Reactions of tetraorganyl tellurium with acetylenes

TetralkylteUnriiims, prepared in situ by the reaction of tellurium tetrachloride with 4 equiv of alkyllithiums, react with arylacetylenes to afford dialkyl tellurides A, alkylation products B, an alkene C and minor amounts of a vinyl telluride D.  

The alkylation is rationalized as involving the radical addition of RaTc to the acetylene and the decomposition of the formed adduct to afford the dialkyltelluride and the olefin, originated from the displaced alkyl moiety via transfer of a hydrogen to vinyl cation. 

The alkylation proceeds mainly via a trans-mode giving cA-l,2-disubstituted adducts. When an excess of phenylacetylene is used, the yield of the alkylation product is raised (98%, EIZ=9 9l), indicating that the alkylation competes with the self-degradation of n-Bu4Te (to n-Bu2Te, butane and octane). 

An electron-donating (MeO) or an electron-withdrawing (E) substituent linked to the benzene ring is without effect in the reaction. 

Reaction ofn-Bu4Te with phenylacetylene (typical procedure for the reaction ofRfTe with acetylenes). To a stirred suspension of TeCl4 (323 mg, 1.2 mmol) in 6 mL of Et20 at 0°C was added n-BuLi (4.8 mmol, 3.1 mL, 1.58 M in hexane) dropwise. The suspension turned brown initially and then yellowish orange as the addition came to completion. The mixture was stirred for 0.5 h at 0°C and phenylacetylene (123 mg, 1.2 mmol) was added to it. The mixture was then warmed to room temperature and stirred until no more increase of B (1-phenyl hexene) was observed by GC (8 h). GC analysis of the mixture using dodecane as an internal standard showed that n-Bu2Te, B and D were formed in 93%, 62% E Z= 8 92) and 4% (ElZ = 50 50) yields, respectively. The reaction mixture was then poured into water 

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