Stereoselective Syntheses of the 2-Isopropenyl-2,3-dihydrobenzofuran Nucleus: Potential Chiral Building Blocks for the Syntheses of Tremetone, Hydroxytremetone, and Rotenone

The first enantioselective synthesis of the 2-isopropenyl-2,3-dihydrobenzofuran skeleton of tremetone and hydroxytremetone from (E)-4-(2-hydroxyphenyl)-2-methyl-2-butenyl methyl carbonate and (E)-4-(2,6-dihydroxyphenyl)-2-methyl-2-butenyl methyl carbonate, respectively, is described. The key step is a catalytic palladium-mediated reaction in the presence of the chiral Trost ligand.