Tellurium-Wittig reactions

Tellurium-Wittig reactions.1 The reaction of aldehydes with a-bromo esters or ketones, triphenyl phosphite, and a weak base in the presence of a catalytic amount of Bu2Te results in ct, l-unsaturated esters and ketones. The function of the triphenyl phosphite is the regeneration of Bu2Te from the dibutyl telluroxide formed in the... 

Tellurium sources, 22-24 Thermodynamics in cyclo-oligomerization, 185-186 butadiene insertion, 187-188 reductive elimination, 193, 194 selectivity control, 212 polysilane isomerisation, 158-160 see also Stability Thermolysis, 135, 136, 158 THF (tetrahydrofuran), 97, 150, 153 Thio-Wittig reaction, 37 Tin, 121... 

Olefination and cyclopropanation. Preparation of alkenyl allyl ethers by the Wittig reaction is readily achieved. Tellurium and arsonium ylides tend to produce cyclopropyl ketones on reaction with enones. ... 

Kumar and Dittmer have reported the synthesis of intermediates for the lactone moiety of mevinic acids using tellurium-induced nucleophilic reduction developed by their own group as the key step [122] (Scheme 75). Alcohol 331 was protected and converted into aldehyde 332, which upon Wittig reaction and reduction gave allylic alcohol 333. Sharpless epoxidation of 333 and tosylation of the primary alcohol afforded tosylate 334, which underwent the tellurium-induced transposition providing lactone 335 through spontaneous lactonization. However, in the case of the corresponding fcrf-butyl ester, there was no spontaneous lactonization observed. 

Reactions of phosphines and phosphites have received some attention but their preparative value is limited. The zwitterion formed from diphenylmethylphosphine and benzyne rearranges to ylide (124) which can be captured by Wittig alkenation, with cyclohexanone, in about 20% yield.159 Some synthetically useful reactions of tellurium and selenium compounds with arynes have been reported. For example, heating diphenyl iodonium carboxylate and bis(p-ethoxyphenyl) ditelluride in dichlorobenzene affords the compound (125).160 The corresponding reactions with diphenyl selenide and diphenyl sulfide... 

The synthesis of tetraphenyltellurane (54) was first reported by Wittig and Fritz in 1952. 2 compound, easily prepared by the reaction of phenyllithium with tellurium tetrachloride, is a relatively stable substance which decomposes above 100°C to give diphenyltelluride (55) and biphenyl (5). Later, other tetraaryltelluranes have been prepared by the same method. 2... 

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