Solid-phase approaches toward cyclic oligomers

Strategies were sought to effect cyclizations of oligo(m-phenylene ethynylene) by exploiting pseudo-high dilution effects on polymer supports. Using Pd/Cu-catalyzed coupling protocols, Merrifieldʹs resin (1% crosslinked chloromethylated polystyrene) proved inadequate for site isolation; inter-site couplings ensued on the flexible support. Conversely, use of the Argopore resin, a more highly crosslinked polystyrene, inhibited inter-site interactions, and no identifiable final product could be separated from the resin. Spectroscopic and mass spectrometric methods indicated that the product from the Argopore resin might be a threaded catenane.