Peterson olefinations

It is seldom appreciated that cyclopropanes are more reactive toward addition of acid than are olefins. Peterson 1 ), for example, showed that... 

Related reactions , Horner-Wadsworth-Emmons olefination - Still-Gennari modification, Julia-Lithgoe olefination, Peterson... 

Julia-Lithgoe olefination, Peterson olefination, Tebbe olefination, Wittig reaction, Wittig reaction - Schiosser modification ... 

Addition of a-silylcarbanions to ketones and subsequent elimination of a silanoale or silanol afford the corresponding olefins (Peterson reaction) (eq (33)) [30]. The use of a-silylcarbanions in olefination of carbonyl compounds offers some advantages over the Wittig reaction that the method can be applied to highly enolizable ketones and both cis and trans isomers are stereoselectively formed depending on the reaction conditions employed for the elimination step (eq (34)) [31]. 

Silicon-stabilized anions can be put to various uses, among which is the formation of olefins (Peterson reaction), and the 1-phenylthio-l-trimethylsilyl-alkanes required as precursors can also be used in a synthesis of aldehydes. Some of the chemistry reported this year relating to such compounds is shown in Schemes 20 and 21. ... 

Peterson Olefination review . Synthesis 1984, 384 Organic Reactions 1990, 38 1. 

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 ... 

The following acid-catalyzed cyclizations leading to steroid hormone precursors exemplify some important facts an acetylenic bond is less nucleophilic than an olelinic bond acetylenic bonds tend to form cyclopentane rather than cyclohexane derivatives, if there is a choice in proton-catalyzed olefin cyclizations the thermodynamically most stable Irons connection of cyclohexane rings is obtained selectively electroneutral nucleophilic agents such as ethylene carbonate can be used to terminate the cationic cyclization process forming stable enol derivatives which can be hydrolyzed to carbonyl compounds without this nucleophile and with trifluoroacetic acid the corresponding enol ester may be obtained (M.B. Gravestock, 1978, A,B P.E. Peterson, 1969). 

Synthesis of olefins by stereospecific rerbctfve elimination of S-hydroxyaikyl selenides (a variant at Peterson olefinatlon) by means of MeSOjCI. HCIO4 or P2I4. 

Lastly, a-trimetfayisflyl enolates have been added to trifluoromethyl ketones to effect Peterson olefination of the tnfluoromethyl ketones [IS (equation 13)... 

The Peterson olefination can be viewed as a silicon variant of the Wittig reaction, the well-known method for the formation of carbon-carbon double bonds. A ketone or aldehyde 1 can react with an a-silyl organometallic compound 2—e.g. with M = Li or Mg—to yield an alkene 3. 

The Peterson olefination is a quite modern method in organic synthesis its mechanism is still not completely understood. " The a-silyl organometallic reagent 2 reacts with the carbonyl substrate 1 by formation of a carbon-carbon single bond to give the diastereomeric alkoxides 4a and 4b upon hydrolysis the latter are converted into /3-hydroxysilanes 5a and 5b ... 

The next step of the Peterson olefination allows for the control of the E Z-ratio of the alkene to be formed by proper choice of the reaction conditions. Treatment of /3-hydroxysilanes 5 with a base such as sodium hydride or potassium hydride leads to preferential -elimination to give alkene 3a as major... 

The above mechanism involves a-opening of the epoxysilane, followed by a 1,2-elimination of a /3-hydroxysilanc (Peterson olefination, Chapter 10). However, it has recently been shown that aj8-dihydroxysilanes, particularly t-butyldimethylsilyl species, undergo an acid-catalysed sila-pinacol rearrangement to produce /J-aldehydo- and /i-kctosilancs (5) ... 

The main utility of Peterson olefination lies in the contrasting stereochemical requirements (6) for elimination, use of base requiring a syn conformation whereas acid conditions demand an anti conformation, with complementary geometrical results ... 

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