(4 + 2) ipso ‐Annulation of para ‐Quinone Methides with Enone‐Tethered Indoles: Access to Spiro(Pyrroloquinoline‐Cyclohexadienone) Scaffolds

An unprecedented base‐mediated formal (4 + 2) ipso ‐cyclization of para ‐quinone methides ( p ‐QMs) with enone‐tethered indoles to provide an extensive array of spiro(pyrroloquinolines‐cyclohexadienones) in good to excellent yield and highly diastereoselective manner bearing two stereocenters, and a quaternary spiro center is described. The tetracyclic 1,7‐fuzed indoles are effectively produced from easily accessible starting materials under mild conditions. The settled protocols feature operational simplicity, high atom economy, gram‐scale synthesis, and postsynthetic modifications. The reaction mechanism is proposed with the support of experimental studies.