Asymmetric Synthesis of Natural Product Inspired Tricyclic Benzopyrones by an Organocatalyzed Annulation Reaction

Going back to nature: Electron-deficient oxadienes and electron-poor acetylene carboxylates react in the presence of an organocatalyst to give natural product inspired tricyclic benzopyrones efficiently (up to 99 % yield) and stereoselectively (up to 87 % ee; see scheme). This efficient and operationally simple asymmetric annulation involves the generation of zwitterions from acetylene carboxylates.