The merging of click chemistry with discrete photochemical processes has led to the creation of a new class of click reactions, collectively known as photoclick chemistry. These light-triggered click reactions allow the synthesis of diverse organic structures in a rapid and precise manner under mild conditions. Because light offers unparalleled spatiotemporal control over the generation of the reactive intermediates, photoclick chemistry has become an indispensable tool for a wide range of spatially addressable applications including surface functionalization, polymer conjugation and cross-linking, and biomolecular labeling in the native cellular environment. Over the past decade, a growing number of photoclick reactions have been developed, especially those based on the 1,3-dipolar cycloadditions and Diels–Alder reactions owing to their excellent reaction kinetics, selectivity, and biocompatibility. This review summarizes the recent advances in the development of photoclick reactions and their applications in chemical biology and materials science. A particular emphasis is placed on the historical contexts and mechanistic insights into each of the selected reactions. The in-depth discussion presented here should stimulate further development of the field, including the design of new photoactivation modalities, the continuous expansion of λ-orthogonal tandem photoclick chemistry, and the innovative use of these unique tools in bioconjugation and nanomaterial synthesis.

Site selectivity is an inherent challenge in C–H functionalization reactions. The most intensively sought‐after approaches have involved the employment of Lewis‐basic coordinating groups to direct a metal to a proximal site, in the process generating a metallacycle capable of further organometallic reactivity. In the recent years considerable effort has been directed towards the development of new transformations involving transition‐metal‐mediated C–H functionalization directed by weakly coordinating groups. This microreview focuses on the role and utility of amides and anilides in directed, proximal C–H bond functionalization reactions.

A new ruthenium-catalyzed, heteroatom-directed strategy for C–H allylation of indoles is described. The use of allyl alcohols as coupling partners as well as pyridine as the removable directing group is highlighted. This methodology provides access to C2-allylated indoles by utilizing a strategy that does not require prefunctionalization of either of the coupling partners.

Here we report the design of a superfast bioorthogonal ligation reactant pair comprising a sterically shielded, sulfonated tetrazole and bicyclo[6.1.0]­non-4-yn-9-ylmethanol (BCN). The design involves placing a pair of water-soluble N-sulfonylpyrrole substituents at the C-phenyl ring of diphenyltetrazoles to favor the photoinduced cycloaddition reaction over the competing nucleophilic additions. First-principles computations provide vital insights into the origin of the tetrazole–BCN cycloaddition’s superior kinetics compared to the tetrazole–spirohexene cycloaddition. The tetrazole–BCN cycloaddition also enabled rapid bioorthogonal labeling of glucagon receptors on live cells in as little as 15 s.

A unique, ruthenium-catalyzed, [3 + 3] annulation of anilines with allyl alcohols in the synthesis of substituted quinolines is reported. The method employs a traceless directing group strategy in the proximal C-H bond activation and represents a one-pot Domino synthesis of quinolines from anilines.