The reaction of perfluoro-1,2-dichlorocyclobutene with t-butyllithium leads to replacement of Cl by Li. The lithio derivative was stable to -30°C and reaction with trimethylsilyl chloride gave perfluoro-1-chloro-2-trimethylsilylcyclobutene. The reaction of the latter with t-butyllithium leads to dehalogenation and the addition of t-butyl to form a dimeric compound. The reaction of 1-chloro-2,2,3,3-tetrafluorocyclobutene with phenyllithium followed by treatment with deuterium oxide gave perfluoro-1-phenylcyclobutene-2-d 1 , suggesting that perfluorocyclobutyne may have been an intermediate.