Pyrroloindolone synthesis via a Cp*CoIII-catalyzed redox-neutral directed C-H alkenylation/annulation sequence
A unique synthetic utility of a Cp*CoIII catalyst in comparison with related Cp*RhIII catalysts is described. A C2-selective indole alkenylation/annulation sequence proceeded smoothly with catalytic amount of a [Cp*CoIII(C6H 6)](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*CoIII complex and those of Cp*RhIII complexes, highlighting the unique nucleophilic activity of the organocobalt species. The Cp*CoIII catalysis was also suitable for simple alkenylation process of N-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*CoIII catalysis with the aid of an acetate unit as well as evaluation of the difference between organo-Co III species and organo-RhIII species are also described.
Regioselective C2 oxidative olefination of indoles and pyrroles through cationic rhodium(III)-Catalyzed C-H bond activation
Be economic with your atoms! An efficient Rh-catalyzed oxidative olefination of indoles and pyrroles with broad substrate scope and tolerance is reported (see scheme). The catalytic reaction proceeds with excellent regio- and stereoselectivity. The directing group N,N-dimethylcarbamoyl was crucial for the reaction and could be removed easily. Copyright
Ruthenium-catalyzed regioselective C2 alkenylation of indoles and pyrroles via C-H bond functionalization
An efficient ruthenium-catalyzed oxidative coupling of indoles and pyrroles with various alkenes at the C2-position assisted by employing the N,N-dimethylcarbamoyl moiety as a directing group is reported. The catalytic reaction proceeds in an excellent regio- and stereoselective manner.