Fast and scalable continuous flow synthesis of butenolides and coumarins†

Herein, we present a versatile and efficient continuous flow protocol for the synthesis of structurally diverse butenolides and coumarins through the in situ generation of acylketenes via the retro hetero-Diels–Alder reaction of dioxinones with α-hydroxy-ketones and salicylaldehydes, respectively. This protocol enabled the synthesis of 5 examples of butenolides with yields ranging from 30 to 91% and 16 examples of coumarins with yields ranging from 30 to 99%. The versatility and practicality of the protocol were demonstrated by the gram-scale synthesis of a biologically relevant γ-spiro butenolide core, as well as the production of benzo-coumarins. Modern medicinal chemistry demands both scalability and the ability to synthesize structurally diverse compounds in a single synthetic platform, and our methodology effectively addresses these challenges in a fast and safer manner.