Blue-light-promoted radical C–H azolation of cyclic nitrones enabled by Selectfluor®

Abstract

An original approach to achieve the C(sp²)–H azolation of cyclic aldonitrones mediated by Selectfluor® has first been employed. By exploiting a metal-free, visible-light-promoted cross-dehydrogenative C–N coupling reaction between model aldonitrones, 2H-imidazole 1-oxides, and NH-containing azoles, a series of novel azaheterocyclic derivatives have been obtained in yields up to 94%. The elaborated protocol has proved to be appropriate for gram-scale processes and displayed potential for utilization in the synthesis of novel structural analogues of lanabecestat. Besides, mechanistic studies have revealed that this coupling reaction is likely to proceed via a nitroxide-involving radical pathway, encompassing a chain of electron transfer events, such as hydrogen atom transfer (HAT) and single electron transfer (SET).