PHOTOINDUCED DITELLURATION OF ACETYLENES WITH DIPHENYL DITELLURIDE

Diphenyl ditelluride (PhTeTePh) adds to a variety of acetylenes upon irradiation with visible light in the absence of solvent to provide vic-bis(phenyltelluro)alkenes in good yields. The reaction may proceed by a radical-chain mechanism that includes the addition to acetylenes of phenyltelluro radical (PhTe) generated in situ by photolysis of diphenyl ditelluride, followed by the S(H)2 reaction between thus formed beta-(phenyltelluro)alkenyl radicals and diphenyl ditelluride. In the cases of unactivated acetylenes such as 1-octyne, the addition proceeds stereoselectively to provide only (E)-vic-bis(phenyltelluro)alkenes. Contrary to this, activated acetylenes like phenylacetylene give rise to a mixture of E- and Z-isomers of vic-bis(phenyltelluro)alkenes. Since the obtained vic-bis(phenyltelluro)alkenes indicate absorption in the near-UV, irradiation with near-UV light in solvent causes a novel reverse reaction of the adducts to the starting acetylenes and diphenyl ditelluride. Accordingly, irradiation with visible light (>400 nm) under high concentrations of the substrates induces the addition of (PhTe), to acetylenes, whereas irradiation with near-ultraviolet (>300 nm) under dilution condition causes the reverse reaction.