Synthesis of vitamin E.

Vitamin E compounds are biologically essential fat-soluble antioxidants derived from 6-chromanol. This chapter covers the representative literature on the preparation of various stereoisomeric forms and homologues of tocopherols and tocotrienols, and of respective starting materials and intermediates. The industrially most relevant (all-rac)-alpha-tocopherol is generally built up by coupling of arenes with aliphatic precursors. For the synthesis of optically active vitamin E components, various strategies are compiled. In approaches to chiral chroman and side chain building blocks, a broad variety of methods from the repertoire of asymmetric synthesis were applied, that is optical resolution and use of chiral pool starting materials and chiral auxiliaries in stoichiometric as well as catalytic amounts, including catalysis by metal complexes, microorganisms, and enzymes. Most efforts were directed to (2R,4'R,8'R)-alpha-tocopherol due to its prominent biological activity. Syntheses of different stereoisomers (and mixtures thereof) and (beta-, gamma-, delta-) homologues of tocopherols and tocotrienols, as well as methods for their interconversion, are also described.