Pyrimidine reactions. Part XVII. Ring fission of 1,2-dihydro-2-imino-1-methyl-, 5-methylsulphonyl-, and 5-methylsulphinyl-pyrimidine by amines

Abstract

1,2-Dihydro-2-imino-1-methylpyrimidine is unaffected by a tertiary amine (triethylamine) but in a secondary amine (pure diethylamine) it undergoes Dimroth rearrangement to 2-methylaminopyrimidine. In a primary amine (butylamine but not aniline) it suffers ring fission to give 1,3-dibutyliminopropane, which is shown to exist in an intramolecularly hydrogen-bonded form; in hydrazine hydrate it is converted into pyrazole. 5-Methylsulphonyl- and 5-methylsulphinyl-pyrimidine, which are shown to be covalently hydrated as cations in aqueous solution, undergo analogous ring cleavage in primary alkylamines (pentylamine or benzylamine) to give 2-methyl-sulphonyl-1,3-dipentyliminopropane or an appropriate analogue.