SYNTHESIS, X-RAY STRUCTURE, THERMAL-STABILITY AND REACTIONS OF TRIARYL(3-OXOALKYL)BISMUTHONIUM SALTS

Treatment of triarylbismuth difluorides 2 with siloxycyclopropanes 3 i n the presence of trimethylsilyl trifluoromethanesulfonate (triflate) or boron trifluoride-diethyl ether gave the corresponding triaryl(3-ox oalkyl)bismuthonium salts 4 as crystals, X-Ray crystallographic;analys is of the triflate 4a showed that the central bismuth atom has a disto rted tetrahedral geometry with weak intramolecular coordination by the oxygen atoms of the carbonyl group and triflate anion, Whilst all oni um salts 4 are thermally stable in a solid state, the triflate 4a slow ly decomposed in chloroform to give triphenylbismuthane 6 and an ester 7 quantitatively, In nucleophilic solvents such as MeOH, DMSO and DMF , both triflate 4a and tetrafluoroborate 4d underwent decomposition in a complicated way to afford the bismuthane 6, 3-methoxypropanoyl comp ounds 8a,b, alpha,beta-unsaturated carbonyl compounds 9a,b, diphenylbi smuth triflate 10a or tetrafluoroborate 10b and alkoxysulfonium salts 11a,b, The formate 12 was an additional product from 4d in DMF. The bi smuthonium salt 4d reacted with dimethyl sulfide 13 and sodium benzene sulfinate 15 to afford the sulfonium salt 14 and the sulfonyl ketone 1 6, respectively, Reaction of the salt 4d with potassium halides 17 in DMF gave the enone 9b, formate 12 and halogeno ketone 18 in varying yi elds depending on the nucleophilic nature of the halogen anions employ ed. When treated with KOBu(t), the salt 4d underwent facile beta-elimi nation to yield the enone 9b. In all of these reactions, the triphenyl bismuthane moiety behaved as a good leaving group.