Building up quarternary stereocenters of chromans by asymmetric redox organocatalysis: a new entry to vitamin E.

High-turnover catalysis offers a novel concept for the efficient chemo- and enantioselective preparation of chroman intermediates, which are useful for the synthesis of tocopherols (vitamin E components) and other biologically active compounds. A chiral ammonium iodide catalyst mediates the cycloetherification in combination with a cooxidant and an inorganic base in excellent yield and up to 93 % ee. OTs=para-toluenesulfonyl.