With diaryl tellurium dihalides

Diaryltellurium diiodides afford the iodocyclization of 4-pentenol. Diaryltellurium dibromides give only traces of bromotetrahydrofurans with 3-butenol and 4-pentenol.  

Typical procedure7 A solution of 4-pentenol (0.0860 g, 1.00 mmol), bis(p-chlorophenyl) tellurium diiodide (0.605 g, 1.00 mmol), and pyridine (0.080 g, 1.00 mmol) was heated at reflux in 10 mL of chloroform for 4 days. The reaction mixture was concentrated in vacuo, and the residue was purified via chromatography on silica gel eluted with 1 1 hexane/ethyl acetate to give 0.121 g (57%) of the iodotetrahydrofuran and 0.30 g (85%) of the diaryl-telluride. 

The synthetic utility of the described reactions is clearly illustrated by the reductive detel-luration of telluroethers with BujSnH, the entire telluration/detelluration process providing a cyclization under mild conditions for unsaturated alcohols. 

Additional synthetically usefnl transformations are given in seqnence. 

Reductive detelluration of cyclic dichlorotelluroethers (general procedure) This procedure is identical to that described for dichlorotellurolactones (see Section 4.5.1.5). 

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Aryl tellurium trichlorides are easily converted to symmetrical or unsymmetrical diaryl tellurium dihalides via reactions with organometallic compounds (see p. 549). Trimethyl(aryl)silanes transfer only the aryl group to tellurium1. 

The reactions between Grignard reagents and tellurium dihalides frequently reported in the older literature (Vol. IX, p. 1051) produced mixtures of diaryl tellurium products and other organic tellurium compounds that were difficult to separate. Tellurium dihalides are rather unstable compounds with a strong tendency to disproportionate to tellurium and tellurium tetrahalides. The Grignard reagents, which had to be used in excess of the stoichiometri-cally required amounts, then reacted with the tellurium (p. 172) and the tellurium tetrahalide and probably not with the tellurium dihalide. 

Diaryl ditellurium compounds and aryl tellurium trihalides react in refluxing 1,2-dichloroethane to form diaryl tellurium dihalides and tellurium. The reactions are postulated to proceed via aryl tellurium halides that disproportionate into tellurium and diaryl tellurium dihalides. All reactions of this type thus far carried out on a preparative scale used pairs of reagents with the same aryl group2. 

Aryl tellurium trichlorides and tribromides condense with methoxybenzene4,5, 1,3-dihydroxybenzene, and dimethylaniline6 to give unsymmetrical diaryl tellurium dihalides. The condensations occur with the hydrogen atom in the para-position to the activating group in the aromatic compound. Aryl tellurium triiodides did not react6. 

Diaryl tellurium compounds are converted to diaryl tellurium dihalides through reactions with sulfur tetrafluoride1, triaryl bismuth difluorides2-3, copper(II) halides4,5, iron(III) chloride, and mercury(II) chloride4. 

Some diaryl tellurium dihalides did not give diaryl tellurium halide hydroxides upon treatment with boiling water, but instead deposited the anhydrides3. 

Diaryl tellurium dihalides in toluene solutions reacted with aryl magnesium bromides in diethyl ether to yield triaryl telluronium salts in yields ranging from 6 to 78% (Vol. IX, p. 1082/3)3-5. Aqueous solutions of the products were generally treated with potassium iodide to convert the telluronium halides to telluronium iodides3,4. 

Diaryl tellurium dihalides condense with 5,5-dimethyl-l, 3-dioxocyclohexane in benzene in the presence of triethylamine to give cyclohexylidene diaryl tellurium compounds. Whether a reaction occurs at 20° or requires elevated temperatures is determined by the substituents on the aryl groups. Dimethyl tellurium dichloride and aryl methyl tellurium dichlorides react at 20°. 

Similarly prepared were the following diaryl tellurium dihalides starting with diphenyl ditellurium or bis[4-fluorophenyl] ditellurium ... 

Diorganotetrahalotellurates were prepared by combining diaryl tellurium dihalides, pentamethylene tellurium diiodide or tetramethylene tellurium diiodide with onium halides. These compounds were found to be 2 1 electrolytes by conductivity and molecular mass measurements. ... 

Reductions of diorgano tellurium dihalides with hydrazine or hydrazine hydrate are carried out in ethanol. Diaryl, alkyl aryl, and dialkyl tellurium dihalides have been reduced in this manner. The isolation of the product is simple because hydrazine is converted to gaseous nitrogen. 

Because a number of these organometallic compounds are commercially available, they are convenient starting materials for the preparation of certain aliphatic and aromatic diorgano tellurium dihalides. Tetraorgano tin and lead compounds transfer only two of their four organic groups to tellurium. Experiments with dialkyl-diaryl compounds showed that only the aryl groups are transferred. 

Diorgano tellurium dihalides were prepared in this manner from dialkyl, alkyl aryl, and diaryl tellurium compounds, and from tellurium heterocycles. However, 1-oxo-1,3-dihydro-2-benzotellurophene experienced ring cleavage when reacted with sulfuryl chloride7. 

When refluxed in an excess of a vicinal organic dibromide with or without a solvent, diaryl tellurium compounds produced diaryl tellurium dibromides in high yields1. The following dibromides effected these conversions 1,2-dibromoethane, 1,2-dibromocyclohexane, dibromocholesterol, and l,2-dibromo-2-phenylpropanoic acid1. Allyl bromide (but not butylbromide) transferred bromine to tellurium at 180 Diphenyl tellurium dihalides were observed as by-products when diphenyl tellurium was heated with iodoacetic acid or 1-bromopropanoic acid2. 

Dialkyl, diaryl, and alkyl aryl tellurium dihalides combine with 1,1 -dimethyl-3,5-dioxocyclohexane (dimedone) to form tellurium ylides9,10... 

Diorgano tellurium dichlorides and dibromides react with silver carboxylates " " or sodium carboxylates with formation of diorgano tellurium dicarboxylates. The same conversion was accomplished by shaking diaryl tellurium dichlorides with an Amberlite IR 45 resin in the carboxylate form or by treating bis[trifluoromethyl] tellurium dihalides with trifluoroacetic anhydride. ... 

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