Titanium based redox catalyst using

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

The advantage of the above two methods are high yields of epoxides, and the titanium silicalite catalyst is not deactivated or poisoned by the contaminants in the crude oxidation mixture. Hence, the processes are commercially attractive. The in situ hydrogen peroxide generation based on the AO process from either the anthraquinone/anthrahydroquinone or ketone/alcohol redox couples has also been used for the following synthetic reactions ... 

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