Xiao Zhang

Reversible formation and cleavage of covalent bonds hold promise for organic synthesis, polymeric materials, dynamic covalent networks, and drug delivery. However, such reversibility has predominantly relied on labile covalent bonds, such as ester, thioester, amide, and disulfide bonds. Herein, we report the reversible formation and cleavage of conventionally irreversible C─C and C─Br bonds enabled by an organic photocatalyst. Using the single photocatalyst isosulfonyltruxene ( ITSO ₂ ), we accomplish reductive pinacol coupling of ketones to vicinal diols and the reverse oxidative cleavage. Moreover, this system also facilitates oxidative bromination of alkenes to vicinal dibromides and the reverse reductive debromination. Notably, this platform proves applicable to the synthesis and degradation of polymeric diols, as well as reversible modification of rubber. Mechanistic studies reveal that ITSO ₂ inherently exhibits potent oxidizing capacity to facilitate oxidative C─C bond cleavage and C─Br bond formation, which can be converted into highly reducing photoactive species under net‐reductive photochemical conditions, thereby enabling reductive C─C bond formation and C─Br bond cleavage.

Visible‐light photoredox catalysis offers a promising approach to convert indoles into functionalized indoles and indolines under mild conditions. However, existing methods often rely on iridium or ruthenium polypyridyl photocatalysts, which suffered from sustainability concerns and limited scope. Here, we report a transition‐metal‐free protocol for diverse indole transformations using catechol‐derived organic photocatalysts that feature balanced redox potentials and broad reactivity. Three mechanistically distinct transformations of indoles including aerobic bromination, dearomative carbamoylation, and dearomative reduction or detosylation have been achieved under net oxidative, redox‐neutral, and net reductive conditions, respectively. A variety of bromoindoles, carbamoyl‐indolines, and functionalized indolines or free N–H indoles are obtained in good yields under mild, transition‐metal‐free conditions. This article provides a sustainable and versatile entry to indole transformations.

Dearomatization reactions constitute a powerful strategy to convert aromatic compounds into three-dimensional scaffolds, which have found wide applications in organic synthesis, medicinal chemistry, and materials science. Distinct from ground-state dearomatization, the photosensitized dearomatization of (hetero)arenes capitalizes on excited-state reactivities, enabling the achievement of thermodynamically disfavoured transformations along with the generation of intriguing scaffolds. This review summarizes recent advances in the photosensitized dearomatization of (hetero)arenes according to the type of (hetero)arene. Mediated by appropriate photosensitizers, a series of (hetero)arenes are engaged in photocycloaddition, difunctionalization, or sensitized reduction.

A pair of photocatalysts with opposing strongly reducing and oxidizing capacities has been developed by modulating the heteroatom valence states.

Isoazatruxene and its derivatives, which can be readily synthesized via cyclotrimerization, have been discovered as novel organic photocatalysts with high catalytic performance. However, the N-unsubstituted isoazatruxene (ITN-1) shows poor absorption in the visible region. Herein, we report that treatment of ITN-1 with Cs₂CO₃ generates the N-centered isoazatruxene anionic species (ITN³⁻), which exhibits enhanced visible-light absorption and potent reducing ability. Under the photocatalysis of ITN³⁻, the dehalogenative arylation and phosphorylation of aryl halides can be efficiently achieved, enabling the rapid assembly of pyrrole-containing biaryls and aryl phosphonates. The synthetic utility is further demonstrated by late-stage modification of complex molecules and multi-phosphorylation. Mechanistic studies confirm that the deprotonation of isoazatruxene results in enhanced visible-light absorption and improved photophysical properties.

A dual catalysis involving both anionic and cationic species of an ion-pairing photocatalyst is achieved. By adopting this mode of action, photocatalytic hydrogen transfer and cross-coupling reactions can be enabled using a single photocatalyst.