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Coupling N–H Deprotonation, C–H Activation, and Oxidation: Metal-Free C(sp3)–H Aminations with Unprotected Anilines

Evoniuk, Christopher J., Gomes, Gabriel dos Passos, Hill, Sean P., Fujita, Satoshi, Hanson, Kenneth, Alabugin, Igor V.
Journal of the American Chemical Society 2017 v.139 no.45 pp. 16210-16221
acidity, amination, aromatic compounds, carbon-hydrogen bond activation, chemical bonding, dimethylformamide, heterocyclic nitrogen compounds, oxidants, oxidation, oxygen, transition elements
An intramolecular oxidative C(sp³)–H amination from unprotected anilines and C(sp³)–H bonds readily occurs under mild conditions using t-BuOK, molecular oxygen and N,N-dimethylformamide (DMF). Success of this process, which requires mildly acidic N–H bonds and an activated C(sp³)–H bond (BDE < 85 kcal/mol), stems from synergy between basic, radical, and oxidizing species working together to promote a coordinated sequence of deprotonation: H atom transfer and oxidation that forges a new C–N bond. This process is applicable for the synthesis of a wide variety of N-heterocycles, ranging from small molecules to extended aromatics without the need for transition metals or strong oxidants. Computational results reveal the mechanistic details and energy landscape for the sequence of individual steps that comprise this reaction cascade. The importance of base in this process stems from the much greater acidity of transition state and product for the 2c,3e C–N bond formation relative to the reactant. In this scenario, selective deprotonation provides the driving force for the process.