Direct difunctionalization of simple alkenes, the incorporation of two functional groups onto a carbon–carbon double bond, is of particular interest to the chemical community owing to its important applications in organic synthesis. Mechanistically, two types of reactions – metal‐catalyzed nucleophilic difunctionalization and radical difunctionalization – dominate this research field. Radical difunctionalization is more appealing from a synthetic perspective than metal‐catalyzed nucleophilic difunctionalization because it allows the conversion of simple alkenes into complex molecules in a rapid and convenient manner. Furthermore, radical difunctionalization allows addition to simple alkenes by various carbon‐centered radicals and even heteroatom‐centered radicals. This review gives an overview of intermolecular and intramolecular radical difunctionalization of simple alkenes, with an emphasis on the reaction patterns and mechanisms, as well as potential applications in synthetic chemistry.

Visible-light-responsive covalent organic frameworks (COFs) as photocatalysts for metal-free organic reactions are highly desirable due to their structural controllability and molecular functionality. In this study, we describe the fabrication of an anthraquinone functionalized COF linked by β-ketoenamines (AQ-COF), which presents a noodle-like nanofiber structure with staggered AB stacking mode. The as-resultant AQ-COF was efficiently utilized as a metal-free heterogeneous catalyst for selective aerobic oxidation of sulfides under visible-light irradiation. Compared with the precedential AQ-COFDMF with spherical particles, the proposed AQ-COF presents a higher photocatalytic activity with high selectivity to sulfoxides and chemical stability. Further characterization techniques revealed that the unique morphology and structure can greatly enhance charge transfer and separation efficiency of photogenerated electron–hole pairs, thus giving rise to the improvement of photocatalytic activity.

Covalent triazine frameworks (CTFs) with donor–acceptor motifs have been identified as prospective semiconducting materials for photocatalysis. Though donor–acceptor motifs can favor forward intramolecular charge separation, some cases still suffer from backward charge recombination, resulting in the decrease of the photocatalytic activity. Herein, acetylene-bridged CTFs bearing an extended donor−π–acceptor motif was fabricated to prompt exciton dissociation. Experimental investigations and density functional theory calculations prove that the acetylene moiety can suppress backward charge recombination, minimize exciton binding energy, and enhance charge carrier lifetime, thereby prompting forward charge transfer/separation in comparison to the analogous one without acetylene. Thus, the acetylene-bridged CTFs showcased a higher photocatalytic activity for metal-free photocatalytic oxidative amines coupling with oxygen under visible-light irradiation, and apparent quantum efficiency at 420 nm was achieved up to 32.3%, that is, twofold higher than the one without acetylene. Furthermore, the acetylene moieties can adsorb oxygen molecules and provide active sites to lower the energy barrier and thus significantly enable the photoredox catalysis. This work provides alternative insights into the design and construction of high-performance CTFs, with prospective applications in solar-to-chemical energy conversion.