Twofold Alkenylation of Thiophenes with N-Vinylcarbazole via Iron-Catalyzed Regioselective C−H/C−H Coupling

Abstract

The incorporation of the vinylene motif into conjugated molecules notably elevates the HOMO level, augmenting both emissive and conductive properties while enhancing responsiveness to external stimuli. This study focuses on the regioselective C−H/C−H coupling of N-vinylcarbazole with thiophenes, offering an efficient route to N-vinylene-incorporated conjugated molecules for the development of organic electronic materials. Traditional palladium-catalyzed Fujiwara-Moritani (FM) reactions proved ineffective for C−H alkenylation with N-vinylcarbazole. In response, we have developed an iron-catalyzed twofold alkenylation method for conjugated thiophenes with N-vinylcarbazole, utilizing trimethylaluminum as the base and diethyl oxalate as the oxidant. This reaction occurs regioselectively at the C₂−H (or C₅−H) bond of the thiophenes and the terminal position of N-vinylcarbazole. It also successfully produces short thiophene polymers end-capped with N-vinylcarbazole, demonstrating the potential for synthesizing polymeric donor materials. The enamine products exhibit blue-to-green emission, high fluorescence quantum yield, and visible light responsivity for stereo-isomerization, indicating promising applications in organic electronics.