Enantioselective total synthesis of the natural gamma-tocopherol metabolite (S)-gamma-CEHC [(S)-LLU-alpha].

The asymmetric synthesis of the natural gamma-tocopherol metabolite (S)-gamma-CEHC (1) is described in 10 steps and 18.4% overall yield starting from 2,3-dimethylhydroquinone. The key step is a stereoselective TiCl(4)-mediated homochiral sulfoxide-directed allylation of ketal (SS)-3 to efficiently generate the challenging C-2 stereogenic carbon of chroman (SS,S)-2 with the correct absolute configuration.