Polypyrrole as a Photothermal Reactor to Conduct Solvent-Free Pericyclic Reactions

Solvent-free organic reactions have proven to be a sustainable strategy in organic synthesis, such as mechanochemical, microwave-assisted, and ultrasound-irradiated methods. As a complementary strategy, photothermal materials may also be used in solvent-free chemistry. Polypyrroles, the black conjugated polymers, feature facile synthesis, high stability, and excellent light-harvesting capability, enabling them to serve as photothermal reactors to conduct solvent-free thermal-induced reactions. Here, a series of polypyrroles have been synthesized in the presence of various surfactants. The usage of dodecyl dimethyl betaine afforded PPy-BS, which achieved the highest photothermal performance (241°C under 100 W halogen-lamp irradiation). Scanning electron microscopy (SEM), Dynamic light scattering (DLS), and Brunauer-Emmett-Teller (BET) analyses suggest that the excellent photothermal performance of PPy-BS is likely attributed to the well-organized assembly based on the uniform particle. On this basis, PPy-BS was employed as a photothermal reactor for Diels-Alder, dipolar cycloaddition, and electrocyclization reactions under solvent-free conditions. All trials afforded good to excellent yields up to 90%. Notably, PPy-BS photothermal reactor exhibits excellent recyclability, a high loading amount of substrates, and upscaling to 1000 mg per batch. In brief, this study highlights the advantages of PPy-BS photothermal reactors for pericyclic reactions, offering a recyclable, up-scalable, and solvent-free platform for sustainable organic synthesis.