Iron-Catalyzed Aza-Annulative π-Extension with Alkynes via C–H Activation using an Oxidative Auxiliary

Abstract: Aza-annulative π-extension (AAPE) reactions offer a potent pathway to create novel donor-acceptor conjugated materials by integrating an imine moiety into the conjugated system, serving as an electron-accepting unit. However, the affinity of late-transition metals for conjugated π-systems, coupled with their elevated cost, has posed significant challenges, restricting efficient AAPE reactions on straightforward C–H substrates for developing conjugated new materials. In this study, we unveil an iron-catalyzed C–H activation methodology, facilitating AAPE with diverse internal alkynes and employing oxime ether as both a self-oxidizing auxiliary and nitrogen source, derived seamlessly from accessible carbonyl compounds. The AAPE reaction was enabled by using trisphosphine as a ligand, and isobutyl aluminum(III) catecholate as a base. By using the reaction, we discovered an aza-oxa[5]helicene from dixanthone as a potential circularly polarized luminescence material and two narrow-band-emissive molecules from easily accessible pentacene-6,13-dione and quinacridone, which emit blue and yellow light with high color purity and high fluorescence quantum yield. These findings emphasize the potential of iron-catalyzed C–H activation in expanding the range of donor-acceptor-type conjugated materials for organic electronics.