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(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*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-CoIII species and organo-RhIII species are also described.本文报道了相较于同类五甲基环戊二烯基铑(III)（Cp*RhIII）催化剂，五甲基环戊二烯基钴(III)（Cp*CoIII）催化剂独特的合成应用价值。在催化量的[Cp*CoIII(C6H6)](PF6)2配合物与乙酸钾（KOAc）存在下，吲哚的C2选择性烯基化/环化序列可顺利进行。烯基-Cp*CoIII物种对氨基甲酰基的分子内加成反应，可通过一锅法以58%~89%的收率得到吡咯并吲哚酮类产物。研究观察到Cp*CoIII配合物与Cp*RhIII配合物的催化活性存在显著差异，凸显了有机钴物种独特的亲核活性。Cp*CoIII催化体系同样适用于N-氨基甲酰基吲哚的简单烯基化过程，包括端炔在内的多种炔烃均可适用，以50%~99%的收率得到C2位烯基化吲哚产物。本文还报道了在乙酸单元辅助下Cp*CoIII催化C-H活化步骤的机理研究，以及有机钴(III)物种与有机铑(III)物种间活性差异的评价。