Reaction of 2-bromo 2-alkenoic carbonyl compounds with amidines: experimental and theoretical (PM3) studies of the mechanism of heterocyclisation into dihydroimidazole and pyrimidin-4(3H)-one

Abstract

Different pathways have been considered to describe heterocyclisation between monosubstituted or unsubstituted amidines and 2-bromo 2-alkenoic carbonyl compounds, giving pyrimidin-4(3H)-one or dihydroimidazole heterocycles. Semi-empirical calculations (PM3) have been carried out on the reactants and intermediates. The transition states have been analysed. From both thermodynamic and kinetic arguments, it appears that a mechanism involving a pyrimidinone intermediate is more probable than one in which the intermediate is an aziridine. Solvent effects have been estimated and they do not seem to modify substantially these conclusions.