Carbanion chemistry

This chapter will begin with a brief overview of the development of carbanion chemistry followed by a section devoted to the structure and stability of carbanions. Methods of measuring carbon acidity and systematic trends in carbanion stability will be key elements in this chapter. Next, processes in which carbanions appear as transient, reactive intermediates will be presented and typical carbanion mechanisms will be outlined. Finally, some new developments in the field will be described. Although the synthetic utility of carbanions will be alluded to many times in this chapter, specific uses of carbanion-like reagents in synthesis will not be explored. This topic is exceptionally broad and well beyond the scope of this chapter. 

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Juaristi, and L. L. Nebenzahl, in Comprehensive Carbanion Chemistry, Part A, E. Buncel, and T. Durst, eds., Elsevier, New York, 1980, Chapter 7. 

D. J. Cram, Fundamentals of Carbanion Chemistry, Academic Press, New Yoilc, 1965. 

Koch, H F In Comprehensive Carbanion Chemistry, Buncel, E, Durst, T Eds, Elsevier Amsterdam, 1987, Part C, Chapter 6 Hudlicky, M Chemistry of Organofluorine Compounds 2nd Ed, Ellis Horwood Chichester, U K, 1976, Chapter 5... 

Review R. B. Bates. C. A. Ogle, Carbanion Chemistry, pp8-10. Springer, Berlin 1983. 

T. Durst, Techniques in Carbanion Chemistry in Comprehensive Carbanion Chemistry, E. Buncel, T. Durst. Eds.. Vol. 5B, Chapter 5. pp 239-303, Elsevier, Amsterdam 1984. 

See the discussion in Cram, D.J. Fundamentals of Carbanion Chemistry Academic Press NY, 1965, p. 85. 

For a monograph on very weak acids, see Reutov, O.A. Beletskaya, I.P. Butin, K.P. CH-Acids Pergamon NY, 1978. For other discussions, see Cram, D.J. Furulamentals of Carbanion Chemistry Academic Press NY, 1965, p. 1 Streitwieser Jr., A. Hammons,... 

In this chapter, decarboxylation of disubstituted malonic acid derivatives and application of the transketolases in organic syntheses are summarized. Although decarboxylation may be seen as a simple C-C bond breaking reaction, it can be regarded as a carbaniongenerating reaction. As the future directions of this field, expansion of some unique decarboxylation reactions is proposed. In relation of carbanion chemistry, promiscuity of enolase superfamily is discussed. 

A major advantage of the sequence presented here is that the aldehyde group is protected at the siloxycyclopropane stage, which allows convenient storage of this stable intermediate. Of equal importance is the valuable carbanion chemistry that can be carried out a to the ester function. Efficient substitution can be achieved by deprotonation with LDA and subsequent reaction with electrophiles.12-13-6 This process makes several a-substituted [1-formyl esters available. Other ring opening variants of siloxycyclopropanes - mostly as one-pot-procedures - are contained in Scheme I. They underscore the high versatility of these intermediates for the synthesis of valuable compounds.6 Chiral formyl esters (see Table, entries 2-5) are of special... 

A certain dualism is observable in carbonium ion-carbanion chemistry, a dualism rather like that of lines and points in projective geometry. The reader may recall that interchanging the words "line and "point in a theorem of projective geometry converts it into a statement that is also a theorem, sometimes the same one. For most carbonium ion reactions a corresponding carbanion reaction is known. The dualism can be used as a method for the invention of new, or at least unobserved, carbanion reactions. The carbanionic reaction corresponding to the carbonium ion rearrangement is of course the internal nucleophilic... 

Some important reactions of silyl anions are as follows and they have emerged on the basis of the carbanion chemistry. 

In this section we shall examine in detail the role of n—a interactions in carbanion chemistry. Carbanion stability as well as relative acidities of organic molecules are important probes of n—a interactions. 

Functionalization of these reactive anionic chain ends can be achieved by a variety of methods all based on the general concepts of carbanion chemistry. For example, reaction with C02 or succinnic anhydride leads to the carboxy terminated derivatives [10], while hydroxy-terminated polymers can be easily obtained by reaction with ethylene oxide (Scheme 3) [11]. In select functionalization reactions, such as alkylation with p-vinyl benzyl chloride, the nucleophilicity of the carbanionic species may be necessary and this can be achieved by reaction of the chain end with 1,1-diphenylethene followed by functionalization [12,13]. 

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