Cobalt-Catalyzed Oxidant-Free Spirocycle Synthesis by Liberation of Hydrogen

The
first example of oxidant-free cobalt-catalyzed synthesis of
five-membered spirocycles is reported from benzimidates and maleimides
utilizing nitrobenzene as promoter. In contrast to previously known
cobalt-catalyzed oxidative C–H functionalization reactions,
this transformation occurs efficiently in the absence of oxidant and
is accompanied by liberation of hydrogen. The spiro-lactams were readily
achieved by the hydrolysis of as-prepared spirocyclic compounds. The
Cp*Rh­(III) catalyst shows poor reactivity.