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A new and highly versatile source of difluorocarbene is reported. Trimethyl
silyl fluorosulfonyldifluoroacetate (TFDA) undergoes decomposition in the p
resence of catalytic fluoride to form difluorocarbene under conditions that
allow its addition to relatively electron deficient alkenes in high yield.
For example, unprecedented CF2: addition to n-butyl acrylate proceeded in
73% yield.