Tellurium anionic reagents

Some tellurium anionic reagents offer a great contribution to these deblocking reactions owing to the use of mild experimental conditions and a non-hydrolytic medium. 

The only structurally characterized derivative of a trisimido organophos-phonate anion is the spirocyclic tellurium(IV) complex (19), which is obtained from the interesting redox reaction between PhPCl2 and [Li2Te(N Bu)3 ] 2 [27]. The phosphorus(V)-centered ligands are generated by imide transfer from tellurium to the phosphorus(III) atoms with concomitant reduction of one-half of the tellurium in the Te(IV) reagent to elemental tellurium [27]. 

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. 

The first reported radical reaction promoted by tellurium reagent was probably the conversion of allylic halides into the coupled 1,5-dienes by treatment with telluride anions. The reaction, which gives the best results when employing the reagent prepared in situ from elemental tellurium and lithium triethylborohydride, proceeds through the intermediacy of the thermally unstable bis-allylic telluride followed by extrusion of tellurium and coupling of the formed allylic radicals. 

It was recently found that selenium dichloride can conveniently be prepared by the reaction of elemental selenium and SO2CI2 It is relatively stable in coordinating solvents and can be used as a reagent for synthetic applications. The attempt to prepare TeCb in the analogous manner from elemental tellurium and SO2CI2 resulted in the formation of various chloridoteUurate anions with different counterions. The solvent and the possible presence of a small amount of residual moisture probably determine the identity of the main product in each individual case. 

Just as sulphur and selenium groups stabilize a-anions, so do tellurium substituents, as shown by the formation of the reagents LiCH3- (TeR) . Some uses for these reagents are shown in Scheme 33. 

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