Dual Nickel‐ and Photoredox‐Catalyzed Enantioselective Desymmetrization of Cyclic meso‐Anhydrides

The enantioselective desymmetrization of cyclic meso‐anhydrides with benzyl trifluoroborates under nickel‐photoredox catalysis is described. The reaction tolerates a variety of sterically and electronically different trifluoroborates, as well as structurally unique cyclic anhydrides. The trans isomer of the keto‐acid products is also observed at varying levels dependent on the trifluoroborate identity and relative catalyst loading. A mechanism involving decarbonylation and Ni−C bond homolysis of a Ni^II adduct is proposed. This feature allows access to a trans keto‐acid as the major product in high enantioselectivity from a cis meso anhydride.     

Organocatalytic Enantioselective Protonation for Photoreduction of Activated Ketones and Ketimines Induced by Visible Light

The first catalytic asymmetric photoreduction of 1,2‐diketones and α‐keto ketimines under visible light irradiation is reported. A transition‐metal‐free synergistic catalysis platform harnessing dicyanopyrazine‐derived chromophore (DPZ) as the photoredox catalyst and a non‐covalent chiral organocatalyst is effective for these transformations. With the flexible use of a chiral Brønsted acid or base in H⁺ transfer interchange to control the elusive enantioselective protonation, a variety of chiral α‐hydroxy ketones and α‐amino ketones were obtained with high yields and enantioselectivities.     

Hydrotrifluoromethylthiolation of Unactivated Alkenes and Alkynes with Trifluoromethanesulfonic Anhydride through Deoxygenative Reduction and Photoredox Radical Processes

An ongoing challenge in trifluoromethylthiolation reactions is the use of less expensive and easily available trifluoromethylthio sources. Herein, we disclose an unprecedented usage of trifluoromethanesulfonic anhydride (Tf₂O) as a radical trifluoromethylthiolating reagent. Hydrotrifluoromethylthiolation of unactivated alkenes and alkynes with Tf₂O in the presence of PMePh₂ and H₂O under visible‐light photoredox catalysis gave the addition products. The trifluoromethylthio radical (^.SCF₃) was first formed from Tf₂O through a photoredox radical processes and deoxygenative reduction of PMePh₂, and H₂O serves as the H‐atom donor for the hydrotrifluoromethylthiolation reaction. This reaction provides a new strategy for radical trifluoromethylthiolation.     

Asymmetric Total Syntheses of the Akuammiline Alkaloids (−)‐Strictamine and (−)‐Rhazinoline

Strictamine and rhazinoline are representative methanoquinolizidine‐containing akuammiline alkaloids that possess different stereochemistry at the C16 position. A unified approach to the enantioselective total syntheses of these two molecules is described. The key steps in this synthesis include a photocatalytic intra/intermolecular type II radical cascade reaction, a Tsuji–Trost allylation, a palladium‐ or nickel‐mediated cyclization, and a late‐stage intramolecular N‐alkylation reaction.     

The Dual Role of Benzophenone in Visible‐Light/Nickel Photoredox‐Catalyzed C−H Arylations: Hydrogen‐Atom Transfer and Energy Transfer

A dual catalytic protocol for the direct arylation of non‐activated C(sp³)?H bonds has been developed. Upon photochemical excitation, the excited triplet state of a diaryl ketone photosensitizer abstracts a hydrogen atom from an aliphatic C?H bond. This inherent reactivity was exploited for the generation of benzylic radicals which subsequently enter a nickel catalytic cycle, accomplishing the benzylic arylation.