Enamine Catalytic Annulation of Azonaphthalenes: An Access to Indole Derivatives.

The secondary-amine mediated [3 + 2] annulation of azonaphthalenes with aldehydes and ketones is described for the first time, which provides an alternative protocol for the synthesis of indole derivatives. It features a cheap and readily available catalyst, a broad scope of reactants, very mild reaction conditions, and high efficiency. Significantly different from the transition-metal-mediated processes, the enamine activation represents the first organic base-catalytic protocol for indole synthesis.