Stepwise Cross-Couplings of a Dibromo-(gamma)-methylenebutenolide as an Access to Z-Configured (alpha)-Alkenyl-(gamma)-alkylidenebutenolides. Straightforward Synthesis of the Antibiotic Lissoclinolide

The Z-isomer of (alpha)-bromo-(gamma)-(bromomethylene)butenolide was prepared from (alpha)-angelica lactone or levulinic acid in three and four steps, respectively. Successive Stille-couplings with an unsaturated stannane, with the potential to use a different second unsaturated stannane, involved the (gamma)substituent first and the (alpha)-substituent thereafter. Thereby, (alpha)-alkenyl-(gamma)alkylidenebutenolides and their arene analogs were obtained Z-selectively.