Silanes fluoride induced reactions

Allylic transposition is observed in fluoride-induced reactions of allyl(trifluoro)silanes50 and allyl(trichloro)- and allyl(trialkoxy)silanes in the presence of hydroxylic promoters, e.g., 1,2-benzenediol51,52. Pentacoordinated silicates are believed to be involved53. 

In contrast, ( )- and (Z)-2-butcnyl(trifluoro)silanes undergo stereoselective fluoride-induced reactions with aldehydes to give anti- and. sy -products, respectively37. 

Fluoride-induced /S-elimination reactions of silanes having leaving groups in the position are important processes in synthetic chemistry, as, for, example in the removal of / -trimethylsilylethoxy groups. 

Analogous to its reaction with carbonyl compounds (see 6.3.4), benzyltrimethyl-silane undergoes a fluoride-induced nucleophilic substitution reaction on pyridine-1-oxides and quinoline-l-oxide to form 2-benzylpyridines (>70%) and 2-benzyl-quinoline (65%), respectively [57], Allyltrimethylsilane reacts with pyridine-l-oxide to produce 2-propenylpyridine (56%). 

Reaction of allylic silanes with aldehydes and ketones can also be induced by fluoride ion, which is usually supplied by the THF-soluble salt tetrabutylammonium fluoride (TBAF). Fluoride adds at silicon to form a hypervalent anion with much enhanced nucleophilicity.73 An alternative reagent to TBAF is tetrabutylammonium triphenyldi-fluorosilicate.74... 

An alternative rearrangement pathway may be observed when the silicon atom bears aryl substituents or when simple aUcanoyl triaUcylsilanes are used. This pathway is similar to one suggested, but not observed, by Brook for reaction of acyl silanes with aikoxide Addition of fluoride ion to silicon induces a migration to the carbonyl car-... 

Nitrogen Silylation Reactions. lV-(Trimethylsilyl)imidazole can serve as an electrophilic trap for the highly reactive intermediate formed in the reaction of A -aryl imines with trifluo-romethyltrimethylsilane under fluoride catalysis (eq 15). In the absence of lV-(trimethylsilyl)imidazole, the reactive intermediate decomposes to difluorocarbene, shifting the equilibrium toward the starting imine derivative. Chlorotrimethylsilane or fV-methyl-IV-trimethylsilylacetamide were not able to promote the formation of monotrifluoromethylated amine, with the former leading to almost complete recovery of the starting trifluoromethyltrimethyl-silane while the latter induced decomposition of the imine. 

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