Metal-free O-H insertion enables access to heterocycle-rich α-carbonyloxy esters

α-Carbonyloxy esters are key structural motifs in bioactive compounds; however, their selective synthesis without metals remains a challenging task, especially in heterocyclic systems bearing reactive sites. Herein, we report a metal and oxidant-free method for synthesizing α-carbonyloxy esters through highly selective O-H bond insertion of aryldiazoacetates with (hetero)carboxylic acids. The transformation occurs under mild thermal conditions and has remarkable selectivity for O-H functionalization in the presence of competing N-H and active C-H bonds. A wide range of substrates, including indole, quinoline, pyrimidine, thiophene, and thiazole derivatives, are well tolerated, affording the desired products in up to 93% yield.