A novel 1,3-dimethyl-1,3-di-(1-adamantyl)formamidinium perchlorate has been prepared via the Vilsmeier-Haack reaction of N-methyl-N-(1-adamantyl)formamide and N-methyl-N-(1-adamantyl) amine in a mixture of phosphorus oxychloride and benzene. The new formamidinium salt was found to undergo addition-elimination reactions when treated with sodium hydride in acetonitrile or propionitrile solution, thereby forming the corresponding beta-[methyl(1-adamantyl)amino]acrylonitriles and N-methyl-N-(1-adamantyl) amine. The H-1 and C-13 NMR spectra and the single-crystal X-ray structure of the new formamidinium salt have been determined along with those of the related compound 1,3-di-(1-adamantyl)-1-cyanoamidine and the corresponding beta-(dialkylamino)acrylonitriles.