This work describes acylation reactions facilitated by a type of heterocycle‐based acyl transfer agent, 2‐acyloxypyridazinone. Reactions of 2‐acyloxypyridazinone with carboxylic acids yield mixed carbonic anhydride intermediates, which are reactive and could be coupled with a wide range of substrates including acids, amines, alcohols, and thiols. The wide substrate scope, ease of operation (no additive