Reactivity of triplet diradical intermediates in aqueous media for transition-metal-free Csp2–H alkylation

Abstract

Alkyl pyridinium salts have been used in dipolar cycloaddition reactions with π-unsaturated compounds and in reductive single-electron transfer reactions as convenient radical precursors. Here, we report a distinct reaction pathway involving triplet diradical intermediates in the coupling reaction between alkyl pyridinium ylides and electrophilic N -heterocyclic molecules. We demonstrate that alkyl pyridinium ylides generated from alkyl pyridinium salts under basic aqueous conditions can undergo addition into iminoamido N -heterocycles, generating triplet diradical intermediates that can lead to C–H alkylated products. The proposed reaction mechanism is supported by electron paramagnetic resonance and radical scavenging experiments. Notably, a wide substrate scope and excellent level of functional group tolerance are attained under cost-effective and straightforward conditions, which reveal the amenability of this protocol in the pharmaceutical and chemical industries. • Triplet diradical intermediate • C–H alkylation and benzylation • Alkyl pyridinium ylides • Functionalization of N -heterocycles Ghosh et al. report the transition-metal-free C(sp 2 )–H alkylation of N -heterocycles with alkyl pyridinium ylides. The distinct mechanistic pathway in which triplet diradical intermediates are formed by the addition of pyridinium ylides into N -heterocyclic molecules provides an alternative use for nitrogen ylides.