Reaction of Tetraorganyltelluriums with Acetylenes

Tetraalkyltelluriums (R₄Te) react with arylacetylenes (ArCCH; Ar = Ph, p-MeOC₆H₄, p-FCeH₄) to afford alkylation products (ArHCCHR). The alkylation proceeds preferentially in net trans fashion to give a cis-1,2-disubstituted olefin as the major product along with the concomitant formation of a tellur ide (R₂Te) and an alkene originated from a substituent of R₄Te which plays as a hydrogen source. The reaction of dibutyldidecyltellurium (ⁿBu₂TeⁿDec₂) with phenylacetylene yields nearly statistical ratios of products, PhCHCHⁿBu (41%, E/Z = 10/90), PhCHCHⁿDec (35%, E/Z = 11/89), ⁿBu₂Te (20%), ⁿBuTeⁿDec (41%), and ⁿDec₂Te (18%), indicating a random transfer of primary alkyl substituents. On the contrary, ⁿBu₂TeⁱPr₂ reacts with phenylacetylene much faster than ⁿBu₄Te affording only PhCHCHⁱPr. Under similar conditions Ph₄Te does not react with phenylacetylene and ⁿDec₂TePh₂ decomposes quickly to ⁿDecTePh (95%), 1-decene (93%), and benzene (99%). The alkylation is proposed to proceed by the radical addition of R₄Te to ArCCH to yield (R₃Te) ArCCHR, which then decomposes to afford an olefin via a β-hydrogen transfer from R on tellurium to the vinyl carbon.