Comprehensive Study of the Mechanism of the "Aromatic Nitroso Oxide-Olefin" Interaction as a Function of the Reagents' Structure.

Using reaction model systems (nitroso oxide ArNOO, Ar = Me 2 NC 6 H 4 or O 2 NC 6 H 4 ; exhaustive set of methyl- and cyano-substituted ethylenes), a detailed study of the reaction mechanism of ArNOO with unsaturated compounds was carried out using the density functional theory (M06L/6311 + G(d,p)). The reaction is preceded by the formation of a reagent complex of stacking type, which is favorable for further transformation. Depending on the structure of alkene, the reaction may proceed via two extreme mechanisms: synchronous (3 + 2)-cycloaddition (the most typical case) or one-center nucleophilic attack of the terminal oxygen atom of ArNOO on the less substituted carbon atom of the double bond. The last direction becomes dominant only under special reaction conditions: ArNOO with a strong electron-donating substituent in the aromatic ring, an unsaturated compound with a significantly depleted electron density on C═C bonds, and a polar solvent. In other cases, a different degree of asynchrony in the (3 + 2)-cycloaddition is possible; however, the main intermediate preceding stable reaction products is 4,5-substituted 3-aryl-1,2,3 dioxazolidine in any event. Both thermodynamic and kinetic arguments suggest the most probable decomposition of dioxazolidine into a nitrone and a carbonyl compound. It has been shown for the first time that the polarization of the C═C bond is a powerful factor regulating the reactivity in the reaction under study. The results of the theoretical study show excellent agreement with known experimental data for a wide variety of reacting systems.