Enantioselective synthesis of (2R,4'R,8'R)-alpha-tocopherol (vitamin E) based on enzymatic function

Syntheses of (S)-chroman-2-carboxaldehyde congener 1 and (S)-chiral isoprene unit 3 were achieved based on the enzymatic acetylation of (+/-)-chroman-2-methanol 6 and (+/-)-(2,3)-anti-2-methyl-3-(p-methoxyphenyl)-1,3-propane diol 12, respectively. Synthesis of the side-chain part corresponding to (3R,7R)-3,7,11-trimethyldodecan-1-ol 27 was achieved by the coupling reaction of (S)-3 and (R)-3,7-dimethyloctyl iodide 4. The Wittig reaction of (3R,7R)-phosphonium salt 2 derived from (3R,7R)-27 and (S)-1 gave the olefin 28 which was subjected to catalytic hydrogenation to afford (2R,4'R,8'R)-alpha-tocopherol.