Synthesis, NMR characterization andab initio6-31G* study of 1-aryl-2,3-dialkyl-1,4,5,6-tetrahydropyrimidinium salts

Abstract

We describe the synthesis of a series of 1-aryl-2,3-dialkyl-1,4,5,6-tetrahydropyrimidinium salts 1, by alkylation of the corresponding 1,4,5,6-tetrahydropyrimidines 2. We analyze the changes in the 1 H and 13 C NMR spectra of compounds 2 induced by protonation and quaternization. The results of an ab initio theoretical study on amidine 2a, and the cations resulting from its protonation (2aH + ) and quaternization (1a + ) are presented. A qualitative correlation was found between 13 C NMR and theoretical data in the case of protonation. The influence of the substitution patterns in the 1 H and 13 C NMR spectra of compounds 1 is also discussed.