Temperature switchable Brønsted acid-promoted selective syntheses of spiro-indolenines and quinolines

A high-yielding, temperature switchable divergent approach towards the synthesis of either spiro-indolenines or quinolines is described, starting from easily available indolyl ynones. The application of TFA at rt promotes the dearomatization of the indole, resulting in the formation of the spiro-indolenine, while at higher temperature, rearrangement results in the formation of the quinoline.