New mechanistic-insights into the copper catalyzed ring expansion of vinyl aziridines: evidence in support of a copper(I) mediated pathway

We report how mechanistically inspired metal additive choices result in acceleration of the copper catalyzed vinyl aziridine ring expansion reaction. Most importantly, we demonstrate how the use of in situ reducing agents significantly accelerates the reaction, suggesting a copper(I) active species. These acceleration results were confirmed using Cu(hfacac)(cod) as catalyst. NMR kinetic studies revealed the relative importance of olefin and sulfonamide electronics on the reaction rate and established the order of both catalyst and substrate, which together favored a new copper(I) insertion mechanism.