Total Synthesis of (±)-Herbertenolide by Stereospecific Formation of Vicinal Quaternary Centers in a Crystalline Ketone

The sesquiterpene (±)-herbertenolide was synthesized in seven steps from commercial 2-bromo-4-methylanisole. In the key step, two adjacent stereogenic quaternary centers were controlled by a highly chemoselective and stereospecific photodecarbonylation reaction of crystalline methyl-trans-3-(2-methyl-5-methoxyphenyl)-1,3-dimethyl-2-oxocyclohexancarboxylate (3). An efficient generation of radical pairs and the stereochemical control exerted by the solid state suggest that this reaction may become a useful synthetic method.