Peterson-type elimination

A useful application of the silver-mediated additions is 1,3 -diene synthesis by three-carbon elongation of aldehydes [48,51,53]. The bimetallic reagent 3-trimethylsilyl-l-propenylzirco-nocene chloride (A Scheme 8.23) reacts with aldehydes under the influence of a catalytic amount of Ag+ to give the intermediate zirconocene-alkoxide B, which then undergoes a Peterson-type 1,4-elimination of TMS alkoxide to stereoselectively afford ( )-dienes (fc/Z > 96 4) (Scheme 8.23). A Wittig reaction yields the same products without stereoselectivity (ca. 1 1 mixtures of E- and Z-isomers). 

Selenoaldehydes,2 In the presence of 5-10 mole% of butyllithium, this disilyl selenide converts aldehydes into selenoaldehydes with formation of the disiloxane [(CH,)3SiOSi(CH3),]. The active reagent is presumed to be lithium trimethylsilyl-selenide, (CH3)3SiSeLi, which can be regenerated by a Peterson-type elimination (equation I). 

AllyIsilanes are exceptionally versatile compounds with a well-established function in organic synthesis.3 General methods for their preparation, then, are valuable. The method described here is effective for elaboration of esters to allylsilanes. The transformation is conceptually straightforward twofold addition of a trimethylsilylmethyl metal species to the ester, followed by Peterson-type elimination from the resultant bis(trimethylsilylmethyi)carbinol, leads to the allylsilanes. 

Reaction of adamantanone with (Me3Si)3SiLi in hexane leads, via a Peterson-type elimination, to the silene, which dimerizes spontaneously to 1,2-disilacyclobutane in 85% yield [Eq. (51)] (98a,b)-... 

The rearrangement regularly takes place with retention of configuration at the carbon atom to which the silyl group is attached, and it is compatible with ketone and ester groups. In the case of p-hydroxy-silanes, no Peterson-type elimination occurs. Some representative reactions are shown in Scheme 31. 

Elimination of silyl groups with p-oxy groups, i.e., Peterson-type elimination, is a useful method for preparing stereodefined alkenes [101,102]. The synthetically useful allylsilanes are effectively synthesized in geometrically and enantio-merically pure forms through the Peterson-type elimination of organosilanes prepared by palladium-catalyzed bis-silylation (Eq. 57) [72, 73]. The intramolecular bis-silylation of optically active allylic alcohols in refluxing toluene af-... 

Suginome and Ito have developed a reliable method for the synthesis of highly enantioenriched allyl- and allenylsilanes. The synthetic process involves 1,3-chirality transfer from homochiral allyl and propargyl alcohols through Pd-catalyzed intramolecular bis-silylation and subsequent Peterson-type elimination (Scheme 10.142) [395]. This method provides an efficient route to enantioenriched allylsilanes bearing a hydroxyalkyl group, which are very valuable as synthetic intermediates for diastereo- and enantioselective synthesis of heterocycies and carbocycles [396]. Polymer-supported highly enantioenriched allylsilanes have been prepared from enantioenriched allyl alcohols and a polymer-supported disilanyl chloride [397]. 

The combination of the Pd-catalyzed bis-silylation and subsequent Peterson-type elimination was applied to the synthesis of aUenylsilanes from propargylic ethers. Scheme 7 shows a preparation of optically active aUenylsilane and its use in the synthesis of syn-homopropargylic alcohol. Use of the palladium-isonitrile catalyst is crucial to promote the bis-silylation effectively. 

Scheme 2.96. Fluoride ion induced Peterson-type elimination of -silyl-y-lactones.

The intermediate formed upon addition of an organolithium onto the carbonyl group of the heterocyclic starting material collapses by Peterson-type elimination of lithium trimethylsilanolate (Scheme 1-163). ... 

A novel intramolecular bis-silylation of propargylic disilanyl ethers followed by a Peterson-type syn elimination provides access to a variety of allenylsilanes (Table 9.36) [57]. The elimination is initiated by treatment of the presumed four-membered siloxane intermediate with BuLi. This intermediate could not be isolated, but spectral data were in accord with the assigned structure. The cycloaddition and elimination steps were shown to take place stereospecifically (Eq. 9.48). 

Addition of dimethylsulfonium methylide (122) to various Michael acceptors (121), followed by alkylation, has been reported to produce functionalized 1-substituted alkenes (124), arising via the unprecedented elimination (123), rather than the usual cyclopropanation products. In silyl substituted substrates, where a facile Peterson-type olefination is possible from the adduct, elimination took place instead. Aryl-substituted Michael acceptors (121 R1 = Ar) underwent a similar olefination to give 1-substituted styrene derivatives with moderate yields along with a side product, which arose by nucleophilic demethylation from the adduct of dimethylsulfonium methylide and arylidene malonates. Hammett studies revealed that selectivity for olefination versus demethylation increases as the aryl substituent becomes more electron deficient.164... 

Reaction of DMSB with triphenylsilyl-substituted oxiranyllithium leads to the formation of an olefinic silanol via sequential (1) coordination to the silicon, (2) Si-C bond migration, and (3) Peterson-type Si-O elimination to furnish the alkene. A pentacoordinate siliconate intermediate is presumably involved in this transformation. Therefore, it was reasonable to expect that addition of a nucleophile (methyllithium or lithium t>-propoxide) to an oxiranyl-substi-tuted SCB, which could generate a similar intermediate, would induce the C-Si bond migration to form the same silacyclopentane. Indeed, this alternative order of addition sequence provides the corresponding silanol with better efficiency (84% yield vs. 44%, Scheme 36). 

Anionic pentacoordinated 1,2-oxagermetanide was synthesized quantitatively by deprotonation of the corresponding -hydroxygermane (Scheme 10)63. Upon heating at 150 °C for 30 days, this compound equilibrated with another diastereoisomer and underwent a Peterson-type reaction with elimination of olefins (Scheme 10). 

DeShong (Scheme 20). Thus, reaction of nitrones with vinyl silanes followed by reduction provides Peterson - type intermediates which can then be eliminated to either Z- or E-products. Homoallylic amines were also prepared using allylsilane in the initial cycloaddition. Substitution reactions of allylic nitro compounds have received considerable attention and some examples are outlined in Scheme 21. In each case, examination of the regiochemistry of the reaction was of paramount concern, the results using palladium being superior to the SnCl mediated process. Allylic sulphides constitute yet another group of... 

Fluoride Ion Catalyzed Peterson-Type Reactions with Elimination of Trimethylsilanol... 

EWG = COgEt, CH=NBu, C(Me)=NBu R = Ph, PhCH=CH, 2-furyl, C7H15 Scheme 2.109. Fluoride ion catalyzed Peterson-type reaction with elimination of trimethylsilanol. 

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