Thermodynamic and orbital studies of the reactivity of amidine with phosphoryl chloride and thionyl chloride

Amidines belong to the family of organic superbases; they are generally considered among the strongest useful synthetic auxiliary bases and are widely used in the synthesis of N-heterocycles. In this present work, we have studied the thermodynamic and the orbital recovery of the cyclization reaction of N'-(1H-benzo[d]imidazol-2-yl)-N-cyclopentylacetamidine 1 towards two reagents: the phosphoryl chloride (POCl3) 2 and thionyl chloride (SOCl2) 3. We were particularly interested in studying the different reactivity of the different sites of attack of the N'-(1H-benzo[d]imidazol-2-yl)-N-cyclopentylacetamidine 1, using density functional theory calculations (DFT) with functional B3LYP and standard base 6-311G. We used all the gathered information either from the experimental results obtained for these reactions or from the theoretical study; to exemplify the reactivity of each active site in our amidine 1, among this particular type of reaction under controlled condition to finally elucidate the mechanism of the obtaining of N-heterocycles such as the [1,2a]benzimidazolo-1,3,5,2-triazaphosphorin-2-oxide 6 and the [1,2a]benzimidazolo-1,2,4,6-thiatriazin-1-oxide 7.