(Tetrafluorocyclobuty1) silanes prepared by thermal cycloaddition of tetrafluoroethylene (TFE) to vinylsilanes were pyrolyzed at 600 OC to give mixtures containing dimers of 1, 1, 2- trifluoro-1, 3-butadiene. The monomeric diene 1 was undoubtedly an intermediate formed by ring opening of initially formed 2, 3, 3-trifluoro-l-cyclobutene (9). This cyclobutene has been prepared by fluoride ion catalyzed removal of trimethylfluorosilane from (2, 2, 3, 3- ...