Organic chemistry created by bismuth: Syntheses and applications

The syntheses and reactions of bismuthonium salts and bismuth ylides are re ported. Various types of bismuthonium salts bearing a Bi-C-sp3, Bi-C-sp2, o r Bi-C-sp bond have been prepared by the Lewis-acid promoted reaction of tr iphenylbismuth difluoride with organometallic reagents. The bismuthonium sa lts thus obtained behave as alkyl cation equivalents, alkenyl cation equiva lents, and carbene precursors. The bismuth ylides bearing a carbonyl group at the ylidic carbon react with carbonyl compounds to undergo epoxidation, transposition, or ring expansion depending on the structure of the substrat es employed. These reaction modes are characteristic of bismuth among the g roup 15 elements. The stabilized bismuth ylides bearing a highly cross-conj ugated ylidic carbon decompose, at an elevated temperature or in the presen ce of a copper catalyst, to give trisubstituted oxazoles. The observed uniq ue reactivities of the bismuthonium salts and the bismuth ylides are ascrib ed to the good leaving ability of the triarylbismuthonio group.