Synthetic and Mechanistic Studies into the Rearrangement of Spirocyclic Indolenines into Quinolines

A Density functional theory (DFT) approach has been used to shed light on the mechanism of a recently discovered rearrangement reaction for the conversion of spirocyclic indolenines into cyclopentanone-fused quinolines. A new base-mediated variant of this unusual rearrangement reaction has also been developed, that operates at much lower temperatures than those required in the analogous acidic reactions. The DFT study suggests that both the acid and base-mediated variants proceed via an enol/enolate intermediate, and the ease with which this key intermediate forms appears to be crucial in explaining the kinetic outcomes.