Fluoride-ion mediated desilylative alkylations

Because of the available pentacoordinate state for silicon, fluoride ion and neutral fluorine in C—F bonds coordinate much more strongly to tetravalent silicon than to carbon, in spite of the comparable bond strengths of Si—F and C—F (132 kcal/mol). Therefore, most of the fluoride-ion-mediated reactions proceed via high valent silicate intermediates. The synthetic potential of the fluoride-ion-mediated reactions has been exploited in a number 

Aldol reaction and alkylation of ketones at the a-position via enol silyl ethers (11) under neutral conditions are good examples [8]. Ortho-quinodimethane (15) is afforded at room temperature and undergoes [4 + 2] cycloaddition [10]. In contrast, the thermal ring opening of benzocyclobutane requires a much higher temperature (180-190°C) [11]. The fluorine-mediated Si—C activation protocol was the preferred method for the formation of tetrafluoro-para-quinodimethane (19), which then dimerizes to octafluoro-para-cyclophane (20) [12]. Azomethine ylide (22) can be generated from 21 byAgF catalysis and is used for heterocycles syntheses [13]. 

The oxidative transformation of alkylsilanes bearing an alkoxyl group as a substituent on silicon to alkanols (Tamao oxidation) has often been employed in the syntheses of natural products because of the mild reaction conditions and retention of configuration (generally, Tamao oxidation requires at least one alkoxy or electron-withdrawing heteroatom group on the central silicon atom, but no alkoxy substituents are needed for the oxidative Si—C 

Palladium-catalyzed cross couplings of organofluorosilanes with vinyl [37] and aryl [38] halides and triflates are known, where the activation of the Si—C bond by fluoride ion plays an essential role in the coupling. The pentacoordinated fluoroorganic silanes promote the transmetallation to the aryl halide-palladium complexes strongly. At least one fluorine 

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