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

A range of spirocyclic γ-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-<i>exo</i>-trig or 5-<i>exo</i>-dig cyclization. This radical cascade reaction can be achieved with various substrates to provide a broad range of γ-lactones spirofused to 6- to 10-membered cycloalkanones