Structural study of ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates: conformation and transmission of substituent effects across the diazabicycloheptene ring

Nine new ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxyl ates were prepared by a [4+2] cycloaddition and their FTIR, H-1, C-13 and N -15 NMR spectra were measured and assigned. Single crystals were crown for five compounds and their X-ray data were obtained. The electronic structure and the conformations were calculated by the semi-empirical AMI method. Us ing correlations between the spectral, empirical and theoretical structural data, the transmission of substituent effects and the preferential conform ation connected with the consecutive double nitrogen inversion and regardin g the mutual orientation of N-H and C=O bonds were investigated. The result s are compared with those for a previously reported series of analogous eth yl 2-arylcarbamoyl-4,5-dimethyl-1,2,3,6-tetrahydropyridazine-1-carboxylates . Copyright (C) 2001 John Wiley & Sons, Ltd.