REACTION OF 2-BROMO 2-ALKENOIC CARBONYL-COMPOUNDS WITH AMIDINES - EXPERIMENTAL AND THEORETICAL (PM3) STUDIES OF THE MECHANISM OF HETEROCYCLIZATION INTO DIHYDROIMIDAZOLE AND PYRIMIDIN-4(3H)-ONE

Different pathways have been considered to describe heterocyclisation between monosubstituted or unsubstituted amidines and 2-bromo 2-alkeno ic 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 an alysed. From both thermodynamic and kinetic arguments, it appears that a mechanism involving a pyrimidinone intermediate is more probable th an one in which the intermediate is an aziridine. Solvent effects have been estimated and they do not seem to modify substantially these con clusions.