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‐carboxylates were prepared by a [4 + 2] cycloaddition and their FTIR, 1H, 13C and 15N NMR spectra were measured and assigned. Single crystals were grown for five compounds and their X‐ray data were obtained. The electronic structure and the conformations were calculated by the semi‐empirical AM1 method. Using correlations between the spectral, empirical and theoretical structural data, the transmission of substituent effects and the preferential conformation connected with the consecutive double nitrogen inversion and regarding the mutual orientation of NH and CO bonds were investigated. The results are compared with those for a previously reported series of analogous ethyl 2‐arylcarbamoyl‐4,5‐dimethyl‐1,2,3,6‐tetrahydropyridazine‐1‐carboxylates. Copyright © 2001 John Wiley & Sons, Ltd.