Organotellurides

Oxidation of thiols and related compounds with organoselenium(IV) and organotellurium(rV) compounds 102 Other oxidations with selenoxides and telluroxides 106 Thiolperoxidase and haloperoxidase-like activity of organoselenides and organotellurides 108... 

The dendrimer wedges with two, three, and four organotelluride groups and the first-generation Frechet-type dendrimers based on 3,5-dihydroxybenzyl alcohol and l,l,l-tris-4-hydroxyphenylethane shown in Fig. 26 illustrate statistical effects in thiolperoxidase-like reactions. Nearly linear increases in reactivity on a molar basis with increasing numbers of organotelluride groups were observed in the oxidation of... 

Because of the weak C-Te bond, organotellurides can serve as efficient carbon radical precursors [13]. However, they are generally unstable to handle, unlike the... 

More recently organotellurides have been used for the stereoselective debromination of vic-dibromides. ... 

The organotelluride salt (28) readily dehalogenates a variety of a-halocarbonyl compounds, including ketones, acids and esters. It is not clear whether the first step is displacement of halide to afford an a-tellurocarbonyl compound, followed by attack upon the latter by (28), or whether (28) attacks the a-sub-stituent directly. Reduction can be effected by NaBH4 containing a catalytic quantity of (28). ... 

Further reports describe the use of the Ni(PEt3)4 system in the presence of phosphines as a successful catalyst for the detelluration of organotellurides and ditellurides. ... 

From this data, one can see why alkyl iodides are generally more reactive than bromides, which in turn are more reactive than chlorides in atom transfer reactions. Likewise, phenyl tellurides are more reactive than phenyl selenides. In general, the rates of atom transfer to alkyl radicals from organoiodides are comparable to those from organotellurides. Comparable rates of atom transfer are also observed for bromides and phenyl selenides. Chlorides are not as useful in atom transfer addition reactions because of their comparatively slow rates of atom transfer, and atom transfer reactions of phenyl sulfides are not commonly observed. 

Alkyl radicals, generated from Barton esters or organotellurides, add to the diazirine present in large excess (20 equivalents). After dimerization of the radical adducts and nitrogen extrusion, imines were isolated. Hydrolysis with boric acid followed by acetylation afforded the corresponding acetamides (Scheme 22). 

Sodium borohydride-aqueous base. Enone reduction. 2,6-Di-t-butyl- Formation of aryl radicals. Redn intermediates. Addition to a side-chain 6 Organotelluride anions. Ditellun are useful for phenylseleno removal front... 

Organotelluride anions. Ditellurides are reduced to generate the anions that are useful for phenylseleno removal from the a-position of a carbonyl group. 

In the DT process, P-X is attacked by a polymer radical to form another polymer radical. The X in this process involves iodide [13], dithioesters [14], organotellurides [15], and organostibine [16]. The polymerization using dithioester as X is often called reversible addi-hon fragmentahon chain transfer (RAFT), and the polymerization using a tellurium compound as X is termed organotellurium-medi-ated radical polymerization (TERP). 

Organotellurides 1 have been used in debromination of vicinal (vie) dibromides. The reaction takes place by heating the dibromide and the organotelluride in CHCI3 or CH3CN at 90-100°C as shown in Scheme 29.1. 

Both mechanisms are overall second-order processes involving organotelluride and dibromide, and could fit well with the experimental rate law. 

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