(<i>Z</i>)‑Stereoselective Synthesis of <i>Mono</i>- and <i>Bis</i>-heterocyclic Benzimidazol-2-ones via Cascade Processes Coupled with the Ugi Multicomponent Reaction

Several novel cascade reactions are herein reported that enable access to a variety of unique mono- and bis-heterocyclic scaffolds. The sequence of cascade events are mediated through acid treatment of an Ugi adduct that affords 1,5-benzodiazepines which subsequently undergo an elegant rearrangement to deliver (E)-benzimidazolones, which through acid-promoted tautomerization convert to their corresponding (Z)-isomers. Moreover, a variety of heterocycles tethered to (Z)-benzimidazole-2-ones are also accessible through similar domino-like processes, demonstrating a general strategy to access significantly new scaffold diversity, each containing four points of potential diversification. Final structures of five scaffolds have been definitively proven by X-ray crystallography.