1,2- and 1,3-Diamine exchange between substituted 4,5-dihydroimidazoles and 1,4,5,6-tetrahydropyrimidines: routes to benzimidazoles, dihydroimidazoles, and tetrahydropyrimidines

Abstract

A range of 2-substituted 4,5-dihydroimidazoles and 2-substituted 1,4,5,6-tetrahydropyrimidines when heated with an excess of substituted ethane-1,2-diamines, o-phenylenediamines, and propane-1,3-diamine underwent diamine exchange to give 2-substituted heterocycles derived from the solvent diamine. The reaction was an equilibrium process favouring six-membered rings. The synthetic scope is amplified by the ready aromatisation of these partially reduced heterocycles.