An organic thiyl radical catalyst for enantioselective cyclization

A diverse array of chiral organocatalysts have been developed that rely on acid-base interactions to promote enantioselective ionic reactions via the movement of electron pairs. The stereocontrol of radical reactions using organocatalysts is an alternative approach, and several studies have shown that synthetically useful reactivity can result by controlling the movement of single electrons. However, in these studies, it is still an acid-based organocatalyst which forms a closed-shell intermediate with substrate prior to the radical reaction and imparts chiral information, and use of a chiral organic radical directly as catalyst has only rarely been explored. Here, we report the design of an organic thiyl radical catalyst with a carefully designed chiral pocket constructed around a chiral thiol precatalyst. The resulting catalyst was used to effect highly diastereo- and enantioselective C-C bond-forming radical cyclizations.