Dynamic NMR Study and Detailed 1H and 13C Assignments of an ADAR Precursor in Solvent

A nitrogen-containing compound, named methyl-4-phenyl-2-(2,4,6-triisopropyl-phenylsulfonamido)but-3-enoate (MPSN), is used as a precursor for inverse-electron-demand aza-Diels–Alder reaction. Its 1 H and 13 C nuclear magnetic resonances (NMR) were fully assigned by a combination of one- and two-dimensional NMR experiments. It was found that this compound had two conformers ( a and b ) in the process of assignments. Exchange spectroscopy (EXSY) was used to study the exchange dynamics of this compound in solvent. On the basis of 1 H NMR and EXSY experiments at various temperatures, thermodynamic and dynamic parameters of the conformational exchange process were deduced for this compound. The free-energy activation (Δ G ≠ ) at 298 K is 15.07 ± 0.6 kcal mol −1 , which suggests that the conformational exchange might be the result of C=N bond rotation.