Reductive fission of carbon-heteroatom bonds

1 Reductive removal of electronegative o-substituents from ketones, acids and derivatives 

The removal of functional groups from the a-carbon of carbonyl compounds is an important transformation in organic synthesis. Anionic tellurium reagents offer additional useful methods to attain this. 

Sodium hydrogen telluride, sodium 0,0-diethyl phosphorotellurolate, alkali 2-thienyl tellurolates and bis(triphenylstannyl) telluride °/KF reduce a-haloketones to the corresponding ketones. 

The following mechanisms have been proposed to rationalize the described reactions  

Since in method C di(2-thienyl) ditelluride is formed as a by-product and NaBH4 seems to reduce ditellurides preferentially to the carboxyl group, a catalytic procedure can also be employed in which NaBH4 is added to the halo compound in the presence of a catalytic amount (0.1 equiv) of the ditelluride (which is continuously regenerated). 

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