Allylic and Benzylic Carbanions Substituted by Heteroatoms

Abstract This review covers allylic and benzylic carbanions in which a heteroatom and the double bond may be part of a conjugated system. Propargylic and allenic systems are also included. The cation is an alkaline or alkaline‐earth element; transition metals are excluded. The chapter by Gilman and Morton in 1954 was restricted to lithium derivatives. Reviews covering part of the subject include those on organometallic compounds, on reagents for nucleophilic acylation, on olefin synthesis with P(O)‐activated reagents, on the formation and reactions of carbanions derived from allylic sulfoxides, dithianes, nitrosoamines, thioethers and ethers, selenium compounds, on base‐catalyzed isomerization, and on rearrangements of carbanions. Allylic and benzylic carbanions adjacent to the following heteroatoms have been described: boron, nitrogen, oxygen, silicon, phosphorus, sulfur, chlorine, selenium, bromine, tellurium. The basicity and structures of these anions are considered first. This discussion is followed by sections on methods of generation of carbanions, reactions occurring during preparation, decomposition, and rearrangements of carbanions, reactions with electrophiles, regioselectivity and stereochemical aspects of the reactions, transformations of the reaction products, and some applications of these carbanions in synthesis.