Alkyltelluro

As found by Engman et al. (1999), sodium alkyltelluroates are excellent reagents for the generation of aryl radicals from the corresponding iodides in the dark. Accordingly, l-(2-iodo-phenyl)-l-methyloxirane reacts with two equivalents of sodium 1-butyltelluroate giving 2,3-dihydro-3-hydroxy-3-methylbenzo[( ]tellurophene, which was isolated in 62% yield. The latter was readily converted into 2,3-dihydro-3-methylbenzo[( ]tellurophene on treatment with a catalytic amount of p-toluenesulfonic acid (94% yield Scheme 7.42). 

Phenyl(alkyltelluro)acetylenes (general procedure) n-BuLi (1.35 M in hexane, 22.2 mL, 30 mmol) is added dropwise to phenylacetylene (3.10 g, 30.0 mmol) in THF (15 mL) at 0°C nnder N2. After stirring for 5 min at 0°C, elemental Te (3.90 g, 30.0 mmol) is added and the mixtnre reflnxed nntil the Te disappears ( 30 min). The heat source is removed and the alkyl halide (30 mmol) is added. The mixtnre is stirred for 40 min at room temperatnre, then dilnted with ether (60 mL), washed with brine and the layers separated. The organic phase is dried (MgS04), evaporated and the residne purified by Si02 flash chromatography (elution with hexane). 

Another highlight of these additions was a systematic investigation of the use of alkylseleno- and alkyltelluro groups as non-transferable ligands of alkyl higher-order cyanocuprates [(RY)Cu(CN)R Li2, Y=Se, Te] in addition to enones. The following example is illustrative. 

Imaeda K, Enoki T, Shi Z, Wu P, Okada N, Yamochi H, Saito G, Inokuchi H (1987) Electrical conductivities of tetrakis(alkylthio)tetrathiafulvalene (TTCn-TTE) and tetrakis(alkyltelluro) tetrathiafuivaienes (TTeC -TTF). Bull Chem Soc Jpn 60 3143-3147... 

Tellurium-lithium exchange proceeds in much the same way as selenium-lithium exchange but is rarely used.144 Vinyltellurides such as 179 can be converted stereospecifically into vinyllithiums 180,145 and alkyltelluro-heterocycles have been used as precursors to lithio-species.146... 

Recently, substituted aromatic tellurides were submitted to the tellurium-lithium exchange reaction as a way to access substituted aryllithiums,48 synthetic intermediates normally prepared by halogen-lithium exchange. Alkyltelluro heterocycles were also successfully transformed into lithium heteroaromatics.246 247... 

V-Methylbenzamide and 2-bromobenzoic acid were similarly converted to the 2-alkyltelluro-substituted compounds1. 

The alkyltelluro group is generally introduced into aldehydes and ketones protected in the form of their acetals. The acetal groups in the protected acetylphenyl alkyl and 2-formylphenyl alkyl tellurium compounds are hydrolyzed by strong sulfuric or hydrochloric acid to carbonyl groups without affecting the C — Te — C moiety. 

Diethyl a)-(alkyltelluro)-l-alkylmalonates condensed with urea and thiourea to produce al kyltelluro-substituted barbiturates4. 

Alkylation of dilithium ethyneditellurolate with methyl iodide or ethyl iodide yielded bis[alkyltelluro]ethynes ... 

Alkyltelluro-substituted tetrathiafulvalenes were obtained as products of the reactions between lithium tetrathiafulvalenetellurolates and methyl iodide or ethyl iodide. ... 

Applications of Crown Ethers.—Crown ethers have been found to form molecular complexes with bromine that can be used as reagents in bromination reactions, e.g. of alkenes. The crown-halogen interaction seems not to be encapsulation but rather to be the formation of a polymeric structure. The complexes of nitro-nium tetrafluoroborate (NO2BF4) with various crown ethers, for example the 1 1 complex with 18-crown-6, have been reported to be selective nitrating agents. A new rapid synthesis of alkylseleno- and alkyltelluro-arenes from arenediazon-ium tetrafluoroborates and dialkyl diselenides or ditellurides employs KOAc and 18-crown-6 as a phase-transfer catalyst a radical mechanism has been suggested. Fluorine-19 n.m.r. evidence has been presented to show that KF forms... 

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