Peterson reaction examples

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... 

One interesting example of pentacoordinate silicon is a 1,2-oxasiletanide, reported by Okazaki and coworkers61, which can be regarded as the intermediate of the Peterson reaction. Thus, treatment of a /1-hydroxysilane (28) with butyllithum afforded oxasiletanide... 

Carbonyl homologation. The reagent forms adducts with aldehydes and ketones, which do not undergo spontaneous elimination of (CH3)3SiOLi (Peterson reaction). However, the alcohols are converted into enol ethers on treatment with KH in THF at 0°, or into aldehydes when treated with 90% formic acid.1 Example ... 

A general approach to precursors of p-quinonemethides has been developed that involved the olefinations of p-quinoneketals as 615 with suitable nucleophiles. For example, the reaction of 615 with the anion derived from 613 led directly to the p-quinonemethide ketal 616 via a Peterson reaction (Scheme 57) (225). Alternatively, 616 was prepared by the initial reaction of 615 with the anion of 614 followed by mild dehydration of the intermediate tertiary alcohol... 

In addition to the examples in Table 1, the Peterson methylenation has been used in several interesting natural product syntheses, as the examples in equation (2)-(6) indicate. Danishefsky and coworkers used the Peterson reaction in an approach to mitomycins (4 equation 2). This tq>plication demonstrated the use of unique elimination conditions. The hydroxysilane intermediate was stable to direct Peterson elimination. Therefore, the removal of the silyl protecting group and the elimination of the silyloxy group were carried out with DDQ in quantitative yield. 

The a-silyl caibanions necessary to tqiply the Peterson reaction to higher substituted examples are limited by the ability to efficiently produce the anion. A clever example of an altenuitive to the Wittig reaction for ethylidene formation to give (285) with a-(trimethylsilyl)vinyllithium was utilized by Jung in the synthesis of coronafacic acid (Scheme 40). ... 

While these examples point to the possible use of the Wittig and the Peterson reactions as complementary methods for (Z)- and ( )-alkene formation in cases with conjugating fiinctiotuility, it must be emphasized that no systematic predictive rule can be rqrplied to the possible selectivity, and this area remains one of active research. 

Several groups have demonstrated that desilylation of dialkyl l-(trimethylsilyl)methylphosphonates initiated by means of fluoride ion (CsF, KF, or TBAF) is an effective process for the transfer of carbanions to electrophilic centers. Some examples involving the fluoride-induced formation of a-phosphonylated carbanions from dialkyl l-(trimethylsilyl)methylphosphonates containing a fragile C-Si bond have been described. Cleavage of the carbon-silicon bond under these conditions offers the advantages of neutral conditions and contributes to obtain better yields from sensitive substrates than those obtained under basic conditions. This procedure, which appears operationally simpler and cleaner than traditional protocols, has been applied to the preparation of alkenes " and 1-alkenylphosphonates" by Homer-Wadsworth-Emmons and Peterson reactions, respectively. 

PMB-protection of a P-hydroxysilane can be accomplished without competition from the Peterson elimination (Example 2), which would occur under the basic or acidic conditions required for many other alkylation reactions. 

Roush has provided a particularly noteworthy example showing the synthetic adaptability of stereorich cyclohexylsilane 73. Minimally protected dibenzyl pentaol 73 undergoes acid-mediated Peterson elimination to 74, base-mediated Peterson reaction to 76, and KFT oxidation to inositol derivative 75 (eq 18). ... 

Lithio-2-trimethylsilyl-l,3-dithiane is the most widely utilized reagent for the conversion of ketones and aldehydes to the corresponding ketene dithioacetals (Scheme 2.49) [126-128]. It is used for the synthesis of functionalized 2-alkylidene-1,3-dithianes 79 [129-135]. The 2-alkylidene-l,3-dithianes 79 thus synthesized are useful synthetic intermediates, which are conveniently accessible by means of Peterson reactions, and they can be transformed into various compounds [136, 137]. For example, compounds 79 are converted to the corresponding carboxylic acids, aldehydes, and enones by hydrolysis, hydrogenation followed by hydrolysis, and deprotonation followed by alkylation and hydrolysis, respectively (Scheme 2.49) [138-140]. 

Some examples of germanium versions of the Peterson reaction, such as syntheses of terminal alkenes, have been reported [383]. Peterson-type reactions of (trimeth-ylgermyl)acetate esters 235 with some aldehydes give the corresponding ( )-alkenes stereoselectively, whereas the use of the silyl analogues gives a mixture of the geometrical isomers (Scheme 2.145) [384, 385]. 

Chiral tridendate ligands have been utilized to effect asymmetric Peterson reactions, resulting in olefins with axial chirality in high yields and enantioselectivities. This is reported as the first example of its kind, namely the enantioselective Peterson olefmation of a-silanyl ester enolates 33 with substituted cyclohexanones 32, facilitated by an external chiral ligand 34. 

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