A NEW GENERAL-METHOD FOR THE PREPARATION OF UNSYMMETRICAL TELLURONIUMSALTS

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)d iaryltelluronium tetrafluoroborates 3 in quantitative yield. When a si loxycyclopropane, 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 alkyny ldiaryltelluronium tetrafluoroborates as well as the unsymmetrically t riarylated telluronium salt were obtained in good yields. The Te-125 c hemical shifts of these compounds span over the range delta 645-755 pp m, which were in accordance with the onium nature of the tellurium cen ter. An X-ray structural analysis of 3a clearly showed that the centra l tellurium atom has a distorted-pyramidal structure with a weak coord inative interaction between the tellurium and carbonyl oxygen atoms. T he telluronium salt [Ph(2)TeCH(2)CH(2)C(=O)Bu-t](+)[BF4](-) easily tra nsferred its alkyl moiety to a sulfinate anion to form the correspondi ng alkyl phenyl sulfone and diphenyl telluride, while the base-promote d reaction of [Ph(2)TeCH(2)C(=O)Ph](+)[BF4](-) with benzaldehyde affor ded a chalcone and diphenyl telluroxide.