Sp carbanions

Retro-Brook rearrangement of the [l,3]-variant will readily take place in sp and sp carbanion systems. Kuwajima and Takeda and Corey and Rticker have developed the [l,3]-retro-Brook rearrangement of silyl enol ether anions which provide a-silyl ketones (equation 100 and 101). 

Generation and Reactions of sp -Carbanionic Centers in the Vicinity of Heterocyclic Nitrogen Atoms... 

This review concentrates on the generation and subsequent reactions of two broad types of carbanion (i) ring ip--carbanions in azaheterocyclic systems, and (ii) external sp -carbanions of substituent groups adjacent to an aza-heterocycle. 

Dr. Gordon Rewcastle of the University of Auckland, New Zealand, and your Editor have covered the chemistry of sp -carbanions as generated in the vicinity of heterocyclic nitrogen atoms, a field that has expanded immensely in the last several years. 

Rewcastle, G. W., Katritzky, A. R., Generation and Reactions of sp -Carbanionic Centers in the Vicinity of Heterocyclic Nitrogen Atoms, 56, 155. 

The first example is a vinyl bromide and vinyl (sp ) carbanions are more stable than saturated (sp ) carbanions because of the greater s character in the C-Li a bond. The second example is saturated like BuLi but, unlike BuLi, it is a tertiary aUcyl bromide. The t-alkyl carbanion would be less stable than the primary BuLi and is not formed. 

The pJCt value for 2-CHz of 1,3-dithiane is 31.1, indicating that the sulfenyl group stabilizes the adjacent carbanion. Theoretical studies present convincing evidence for the unimportance of d-orbital participation in the acidification of C—H bonds a to sulfur atoms. Whether or not 3d-orbitals are included in Ae basis set, the preferred conformation of CH2 H is predicted to be that of an sp carbanion (2). The calculation, NMR studies and crystallography all support a tetrahedral structure for the a-lithiated sulfide. ... 

The synthesis of a-selenoalkyl metals reported above is not limited to those compounds which possess alkyl or aryl groups on an sp carbanionic center. For example, a-selenoalkyllithiums bearing a vinyl (Scheme 94), furfuryl (Scheme 95), silyl (Scheme 96), - methoxy (Scheme 97) or seleno moiety (Schemes 77 and 98) 7t have been obtained in alinost quantitative yield from the corresponding fimctionalized selenoacetals - or orthoesters and Bu Li. The Se-Li exchange is in all these cases, except that of tris(phenylseleno)methane, exclusively observed even with those compounds which possess a hydrogen susceptible to metallation. The 6,6-bis(phenylseleno)-p-lactam shown... 

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