Organic Chemistry Created by Bismuth: Syntheses and Applications

The syntheses and reactions of bismuthonium salts and bismuth ylides are reported. Various types of bismuthonium salts bearing a Bi-Csp3, Bi-Csp2, or Bi-Csp bond have been prepared by the Lewis-acid promoted reaction of triphenylbismuth difluoride with organometallic reagents. The bismuthonium salts thus obtained behave as alkyl cation equivalents, alkenyl cation equivalents, 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 substrates employed. These reaction modes are characteristic of bismuth among the group 15 elements. The stabilized bismuth ylides bearing a highly cross-conjugated ylidic carbon decompose, at an elevated temperature or in the presence of a copper catalyst, to give trisubstituted oxazoles. The observed unique reactivities of the bismuthonium salts and the bismuth ylides are ascribed to the good leaving ability of the triarylbismuthonio group.