Generation of Carbanion

Stereochemical constraints in cyclic sulfones and sulfoxides impart increased weight to strain and conformational factors in the generation of carbanions and their stability, causing distinct differences between the behavior of cyclic and open-chain systems233, due primarily to the prevention of extensive rotation about the C —S bond, which is the major way that achiral carbanions racemize. Study of the a-H/D exchange rate fce and the racemization rate ka may provide information concerning the acidity-stereochemical relationships in optically active cyclic sulfone and sulfoxide systems. 

Michael addition has been employed as a key step in the formation of four-membered ring compounds.6 As outlined, indirect generation of carbanions from 3,3-dimethyl-4-tosyloxybut-... 

For the generation of carbanions, carbenes, etc., sodium hydroxide can be used as a base. Thus use of dangerous, expensive, and inconvenient reagents (t-BuOK, NaNH2, or NaH) is eliminated. Thanks to this, the use of large quantities of meticulously dried organic solvents is also avoided. 

Following methods are generally used for the generation of carbanions. 

The generation of carbanions and their reactions with aromatic aldehydes and ketones... 

The vast utilization of hindered secondary amines like diisopropylamine or dicyclohexylamine in carbanion chemistry is also based on the difference in their behavior toward protons and other electrophiles. Thus quite a number of the methods depend upon the use of the lithium or magnesium salts of these amines for the generation of carbanionic species. These salts are very strong kinetic bases and therefore are able to abstract a proton from a variety of C-H acids. At... 

For practical purposes, it would seem useful to have an overview of methods for the generation of carbanions and guidelines on compatibility with various polymers and linkers. In the following list, we summarize certain commonly used carbanions, linkers, supports, and methods of generation (Table 8). 

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