Acidity and N-methylation of N-aryl-N′-cyanoguanidines†

Acid dissociation constants in water have been determined for proton loss from a series of N-aryl-N′-cyanoguanidines 1. Treatment of the same compounds with a strong base, butyllithium, followed by excess methyl iodide leads to successive N-methylation to yield mono-, di- and tri-methylated N-aryl-N′-cyanoguanidines. The mechanism of the methylation is discussed.