Peterson Reactions

Mechanism The Peterson alkenation offers the synthesis of desired alkene stereoisomer by careful separation of the two diastereomeric intermediate P-hydroxysilanes and subsequently performing elimination under two different conditions. 

The base-catalyzed elimination may proceed via a 1,3-shift of the silyl group after deprotonation or with the formation of a pentacoordinate 1,2-oxasiletanide that subsequently undergoes cycloreversion. 

The order of reactivity of alkoxides - K Na Mg - is consistent with the higher electron density on oxygen, hence increasing the alkoxide nucleophilicity. When the a-silylcarbanion contains electron-withdrawing substituents, the Peterson alkenation directly forms the alkene, without the isolation of (3-hydroxysilane. 

Recently, germyl, stannyl and plumbyl Peterson reactions have also been reported which demonstrate the vibrant development of this methodology. 

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The phosphorus ylides of the Wittig reaction can be replaced by trimethylsilylmethyl-carbanions (Peterson reaction). These silylated carbanions add to carbonyl groups and can easily be eliminated with base to give olefins. The only by-products are volatile silanols. They are more easily removed than the phosphine oxides or phosphates of the more conventional Wittig or Homer reactions (D.J. Peterson, 1968). 

The Peterson reaction has two more advantages over the Wittig reaction 1. it is sometimes less vulnerable to sterical hindrance, and 2. groups, which are susceptible to nucleophilic substitution, are not attacked by silylated carbanions. The introduction of a methylene group into a sterically hindered ketone (R.K. Boeckman, Jr., 1973) and the syntheses of olefins with sulfur, selenium, silicon, or tin substituents (D. Seebach, 1973 B.T. Grdbel, 1974, 1977) illustrate useful applications. The reaction is, however, more limited and time consuming than the Wittig reaction, since metallated silicon derivatives are difficult to synthesize and their reactions are rarely stereoselective (T.H. Chan, 1974 ... 

For the purpose of stereoselective synthesis the selective elimination at the stage of the /3-hydroxysilane 5 is not a problem the diastereoselective preparation of the desired /3-hydroxysilane however is generally not possible. This drawback can be circumvented by application of alternative reactions to prepare the /3-hydroxysilane 2 however these methods do not fall into the category of the Peterson reaction. 

Perseleninic acids, as oxidizing agents 240 Persulphenates 709 Persulphoxides 709 Perturbation 1050 Peterson reaction 332 Phase transfer catalysis 573-575, 985, 986, 990... 

Another method that has been used to prepare phosphaalkenes is the phos-pha-Peterson reaction, a phosphorus analog of the Peterson olefination [46-49]. In this reaction a lithium silylphosphide is treated with an aldehyde or ketone to yield the phosphaalkene (9). Analogous reactions can be conducted with bis(trimethylsilyl)phosphines (10) and ketones (11) using a catalytic quantity of anhydrous base (i.e., NaOH, KOH) [50]. Generally, the reactions proceed cleanly and in high yield. Sufficiently bulky substituents must be employed to stabilize the P=C bond and prevent rapid dimerization to 1,3-diphosphetaines. 

Base-catalyzed, Add-catalyzed and Thermal Eliminations of Trimethylsilanol. Peterson Reactions... 

Because of the large number of publications in this field, this chapter wiU be limited to giving an idea of developments in this area. Because the Peterson reaction can be viewed as a special case of base-catalyzed reaction, this reaction will be discussed in Section 10.2 after general base-catalyzed eliminations of trimethylsilanol... 

Because the mechanisms of the Peterson reaction, a synthetic alternative to the Wittig reaction, have recently been reviewed [13, 14], this section will try only to summarize recent developments and trends concerning the Peterson reaction. 

The Peterson reactions of amides of bis(trimethylsilyl)methylamines such as 1620 with TBAF in THE afford HMDSO 7 and the 1,2-dihydroisoquinolines 1621... 

This section deals with reactions that correspond to Pathway C, defined earlier (p. 64), that lead to formation of alkenes. The reactions discussed include those of phosphorus-stabilized nucleophiles (Wittig and related reactions), a a-silyl (Peterson reaction) and a-sulfonyl (Julia olefination) with aldehydes and ketones. These important rections can be used to convert a carbonyl group to an alkene by reaction with a carbon nucleophile. In each case, the addition step is followed by an elimination. 

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... 

Several variations of the Peterson reaction have been developed for synthesis of alkenylsilanes.80 -P-Arylvinylsilanes can be obtained by dehydration of (3-silyloxy alkoxides formed by addition of lithiomethyl trimethylsilane to aromatic aldehydes. Specific Lewis acids have been found to be advantageous for the elimination step.81... 

The Peterson olefination reaction involves the addition of an a-silyl substituted anion to an aldehyde or a ketone followed by the elimination of silylcarbinol either under acidic (awP -elimination) or basic (syn-elimination) conditions to furnish olefins178. Thus, Peterson olefination, just like Wittig and related reactions, is a method for regioselective conversion of a carbonyl compound to an olefin. Dienes and polyenes can be generated when the Peterson reaction is conducted using either an ,/l-unsaturated carbonyl compound or unsaturated silyl derivatives as reaction partners (Table 20)179. 

TABLE 20. Dienes and polyenes through the Peterson reaction... 

The spirocompounds 34 (M = Ti or Zr) have been prepared . Studies of the thermolysis of pentacoordinate 1,2-oxasiletanides 35, potential intermediates in both the Peterson reaction and the homo-Brook rearrangement of p-hydroxyalkylsilanes with bases, in the presence of a proton source afforded the olefin, RCH=C(CF3)2 and/or the alcohol, (CF3)2CHOH <99CL1139>. 

Formox [Formaldehyde by oxidation] A process for oxidizing methanol to formaldehyde, using a ferric molybdate catalyst. Based on the Adkins-Peterson reaction, developed by Reichold Chemicals, and licensed by that company and Perstorp, Sweden. Acquired by Dyno Industries in 1989. The process uses formaldehyde produced in this way to make formaldehyde-urea resin continuously. A plant using this process was to be built in Ghent by 1991, owned jointly by Dyno and AHB-Chemie. Licensed to 35 sites worldwide. Several other companies operate similar processes. 

One of the earliest synthetic uses of organosilicon reagents was the silicon equivalent of writing reaction called Peterson Reaction. 

The Peterson reaction utilizes a metal derivative of chloromethyltrimethylsilane and the yields are better than the Wittig reaction. The intermediate P-hydroxysilanes can undergo either cis or trans elimination depending on reagent choice. 

Huie, R. E., and N. C. Peterson, Reaction of Sulfur(IV) with Transition-Metal Ions in Aqueous Solutions, Adi Environ. Sci. Technol., 12, 117-146 (1983). 

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