Synthesis of Spirocyclic γ-Lactones by Cascade Beckwith-Dowd Ring Expansion/Cyclization

A range of spirocyclic gamma-lactones have been prepared exploiting a Beckwith-Dowd ring expansion cascade involving 1-, 3-, 4-, and 5-carbon expansion of cyclopentanone and cyclohexanone followed by 5-exo-trig or 5-exo-dig cyclization. This radical cascade reaction can be achieved with various substrates to provide a broad range of gamma-lactones spirofused to 6- to 10-membered cycloalkanones.