Total Syntheses of Paraconic Acids and 1,10-<i>seco</i>-Guaianolides via a Barbier Allylation/Translactonization Cascade of 3‑(Bromomethyl)-2(5<i>H</i>)‑furanone

A palladium-catalyzed Barbier allylation/translactonization cascade reaction was established for the rapid construction of β,γ-disubstituted α-<i>exo</i>-methylene-γ-butyrolactone, an important motif in sesquiterpenes. Dimethyl zinc played significant roles in both steps for the umpolung of π-allylpalladium as a nucleophile and promoting a Lewis acid-mediated translactonization. This sequence showed a broad substrate scope and was further harnessed for the synthesis of two paraconic acids as well as the first protecting-group-free total synthesis of two 1,10-<i>seco</i>-guaianolides.