Stereoselective (exo-specific) synthesis, dynamic 1H NMR and quantum chemical conformational and configurational analysis of norbornene-aziridine-E-imidoyl system

Abstract

Open image in new window Stereoselective (exo-specific) synthesis, dynamic 1H NMR and computational analysis of exo-N′-{3-azatricyclo[3.2.1.0.2,4]oct-3-yl)mesithyloxy)methylene}-1-benzensulfunamide (3) were investigated. Aziridine nitrogen inversion gives rise to two sets of configurations where the N-substituent is Syn (S) or Anti (A) to C7 of the norbornyl ring. At lower temperature, the proton signals of aziridine exo-E-3 decoalesces to show two syn conformers and one anti conformer (exo-E-3 1 S \( \leftrightharpoons \) exo-E-3 2 S \( \leftrightharpoons \) exo-E-3 3 A ) with ratio of 60:20:20, respectively. Experimentally, the Gibbs free energy of activations [ΔG‡ (kcal/mol) ± 0.08] were calculated 11.96, 12.45 for 3 isomerizations. The standard Gibbs free energy (ΔGo kcal/mol) 0.174, 0, 0.174, and 0.298 at 213 K and energy minimum 6.64, 4.77 and 1.78 were calculated for 31S \( \leftrightharpoons \) 32S, 32S \( \leftrightharpoons \) 3 3 A , 3 1 S \( \leftrightharpoons \) 3 3 A isomerizations, respectively. The enthalpy (ΔH‡, kcal/mol) and entropy (ΔS‡, cal mol−1 K−1) of activation for the nitrogen inversion of aziridine of 3 were calculated 11.2 and −0.80, respectively.