Fluorinated Acyl Silanes

A variety of mono- and difluoroacetylsilanes and the corresponding silyl enol ethers were prepared from trifluoroethanol and chlorotrialkylsilanes in the presence of LDA through retro-Brook rearrangement. Sterically demanding silyl groups, especially those bound to oxygen, resulted in higher yields of difluoroacetylsilanes. The yields of difluoroacetylsilanes were also dramatically affected by the method of the termination of the reaction. Difluorohaloacetylsilanes were prepared from the corresponding difluoroethenyl silyl ethers with electrophilic halogenating reagents in good yields.

Scheme 1. Synthesis of difluoroacetyltrialkylsilanes

Scheme 2. Synthesis of monofluoroacetyltrialkylsilanes

The reactions of difluoroacetyltrialkylsilanes with methylidene triphenylphosphorane and benzylidene triphenylphosphorane are affected by the nature of the silyl substituents giving either the enol silyl ether or normal Wittig product exclusively, or mixture of both. Reactions with Horner-Emmons type ylide gave only the alkene products. Reactions of mono- and difluoroacetyltrialkylsilanes with dimethylsulfoxonium methylide gave the enol silyl ether products exclusively.

Scheme 3. Reactions of difluoroacetyltrialkylsilanes with phosphorus ylides.

• Publications:

  • Synthesis and utility of fluorinated acylsilanes, ACS Symposium Series (2005), 911(Fluorine-Containing Synthons), 378-398.
  • J. Org. Chem. 2004, 69, 6323-8.
  • Tetrahedron Lett. 2004, 45(28), 5403-6.
  • J. Fluorine Chem. 2002, 117(2), 207-211.