Calcium-Mediated C–H and C–F Bond Cleavage: Synthesis of Indenes and Perfluorodibenzopentalenes from 1,4-Dilithio-1,3-butadienes

The
development of Ca-mediated reactions is of great importance
and is in great demand in both organometallic and organic chemistry.
In this paper, we report that calcium iodide efficiently promotes
the transformation of various 1,4-dilithio-1,3-butadienes into indenes
or perfluorodibenzopentalenes, via an intramolecular C–H or
C–F bond cleavage, respectively. In the reaction process, the
Ca-induced s-cis/trans configurational isomerization
of 1,4-dilithio-1,3-butadienes is followed by the subsequent nucleophilic
C–H or C–F bond activation.