The Vinyl Carbanion¹

Reductive Elimination of Chlorinated Ethylenes by Zero-Valent Metals

“…Such isomerization has previously been shown to be negligible for -:CCldCHCl carbanions (49). A characteristic of such reactions is that elimination of trans substituents is much more favorable than is cis elimination.…”

“…For example, the hydrogen of TCE can be exchanged with that of water (48,61). Although the deprotonation step in dehydrohalogenation is slow, Miller and Lee (49) found that the free vinyl carbanion resulting from cis-1,2-dibromoethylene-d 2 deprotonation underwent reprotonation ∼25 times more rapidly than elimination. Although the deprotonation step in dehydrohalogenation is slow, Miller and Lee (49) found that the free vinyl carbanion resulting from cis-1,2-dibromoethylene-d 2 deprotonation underwent reprotonation ∼25 times more rapidly than elimination.…”

IntramolecularAnti‐Carbolithiation of Alkynes: Stereo‐Directing Effect of Lithium‐Coordinating Substituents

“…Products 4 are stereoisomerically pure and their NOESY spectra are consistent with formal anti ‐addition products (see Supporting Information). In comparison to aryl‐ or trimethylsilyl‐substituted alkenyllithiums, alkyl‐substituted ones are known to be configurationally stable [29–33] . As a consequence, the exclusive formation of anti ‐addition product 4 a from alkyl‐substituted alkyne 2 a suggests an anti ‐carbolithiation pathway.…”

“…In comparison to aryl-or trimethylsilyl-substituted alkenyllithiums, alkyl-substituted ones are known to be configurationally stable. [29][30][31][32][33] As a consequence, the exclusive formation of antiaddition product 4 a from alkyl-substituted alkyne 2 a suggests an anti-carbolithiation pathway. We postulate that this stereocontrol could originate from a MeOÀ Li interaction during the transition state and this rationale was subsequently supported by the computational studies (see below).…”

Reaction pathways in the gas phase negative ion chemistry of chlorinated ethenes

“…In solution, the base initiated elimination of HCl from Z-CHCl2CHCl has been reported to be more than 103 times faster than from E-CHCl2CHCl. 54 The reactions of the Ñuoroethenes with a number of alkoxide bases (B~) have been investigated by ion cyclotron resonance. 33…”