2,3-DISUBSTITUTED HEXAHYDRO-QUINOXALINES AND TETRAHYDRO-QUINOXALINES - SYNTHESIS AND A THEORETICAL AND EXPERIMENTAL DYNAMIC NMR-STUDY

The synthesis of 2,3- disubstituted hexahydroquinoxaline stereoisomers from 1,2-diaminocyclohexanes and the corresponding alpha-dicarbonylic derivatives and their oxidation to tetrahydroquinoxalines is describe d. Their H-1- and C-13-NMR spectra are analyzed and a C-13-DNMR study on cis 2,3-diphenyl-hexahydroquinoxaline 1a is carried out. The Delta H, Delta S* and Delta G* for the dynamic process of interchange betwe en the two chair conformers of cis 1a are calculated. A theoretical st udy, using the semiempirical methods AM1 and PM3 of cis and trans 1a, as well as, Ab initio calculations, using 4-31G basis over optimized g eometries by the semiempiric method PM3, of their anlogous without phe nyl substituents are reported. The Delta H values calculated are in a greement with the experimental value for cis 1a.