Perhaps the best-known ring-expansion reaction is the Baeyer-Villiger oxidation, first reported in 1899- not surprisingly by Adolf von Bayer and Victor Villiger. As we’re all aware, reaction of a carbonyl with a peracid generates a Criegee-type intermediate that undergoes rate-limiting concerted rearrangement to form an ester or lactone. The migration order is substituent dependant, with