Highly congested spiro-compounds via photoredox-mediated dearomative annulation cascade

Abstract

Photo-mediated radical dearomatization involving 5-exo-trig cyclizations has proven to be an important route to accessing spirocyclic compounds, whereas 6-exo-trig spirocyclization has been much less explored. Here, a dearomative annulation cascade is realized through a photoredox-mediated C–O bond activation of aromatic carboxylic acids to produce two kinds of spirocyclic frameworks, whereby the spirocyclizations are triggered by acyl radical formation from benzoic acids leading to spiro-chromanones via a direct intramolecular 6-exo-trig cyclization or spirocyclic lactams via an intermolecular addition/5-exo-trig cyclization cascade.