Iron(III)-catalyzed tandem annulation of indolyl-substituted p -quinone methides with ynamides for the synthesis of cyclopenta[ b ]indoles.

The unique reactivity of indolyl-substituted p -QMs as a new type of two-carbon synthon has been explored for the first time in a novel iron(III)-catalyzed tandem annulation. This (2+2) annulation/retro-4π electrocyclization/imino-Nazarov cyclization cascade reaction is characterized by an unusual structural reconstruction of indolyl-substituted p -QMs, leading to an expeditious assembly of synthetically important functionalized cyclopenta[ b ]indoles.