Synthesis, dynamic 1H NMR and theoretical study of aryl-nitrogen single bond rotational energy barriers in highly functionalized 4H-chromenes

Abstract

The reactive intermediate was generated by reaction between 2,6-dimethylphenyl isocyanide and dialkyl acetylenedicarboxylates to react with ß-diketones such as 1,3-cyclohexanedione or 5,5-dimethyl-1,3- cyclohexanedione to produce the dialkyl 2-(2,6-dimethylphenylamino)-5-oxo-5,6,7, 8-tetrahydro-4H-chromene-3,4-dicarboxylate in fairly high yields 2a-c. The 1H NMR spectra of these compounds exhibited dynamic effects that are attributed to restricted rotation around the aryl-nitrogen single bond. The calculated rotational energy barrier (ΔG=) for their interconversion of these compounds equals (57.2, 54.0 and 55.7)±2 kJ.mol-1, respectively. In addition, theoretical study on the basis of rotation around the aryl-nitrogen single bond was investigated using ab intio method at HF/6-31G level theory. The theoretical rotational energy barrier for these interconversion were in a good agreement with the experimental rotational energy emerged from dynamic1H NMR data. © ARKAT USA, Inc.