C 2-Symmetric 1,2-di(fluorenylidene)cyclobutanes: syntheses, structures, rearrangements and reactivity

Attempted deprotonation of 1,2-di(fluorenylidene)cyclobutane, 8, using n-butyl or tert-butyl-lithium led instead to 1,4-addition across the 1,3-butadiene unit to yield the 1-(9H-fluorenyl-2-(9-butyl-9H-fluorenyl)cyclobutene 10 or 11, respectively; analogously, n-butyl-lithium and trans-3,4-bis(trimethylsilyl)-1,2-di(fluorenylidene)cyclobutane, 12, furnished the corresponding 1,4-adduct 13. Bromination of 8 with N-bromosuccinimide led to mono-, …