The Baeyer–Villiger oxidation enables the conversion of ketones into esters and cyclic ketones into lactones via oxygen insertion adjacent to the carbonyl group. Developed by Adolf von Baeyer and Victor Villiger in the late 19th century, the reaction proceeds through formation of a Criegee intermediate followed by migratory rearrangement, with group migration governed by migratory aptitude. Learn. Review. Repeat.