Silanes difluoromethyl

Fluoride ion-catalysed addition of trifluoromethyltrimethylsilane to acyl silanes occurs to give l,l-difluoro-2-trimethylsilyloxyalkenes (silyl enol ethers of difluoromethyl ketones), through nucleophilic addition of trifluoromethyl anion, Brook rearrangement and loss of fluoride. These compounds could be isolated when tetrabutylammonium difluorotriphenylstannate was used as a catalyst use of tetrabutylammonium fluoride gave the product corresponding to subsequent aldol reaction with the difluoromethyl ketone (Scheme 78)m. 

Analogously, the gas-phase thermal decomposition of trifluoro(l,l,2,2-tetrafluoroethyl)silane (at 140-200 C) or trimethyl(l,l,2,2-tetrafluoroethyI)silane (at 300-370°C) generated di-fluoromethyl(fluoro)carbene which underwent addition to alkenes to give 1-difluoromethyl-l-fluorocyclopropane 8. ° (Z)- and ( )-But-2-ene were cyclopropanated stereospecifically, and allylic C-H insertion was not observed. With dimethyl(vinyl)silane or allyl(dimeth-yl)silane, however, the carbene underwent both double bond addition and Si-H insertion. ... 

When a mixture of trifluoro(l,l,2,2-tetrafluoroethyl)silane and an alkane was thermolyzed, 1-difluoromethyl-l-fluorocyclopropanes were formed as byproducts in 7-11% yield. It is assumed that the generated carbene intermediate dehydrogenates the alkane, and that the resulting alkene is then cyclopropanated vide supra). 

Difluoromethyl-l-fluorocyclopropanes 3 were synthesized via pyrolysis of the corresponding silane in the presence of an alkene " (see Houben-Weyl, Vol. E19b, pp 1214-1215). 

The stereospecific addition to alkenes is consistent with (difluoromethyl)fluorocarbene being generated in the singlet state, Adducts of this carbene with alkenes were observed during the pyrolysis of trimethyl(l,l,2,2-tetrafluoroethyl)silane. ... 

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