Diphenyl ditelluride (PhTeTePh) adds to a variety of acetylenes upon irradiation with visible light in the absence of solvent to provide vie-bis(phenyltelhtro)alkenes in good yiehis. The reaction may proceed by a radical-chain mechanism that includes the addition to acetylenes ofphenyltelbtro radical (PhTem) generated in situ by photolysis of diphenyl ditelluride. followed by the St,2 reaction between thus formed B-(phenyltelluro)alkenyl radicals and diphenyl ditelluride. In the cases of unactivated acetylenes such as 1 -octyne, the addition proceeds stereoselectively IO provide only (E)-vie-bis(phenyltelbtro)alkenes. Contrary to this, activated acetylenes like phenylacetylene give rise to a mixture of E-and Z-isomers of vicbis(phenyltelluro)alkenes. Since the obtained vie-bis(phenyltellwo)alkenes indicate absorption in the near-W. irradiation with near-W li@tt in solvent cautes a novel reverse reaction of the adducts to the starting acetylenes and diphenyl ditelluri&. Accordingly, irradiation with visible light (a4W nm) under high concentrations @the substrates induces the addition of (PhTe), to acetylenes, whereas irradiation with near-ultraviolet (>300 nm) under oUttion condition causes the reverse reaction.
in good yields (eq 1, Y = Te).13 This paper describes full details of this reaction.