Synthesis of cyclophanes via an intermolecular Pd-catalyzed enyne-diyne cross-benzannulation approach

Several novel types of cyclophanes were efficiently synthesized via an inte rmolecular palladium-catalyzed cross-benzannulation of cyclic enynes and di ynes. These types of cyclophanes are not accessible through an intramolecul ar mode of the homo-benzannulation protocol, reported previously. Cyclic re actants (enynes and diynes) were readily prepared in reasonable yields from commercially available materials using known procedures. The fact that the cyclic Z-enyne 29, in contrast to its E-counterpart, underwent benzannulat ion to produce the cyclophane 28 brought additional support for the necessi ty of having an E-hydrogen atom at the terminal olefin moiety of nonactivat ed enynes, which was found previously in the benzannulation of the acyclic susbstrates.