Pd/Cu-cocatalyzed multi-site functionalization of in-situ generated alkenes toward carbazole-based aggregation-induced emission luminogens

Abstract

In contrast to the predominant mono or difunctionalization of alkenes, the multi-site functionalization of alkenes involving the synergistic formation of more than two new C–C or C–X bonds is much challenging, especially for developing new reaction pathway to afford the functional heterocycle compounds with aggregation-induced emission (AIE) property has been rarely reported. In present work, the multi-site functionalization of in situ generated alkenes with indoles has been developed for the synthesis of diversely functionalized carbazoles through the synergistic construction of multiple C–C bonds and C=O bond. A proposed reaction sequence involving C–H alkenylation/radical oxygen atom transfer/Diels-Alder cycloaddition/dehydrogenative aromatization was supported by experiments and density functional theory calculations. Further derivative carbazole-linked-quinoxaline skeletons represent a class of AIEgens with acceptor-donor-acceptor configuration, which generated the desired twisted intramolecular charge transfer (TICT) AIE properties and could be used as fluorescent probes for detecting the micrometer-sized phase separation of polymer blends. The protocol provides a concise route for the synthesis and application of carbazole-based AIE luminogens.