Y-tocotrienyl acetate

The hydrogenation of y-tocotrienyl acetate, a vitamin E precursor [43], is a striking example demonstrating the potential of these catalysts. With complex 27 all three double bonds in the side chain were reduced with very high enantio- and diastereoselectivity to give the natural (R,R,R)-isomer of y-tocotrienyl acetate almost exclusively. Complexes... 

The stereocentres in the terpenoid side chain of the tocopherols, fat soluble antioxidants which are the main components of vitamin E, have been installed using this chemistiy in an impressive demonstration of the power of this methodology. " Various iridium catalysts were screened for the hydrogenation of y-tocotrienyl acetate 19 with pyridine-phosphinite ligand 20 giving almost exclusively the natural (J )-isomer of y-tocopherol acetate 21 (Scheme 14.7). The presence of the existing stereocentre in the molecule exerts almost no influence over the reaction, as demonstrated by hydrogenation with an achiral iridium catalyst. 

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