Peterson alkenation carbonyl compounds

Trialkylsilyl groups have a modest stabilizing effect on adjacent carbanions (see Part A, Section 3.4.2). Reaction of the carbanions with carbonyl compounds gives (3-hydroxyalkylsilanes. (3-Hydroxyalkylsilanes are converted to alkenes by either acid or base.270 These eliminations provide the basis for a synthesis of alkenes. The reaction is sometimes called the Peterson reaction.211 For example, the Grignard reagent derived from chloromethyltrimethylsilane adds to an aldehyde or ketone and the intermediate can be converted to a terminal alkene by acid or base.272... 

A recent modification of the Peterson reaction involves the use of fluoride ion catalysts. Reaction of bis(trimethylsilyl)methyl derivatives 166 and carbonyl compounds gives the expected alkenes 167 (as shown in equation 137) in high yields, especially for non-enolisable carbonyl compounds, and in some cases with high stereoselectivity209. 

The Peterson reaction allows the preparation of alkenes from a-silylcarbanions and carbonyl compounds (ketones and aldehydes) via the intermediate (B-hydroxysilanes. Addition of the silylcarbanion to a carbonyl compound and subsequent aqueous work up produces diastereomeric P-hydroxysilanes, which maybe isolated. It is possible to prepare either cis-or frans-alkenes from the same p-hydroxysilanes intermediate (Scheme 4.39). 

Anions of a-silyl phosphonates of type (153) also undergo additions to carbonyl compounds. The corresponding addition products, 3-silyl alkoxides, can react with ketones to yield the product of the Peterson alkenation or the Wittig reaction. In practice only the Peterson product (154) is obtained, indicating that loss of OSiMes is faster than elimination of C PPhs (Scheme 68). 72 If the a-silyl carbanion is adjacent to a chlorine atom (155), an internal displacement reaction follows the initial formation of the -silyl alkoxide, and epoxides (156) are formed (Scheme 69). 74... 

The term Peterson alkenation has been used to describe the elimination of a functionalized organo-silicon compound with alkene formation for substrates synthesized by these methods. In accordance with the mechanistic definition outlined in the introduction to this cluq)ter, such topics are not considered in detail in this review. For the purpose of this discussion, the Peterson alkenation will be considered as the addition of an anion derivative to a carbonyl compound, followed by elimination to the alkene. 

In the original study by Peterson, the alkenation procedure was found to be compatible with sulfur and phosphorus substitution. The alkenation reaction has been tqrplied successfully to a variety of substituted alkenes. Because of the aiuon-stabilizing nature of the thiophenyl, the p-hydroxysiliuie is not isolated and the elimination to the alkene takes place directly to form a 1 1 mixture of ( )- and (Z)-isomers. Ager studied the reaction of the lithio anions of phenyl (trimethylsilyl)methyl sulfides (318) with a variety of carbonyl compounds (equation 72). Yields of this process were good, and addition occurred even with enolizable substrates. This reaction was extended to vinyl sulfones. In contrast to the sulfide case, the substituted sulfone silyl anion behaves as a base, leading to undesired enolization. The best yields were observed for the case where R is a hydrogen or phenyl. 

In the P-ketosilane approach, the condensation of a-silyl carbanions with carbonyl compounds produces mixtures of diastereomeric P-hydroxysilanes. Therefore, the preparation of stereodefined alkenes via the Peterson reaction hinges on the availability of just one diastereomer. To overcome this shortcoming, procedures have been developed to prepare stereoselectively P-hydroxyalkylsilanes via the P-ketosilane or the epoxysilane routes, as exemplilRed below. 

Peterson olefination Preparation of alkenes from a-silyl carbanions and carbonyl compounds. 344... 

Among the different methods for the synthesis of alkenes, none matches the versatility of carbonyl olefination.290 It has been extensively studied since the discovery of the Wittig reaction,291292 and a wide variety of approaches to transform carbonyl compounds into alkenes have been developed. Besides the classical Julia reaction,94 the most generally applicable methods for direct olefination of carbonyl compounds include the Wittig,291,293,294 Homer-Wittig,295,293,296 Homer-Wadsworth-Emmons,297,298,293 Peterson,299 301 Johnson,302 and Julia-Kocienski303,304 reactions. All of these methods involve the addition of a... 

Peterson aikenation of carbonyl compounds with trimethylsilylmethoxymethyl carbanion (14) can also give enol ethers. An example is the reaction of (14) with adamantanone. Another method of alkene synthesis is the elimination of CO2 and H2O from a P-hydroxycarboxylic acid. If the carboxylic acid is substituted by an a-alkoxy group, the reaction can be used for the synthesis of enol ethers, as illustrated in Scheme 4. ... 

Condensation of ot-silylalkyl compounds with carbonyl compounds to form alkenes has been known as the Peterson olefination reaction. Usually an a-silanyl carbanion generated in situ... 

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