Tellurium nucleophiles

The sulphur, selenium and tellurium nucleophiles required for these SrnI reactions can be generated in a preliminary step by reduction of a sacrificial cathode of graphite mixed with elemental sulphur, selenium or tellurium [160,162]. 

Hi) Sulfur, selenium and tellurium nucleophiles Cleavage of spirooxiranes (e.g. 59) by thiophenol is a key step in a new route to trans-fused y-lactones (Scheme 50) (81TL279). 

Arylation of sulphur, selenium and tellurium nucleophiles by iodonium... 

Arenetellurenyl halides are dihalogen-like electrophiles nucleophiles coordinate with tellurium and generate in many cases linear Y-Te-X arrangements (Y=0, S, Se, Te nucleophile donor atom, X=C1, Br, I). Examples with Se- or Te-containing ligands are not so numerous.9,83... 

The lO-E-4 chalcogen(IV) species diphenylselenium(IV) dibromide (1, Fig. 1) and diphenyltellurium(IV) dibromide (2, Fig. 1) oxidize thiophenol to diphenyl disulfide in nearly quantitative yield as shown in equations (13) and (14). Tellurium(IV) dihalides 6-11 also oxidize thiophenol to diphenyl disulfide and benzene selenol to diphenyl diselenide. Similarly, the 12-Te-5 molecule dioxatellurapentalene 45 (Fig. 19) is a mild oxidant for ethylmercaptan, thiophenol, and benzene selenol giving diethyl disulfide, diphenyl disulfide, and diphenyl diselenide in essentially quantitative yield. As shown in equation (15), 1,1,5,5,9,9-hexachloro-1,5,9-tritelluracyclododecane oxidizes six molecules of thiophenol to diphenyl disulfide and 1,5,9-tritelluracyclododecane in 90% yield. In contrast, 12-Te-5 pertellurane 44 and 12-Se-5 perselenane 46 do not oxidize thiophenol to diphenyl disulfide. Instead, these molecules undergo a nucleophilic addition of thiophenol followed by cleavage of the tellurium-carbon or selenium-carbon bond. ... 

One of the first series of reports on ultrasonically-enhanced electrosynthesis was by Gautheron, Tainturier and Degrand [69] who used the technique to explore routes to organoselenium and tellurium derivatives. Instead of employing a sacrificial cathode of elemental selenium, their procedure allowed the direct use of selenium powder with carbon cloth as cathode to produce Se and Se. A further benefit was that this method also allowed production of the corresponding tellurium anions. These species could be employed in situ in aprotic solvents such as DMF, THF and MeCN for the synthesis of selenides and tellurides by nucleophilic displacement from haloalkanes. 

In this method, the electrophilic tellurium tetrachloride is employed as starting material to introduce tellurium in organic substrates, in contrast to the preceding methods using nucleophilic tellurium species. 

A different approach to unsymmetrical diorganyl tellurides, in which an electrophilic tellurium species is used, involves the nucleophilic attack of organomagnesium or organo-lithium reagents to diorganyl ditellurides. 

Reactions involving the attack of a nucleophilic carbon atom activated by an a-carbonyl group at the electrophilic tellurium atom of tellurium tetrachloride belong to the oldest methods of preparative organic tellurium chemistry. 

During work on nucleophilic substitution at divalent sulfur,64 65 a series of tellurium derivatives with sulfur-containing ligands were prepared in a straightforward manner by addition of a warm aqueous solution of, for example, thiourea to tellurium dioxide dissolved in warm hydrochloric or hydrobromic acid, and which involved the reduction of tellurium(IV) to tellurium(II). 

---