A Dearomatization/Debromination Strategy for the [4+1] Spiroannulation of Bromophenols with α,β‐Unsaturated Imines

A novel [4+1] spiroannulation of o‐ & p‐bromophenols with α,β‐unsaturated imines has been developed for the direct synthesis of a new family of azaspirocyclic molecules. Notably, several other halophenols (X=Cl, I) were also applicable for this transformation. Moreover, a catalytic asymmetric version of the reaction was realized with 1‐bromo‐2‐naphthols by using a chiral ScIII/Py‐Box catalyst. Mechanistic studies revealed that this domino reaction proceeded through electrophile‐triggered dearomatization of phenol derivatives at their halogenated positions and followed by halogen‐displacement with N‐nucleophiles via a radical‐based SRN1 mechanism. An unprecedented [4+1] spiroannulation of halophenols with α,β‐unsaturated imines has been developed for the rapid assembly of highly valuable azaspirocycles. This intermolecular domino reaction was realized through a sequence of electrophile‐triggered dearomatization of phenol derivatives at their halogenated sites and followed by halogen‐displacement with N‐nucleophiles via a radical‐based SRN1 mechanism.