Pyrroloindolone Synthesis via a Cp*Co^III-Catalyzed Redox-Neutral Directed C–H Alkenylation/Annulation Sequence

A unique synthetic utility of a Cp*Co^III catalyst in comparison with related Cp*Rh^III catalysts is described. A C2-selective indole alkenylation/annulation sequence proceeded smoothly with catalytic amount of a [Cp*Co^III(C₆H₆)]­(PF₆)₂ complex and KOAc. Intramolecular addition of an alkenyl-Cp*Co species to a carbamoyl moiety gave pyrroloindolones in 58–89% yield in one pot. Clear difference was observed between the catalytic activity of the Cp*Co^III complex and those of Cp*Rh^III complexes, highlighting the unique nucleophilic activity of the organocobalt species. The Cp*Co^III catalysis was also suitable for simple alkenylation process of <i>N</i>-carbamoyl indoles, and broad range of alkynes, including terminal alkynes, were applicable to give C2-alkenylated indoles in 50–99% yield. Mechanistic studies on C–H activation step under Cp*Co^III catalysis with the aid of an acetate unit as well as evaluation of the difference between organo-Co^III species and organo-Rh^III species are also described

Site- and Regioselective Monoalkenylation of Pyrroles with Alkynes via Cp*Co^III Catalysis

A site-, regio-, <i>syn</i>-, and monoselective alkenylation of dimethylcarbamoyl-protected pyrroles proceeded using a catalytic amount of [Cp*Co­(CH₃CN)₃]­(SbF₆)₂ and KOAc. A variety of internal alkynes with several functional groups and a terminal alkyne afforded hydropyrrolation products in a selective manner in good to excellent yield. The site-selectivity (C2/C5 selectivity) observed for C3-substituted pyrroles is noteworthy because Cp*Rh^III-catalyzed conditions afforded only a moderate yield and low selectivity. The conditions described here provide general and straightforward access to unsymmetrically mono- and disubstituted pyrrole derivatives