Leading to Their 2-Oxo Derivatives

1-Methyl-5-(methylamino)imidazole-4-carbonitrile (4a) afforded three minor ring-opened products (5a, 6a, 10a) besides its 2-oxo derivative 3a on treatment with ethyl chloroformate in aqueous sodium bicarbonate. The geometrical isomers of these trisubstituted propenenitriles (5a, 6a, 10a) can be separated from each other by means of TLC, but equilibrate rapidly in solution. Because these compounds were converted into 3a in aqueous sodium hydroxide, alkaline treatment of the reaction mixture of 4a afforded a higher yield of 3a; although 3a also rapidly changed into other compounds in 0.1 N aqueous sodium hydroxide at room temperature, it could be recovered from the solution in high yield.5-Alkylamino homologues 3b, c were also prepared in 64% and 46% yields, respectively, by similar treatment of the substrates 4b, c having the 5-alkylamino substituents. The same products 3b, c were obtainable from the positional isomers 4d, e in 83% and 51% yields, respectively. These outcomes are interpretable by supposing that the reactions proceed through common intermediates, equilibrated mixtures of (E)- and (Z)-[2-(alkylamino)-1-cyano-2-(methylamino)ethenyl]carbamic acid ethyl esters (7).