π-Electron Donation at the Sulfoximidoyl Nitrogen Atom

Knowledge of the physicochemical properties and the reactivity of functional groups is invaluable in organic chemistry. Although substantial understanding of properties/reactivities exists for standard functional groups, moieties which have entered the chemist's toolbox more recently are often not as well characterized. Sulfoximines constitute such a class of recently strongly promoted compounds, which nowadays have emerged as relevant molecules in an industrial context and in academic research. However, theoretical studies on the properties of the sulfoximidoyl group remain sparse. The aim of the present work was to investigate the interactions of the sulfoximidoyl nitrogen lone pairs with adjacent π-acceptor orbitals. Density functional theory-based (DFT-based) methods were employed throughout the investigation to quantify the strength of these interactions and to characterize their influence on the properties/reactivities of N-functionalized sulfoximines. Although sulfoximines are commonly characterized as electron-withdrawing, our analysis suggests a strong positive mesomeric effect of the sulfoximidoyl group at nitrogen. This effect increases the basicity and nucleophilicity of conjugated substituents at the sulfoximidoyl nitrogen atom.