Desilylation electrophile-induced

Certain representative examples of electrophile-induced desilylation of lallylsilanes are given below. 

However, such exceptions are relatively rare. Some typical examples of electrophile-induced desilylation are given on p. 16. 

For aspects of electrophile induced ipso-desilylation, see (a) Mills,... 

Marino and his coworkers [20a], on the other hand, studied the fluoride ion-induced desilylation of ethyl 2-silyloxycyclopanecarboxylates 24 and the resulting "homoenolate" anion 25 was allowed to react with different electrophiles, such as Michael acceptors, to give dissonant cyclopentene rings (26) via a [3 -i- 2] annulation strategy (Scheme 5.16). 

In the rationale of Scheidt et al., a carbene catalyst (48) adds to the acylsilane 49 to produce - after 1,2-silyl migration - the intermediate 50 (Scheme 9.13). The alcohol is believed to induce a desilylation, leading to the Breslow-intermediate 26. Due to the reduced electrophilicity of the acylsilane (in comparison with an aldehyde), the conjugate addition predominates. 

Fluoride-induced desilylation-cyanation studies have been undertaken 138) with several electrophilic cyanogen type reagents. The best results were attained 138) when the 1-silyl-l-vinylcyclopropane shown in Scheme 65 was heated in a THF solution containing 4 equivalents of phenylcyanate. This reaction has been used 138> as a key step for the synthesis of ( )-hinesol and of (+)-P-vetivone (Scheme 65). 

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. 

Scheidt recently reported that a-silyl alkoxides generated from a-silyl silylethers 79 by fluoride-induced desilylation instead of deprotonation of a-silyl alcohol can be trapped by primary alkyl and by allylic and benzylic electrophiles via a Brook rearrangement (Scheme... 

Iwao et d. introduced an efficient methodology ftH the synthesis of 3,4-disubstituted indoles 113 (57). Their strategy comprises two sequential steps 1) selective functionalization of l-silyl-3-dimethylaminomethylindole (111) at the 4-position by directed lithiation, followed by quenching with electrophiles, for the preparation of 4-dimethylamino-substituted indole 112 (58) 2) substitution of the dimethylamino group of 112 for various nucleophiles giving 113 upon desilylation through quatemization followed by a fluoride ion-induced elimination-addition reaction (Scheme 17) (59). 

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