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

A palladium catalyzed Barbier allylation/translactonization cascade reaction was established for the rapid construction of β,γ-disubstituted α-exo-methylene-γ-butyrolactone, an important motif in sesquiterpenes. Dimethyl zinc played significant roles in both steps for umpolung of π-allylpalladium as a nucleophile and promoting a Lewis acid mediated translactonization. This sequence showed 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-seco-guaianolides