3-Methyl-3-(2,3,5,6-tetrafluoro-4-nitrophenyl)-1,5-dioxaspiro[5.5]undecane-2,4-dione

This compound undergoes cycloreversion to form the fluoro(hetero)aryl ketene, which undergoes efficient coupling with nucleophiles and allows rapid incorporation of highly fluorinated α-fluoro(hetero)aryl acetic acid derivatives.