Alkyl phenyl telluroxides

When the reactions of benzenetellurinyl acetate or trifluoroacetate to olefins were carried out with nitriles as solvents and boron trifluoride diethyl etherate as catalyst, 2-acylamino-1-alkyl phenyl telluroxides were obtained. Telluroxide elimination produces 4,5-dihydrooxazoles2. 

Alkyl phenyl telluroxides and cycloalkyl phenyl telluroxides, with the exception of cyclohexyl derivatives, are unstable compounds, suffering the elimination reaction at room temperature. In contrast, n-alkyl phenyl telluroxides and cyclohexyl phenyl telluroxide are stable compounds and undergo elimination only by prolonged heating in toluene or THF, or by pyrolysis at 200-240°C. 

Finally, alkyl phenyl tellurones (prepared by oxidation of telluroxides with Nal04 are susceptible to similar conversions (method D). 

General procedure for telluroxide elimination by oxidation of alkyl phenyl tellurides in the presence of base. To a two-necked, round-bottomed flask (25 mL) containing alkyl phenyl telluride (1 mmol), triethylamine (1-2 mmol) and diethyl ether (5 mL) was added solid MCPBA (purity 80%) (2 mmol as pure MCPBA) portionwise at 25°C. The mixture was stirred with a magnetic stirrer for 2 h at the same temperature before being poured into... 

The reaction of alkyl phenyl tellurides with excess chloramine-T (A -chloro-A -sodium-p-tolysulphonamide) in refluxing THF leads to olefins, presumably through a tellurosul-phimino intermediate. Owing to the high yields obtained, this method seems to be highly competitive with the telluroxide elimination. 

Similar reactions with O-ethyl carbamate and terminal olefins yielded mixtures of 2-(ethoxycarbonylamino)-l-alkyl (Markovnikov adduct) and l-(ethoxycarbonylamino)-2-alkyl (anti-Markovnikov adduct) phenyl telluroxides that were again isolated as the corresponding diorgano tellurium compounds3. 

Treatment of sec-alkyl phenyl telluriums with 3-chloroperoxybenzoic acid in diethyl ether gave olefins in good yields. The reactions, which are postulated to proceed via a telluroxide intermediate, convert the alkyl halides used in the preparation of the alkyl phenyl telluriums to olefins1. 

As in the selenium case (Scheme 17) the oxidation of alkyl phenyl telluride with excess MCPBA in the presence of alcohols results in a facile substitution of a PhTe moiety by an alkoxy group. The reaction is assumed to proceed via a similar tellurone-MCPBA adduct intermediate. Oxidation of cycloalkyl telluride (61) was accompanied by ring contraction to produce an acetal (62), < while the bromination-hydrolysis method affords the allylic ether by telluroxide elimination (Scheme 22). ... 

The telluroxides were not purified. They were reduced by hydrazine hydrate to alkyl phenyl telluriums (page 433). 

Telluroxide elimination, Alkyl phenyl tellurides on oxidation with CIC6H4CO3H in ether afford alkenes as the major product. In some cases a stable Te(IV) compound is formed, which undergoes elimination on pyrolysis. Examples ... 

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