Allylic Amination of Highly Substituted Alkenes Enabled by Photoredox Catalysis and Cu(II)-Mediated Radical-Polar Crossover

Copper-Catalyzed Allylic Amination of Alkenes Using O-Acylhydroxylamines: A Direct Entry to Diverse N-Alkyl Allylamines

We report a copper-catalyzed direct allylic amination of alkenes using readily available O-benzyolhydroxylamines as the alkylamine precursors and internal oxidant. A range of primary and secondary alkylamines can be installed onto diversely substituted alkenes for rapid construction of N-alkyl allylamines. Mechanistic studies support that the reaction engages an initial electrophilic amination to alkenes with anti-Markovnikov selectivity and subsequently a regioselective oxidative elimination to furnish the double bond transposition. In the electrophilic amination step, the use of strong Brønsted acid is critical for generating the key aminium radical cation (ARC) species.

Halide Perovskite Induces Halogen/Hydrogen Atom Transfer (XAT/HAT) for Allylic C-H Amination

Allylic C-H amination has emerged as a powerful tool to construct allylamines, common motifs in molecular therapeutics. Such reaction implies an oxidative path for C-H activation but furnishes reductive amines, inferring mild oxidants' inactivity for C-H oxidation but strong oxidants' detriment to products. Herein we report a heterogeneous catalytic approach that manipulates halogen-vacancies of perovskite photocatalyst and exploits halogenated-solvents (i.e. CH2Cl2, CH2Br2) as mild oxidants for selective C-H allyl amination with 19,376 turnovers. CsPbBr3 nanocrystals induce cooperative hydrogen-atom-transfer (HAT, C-H oxidation, and halogen-vacancy CsPbBr3-x formation) and halogen-atom-transfer (XAT, CsPbBr3-x-induced solvent reduction) under a radical chain mechanism. Terminal/internal olefins are amenable to forge aromatic/aliphatic, cyclic/acyclic, secondary/tertiary allylamines (70 examples), including drugs or their derivatives.

Recent advances in C(sp3)-N bond formation via metallaphoto-redox catalysis

The C(sp3)-N bond is ubiquitous in natural products, pharmaceuticals, biologically active molecules and functional materials. Consequently, the development of practical and efficient methods for C(sp3)-N bond formation has attracted more and more attention. Compared to the conventional ionic pathway-based thermal methods, photochemical processes that proceed through radical mechanisms by merging photoredox and transition-metal catalyses have emerged as powerful and alternative tools for C(sp3)-N bond formation. In this review, recent advances in the burgeoning field of C(sp3)-N bond formation via metallaphotoredox catalysis have been highlighted. The contents of this review are categorized according to the transition metals used (copper, nickel, cobalt, palladium, and iron) together with photocatalysis. Emphasis is placed on methodology achievements and mechanistic insight, aiming to inspire chemists to invent more efficient radical-involved C(sp3)-N bond-forming reactions.

Cu(II) salts as terminal oxidants in visible-light photochemical oxidation reactions

Photochemistry provides an important platform for the discovery of synthetically useful transformations. The development of new oxidative photoreactions, however, has proven to be relatively challenging. The importance of the identity of the terminal oxidant has been an underappreciated consideration in the design of these reactions. Many of the most common terminal oxidants used in ground-state catalytic methods are poorly compatible with the one-electron oxidation state changes characteristic of photoredox reactions and result in hard-to-control deleterious side reactions. As an alternative, Cu(II) salts have emerged as versatile terminal oxidants in photochemical oxidation reactions that are terrestrially abundant, cost-effective, and readily compatible with one-electron oxidation state changes. This review highlights recent reaction methods that leverage Cu(II) oxidation in combination with the photochemical activation of substrates or that use Cu(II) salts as both the active chromophore and terminal oxidant.