A new general method for the preparation of unsymmetrical telluronium salts

A new general approach to a variety of unsymmetrical telluronium salts has been developed. Treatment of diaryltellurinyl difluorides 1 with silyl enol ethers 2 in the presence of BF3 . OEt(2) gave (2-oxoalkyl)diaryltelluronium tetrafluoroborates 3 in quantitative yield. When a siloxycyclopropane, an allylsilane, a benzylstannane, an alkenylstannane, an alkynylsilane, or an arylstannane was used in place of compound 2, the corresponding 3-oxoalkyl-, allyl-, benzyl-, alkenyl-, and alkynyldiaryltelluronium tetrafluoroborates as well as the unsymmetrically triarylated telluronium salt were obtained in good yields. The Te-125 chemical shifts of these compounds span over the range delta 645-755 ppm, which were in accordance with the onium nature of the tellurium center. An X-ray structural analysis of 3a clearly showed that the central tellurium atom has a distorted-pyramidal structure with a weak coordinative interaction between the tellurium and carbonyl oxygen atoms. The telluronium salt [Ph(2)TeCH(2)CH(2)C(=O)Bu-t](+)[BF4](-) easily transferred its alkyl moiety to a sulfinate anion to form the corresponding alkyl phenyl sulfone and diphenyl telluride, while the base-promoted reaction of [Ph(2)TeCH(2)C(=O)Ph](+)[BF4](-) with benzaldehyde afforded a chalcone and diphenyl telluroxide.