Synthesis, NMR Spectroscopy, and Molecular Modeling of2-Methyl-2,3,4,5-tetrahydro-1H-[1]benzothieno[2,3-c]azepine

A new synthetic approach to fused azepines was demonstrated on an example of the synthesis of 2-methyl-2,3,4,5-tetrahydro-1H-[1]benzothieno[2,3-c]azepine. The key stage of the synthesis is the formation of the azepine ring under the Eschweiler–Clark reaction conditions. The Gibbs energy of activation for the inversion of the azepine ring was determined by dynamic 1H NMR spectroscopy. Molecular modeling of the structure and estimation of the 1H and 13C NMR chemical shifts were performed for 2-methyl-2,3,4,5-tetrahydro-1H-[1]-benzothieno[2,3-c]azepine. The magnetic shielding tensors were calculated by the standard GIAO method using the B3LYP/6-31G(d,p)-optimized molecular geometry parameters. The solvent effect was taken into account in the PCM approximation. The calculated 1H and 13C NMR chemical shifts of 2-methyl-2,3,4,5-tetrahydro-1H-[1]-benzothieno[2,3-c]azepine are in good agreement with the experimental values observed in the spectra of its DMSO-d6 solution.