Structurally Diverse π-Extended Conjugated Polycarbo- and Heterocycles through Pd-Catalyzed Autotandem Cascades

The Pd-catalyzed reaction between 2,2'-dibromobiphenyls and related systems with tosylhydrazones gives rise to new π-extended conjugated polycarbo- and heterocycles through an autotandem process involving a cross-coupling reaction followed by an intramolecular Heck cyclization. The reaction shows wide scope regarding both coupling partners. Cyclic and acyclic tosylhydrazones can participate in the process. Additionally, a variety of aromatic and heteroaromatic dibromoderivatives have been employed, leading to an array of diverse scaffolds featuring a fluorene or acridine central nucleus, and containing binaphthyl, thiophene, benzothiophene and indole moieties. The application to appropriate tetrabrominated systems led to greater structural complexity through two consecutive autotandem cascades. The photophysical properties of selected compounds were studied through their absorption and emission spectra. Fluorescence molecules featuring very high quantum yields were identified, showing the potential of this methodology in the development of molecules with interesting optoelectronic properties.