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Site selectivity represents a key challenge for non-directed C−H functionalization, even when the C−H bond is intrinsically reactive. Here, we report a copper-catalyzed method for benzylic C−H azidation of diverse molecules. Experimental and density functional theory studies suggest the benzyl radical reacts with a Cu II -azide species via a radical-polar crossover pathway. Comparison of this method with other C−H azidation methods highlights its unique site selectivity, and conversions of the benzyl azide products into amine, triazole, tetrazole, and pyrrole functional groups highlight the broad utility of this method for target molecule synthesis and medicinal chemistry.

Azoles are important motifs in medicinal chemistry, and elaboration of their structures via direct N−H/C−H coupling could have broad utility in drug discovery. The ambident reactivity of many azoles, however, presents significant selectivity challenges. Here, we report a copper-catalyzed method that achieves site-selective cross-coupling of pyrazoles and other N−H heterocycles with substrates bearing (hetero)benzylic C−H bonds. Excellent N-site selectivity is achieved, with the preferred site controlled by the identity of co-catalytic additives. This cross-coupling strategy features broad scope for both the N−H heterocycle and benzylic C−H coupling partners, enabling application of this method to complex molecule synthesis and medicinal chemistry.

Copper-catalyzed radical-relay reactions provide a versatile strategy for selective C–H functionalization; however, reactions with peroxide-based oxidants often require excess C–H substrate. Here, we report a photochemical strategy to overcome this limitation by using a Cu/2,2′-biquinoline catalyst that supports benzylic C–H esterification with limiting C–H substrate. Mechanistic studies indicate that blue-light irradiation promotes carboxylate-to-copper charge transfer, reducing resting-state CuII to CuI, which activates the peroxide to generate an alkoxyl radical hydrogen-atom-transfer species. This “photochemical redox buffering” introduces a unique strategy to sustain the activity of Cu catalysts in radical-relay reactions.

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Heterocycles are the backbone of modern medical chemistry and drug development. The derivatization of “an olefin” inside aromatic rings represents an ideal approach to access functionalized saturated heterocycles from abundant aromatic building blocks. Here, we report an operationally simple, efficient, and practical method to selectively access hydrosilylated and reduced N-heterocycles from bicyclic aromatics via a key diradical intermediate. This approach is expected to facilitate complex heterocycle functionalizations that enable access to novel medicinally relevant scaffolds.

Aluminum metal matrix composites (Al-MMCs) are new promising materials for aviation, aerospace and automotive industries. However, due to the poor weldability they have very limited applications. In this paper, the authors present the welding achievements of Al-MMCs developed by their scientific research team in recent years. Laser welding, liquid phase impact diffusion welding and vacuum brazing were utilized. Based on analysis of microstructure, good joints can be achieved by using these welding methods.

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