Photocatalytic Deuterium Atom Transfer Deuteration of Electron-Deficient Alkenes with High Functional Group Tolerance

Due to its mild reaction conditions and unique chemoselectivity, hydrogen atom transfer (HAT) hydrogenation represents an indispensable method for the synthesis of complex molecules. Its analog using deuterium, deuterium atom transfer (DAT) deuteration, is expected to enable access to complex deuterium-labeled compounds. However, DAT deuteration has been scarcely studied for synthetic purposes, and a method that possesses the favorable characteristics of HAT hydrogenations has remained elusive. Herein, we report a protocol for the photocatalytic DAT deuteration of electron-deficient alkenes. In contrast to the previous DAT deuteration, this method tolerates a variety of synthetically useful functional groups including haloarenes. The late-stage deuteration also allows access to deuterated amino acids as well as donepezil-d₂ . Thus, this work demonstrates the potential of DAT chemistry to become the alternative method of choice for preparing deuterium-containing molecules.

B(C6 F5 )3 -Catalyzed E-Selective Isomerization of Alkenes

Herein, we report the B(C₆ F₅ )₃ -catalyzed E-selective isomerization of alkenes. The transition-metal-free method is applicable across a diverse array of readily accessible substrates, giving access to a broad range of synthetically useful products containing versatile stereodefined internal alkenes. The reaction mechanism was investigated by using synthetic and computational methods.

Ligand-Controlled NiH-Catalyzed Regiodivergent Chain-Walking Hydroalkylation of Alkenes

A NiH-catalyzed migratory hydroalkylation of alkenyl amines with predictable and switchable regioselectivity is reported. By utilizing a ligand-controlled, directing group-assisted strategy, various alkyl units are site-selectively installed at inert sp³ C-H sites far away from the original C=C bonds. A range of structurally diverse α- and β-branched protected amines are conveniently synthesized via stabilization of 5- and 6-membered nickelacycles respectively. This method exhibits broad scope and high functional group tolerance, and can be applied to late-stage modification of medicinally relevant molecules.

Visible Light-Driven Molecular Switches and Motors: Recent Developments and Applications

Inspired by human vision, a diverse range of light-driven molecular switches and motors has been developed for fundamental understanding and application in material science and biology. Recently, the design and synthesis of visible light-driven molecular switches and motors have been actively pursued. This emerging trend is partly motivated to avoid the harmful effects of ultraviolet light, which was necessary to drive the classical molecular switches and motors at least in one direction, impeding their employment in biomedical and photopharmacology applications. Moreover, visible light-driven molecular switches and motors are demonstrated to enable benign optical materials for advanced photonic devices. Therefore, during the past several years, visible light-driven molecular switches based on azobenzene derivatives, diarylethenes, 1,2-dicyanodithienylethenes, hemithioindigo derivatives, iminothioindoxyls, donor-acceptor Stenhouse adducts, and overcrowded alkene based molecular motors have been judiciously designed, synthesized, and used in the development of functional materials and systems for a wide range of applications. In this Review, we present the recent developments toward the design of visible light-driven molecular switches and motors, with their applications in the fabrication of functional materials and systems in material science, bioscience, pharmacology, etc . The visible light-driven molecular switches and motors realized so far undoubtedly widen the scope of these interesting compounds for technological and biological applications. We hope this Review article could provide additional impetus and inspire further research interests for future exploration of visible light-driven advanced materials, systems, and devices.

Visible-Light-Induced Homolysis of Earth-Abundant Metal-Substrate Complexes: A Complementary Activation Strategy in Photoredox Catalysis

The mainstream applications of visible-light photoredox catalysis predominately involve outer-sphere single-electron transfer (SET) or energy transfer (EnT) processes of precious metal RuII or IrIII complexes or of organic dyes with low photostability. Earth-abundant metal-based Mn Ln -type (M=metal, Ln =polydentate ligands) complexes are rapidly evolving as alternative photocatalysts as they offer not only economic and ecological advantages but also access to the complementary inner-sphere mechanistic modes, thereby transcending their inherent limitations of ultrashort excited-state lifetimes for use as effective photocatalysts. The generic process, termed visible-light-induced homolysis (VLIH), entails the formation of suitable light-absorbing ligated metal-substrate complexes (Mn Ln -Z; Z=substrate) that can undergo homolytic cleavage to generate Mn-1 Ln and Z. for further transformations.

Expedient Dual Co/Organophotoredox Catalyzed Stereoselective Synthesis of All-Carbon Quaternary Centers

An efficient and attractive Co/organophotoredox dual catalysis protocol has been developed allowing the stereoselective access to a wide variety of syn-configured 1,3-diols featuring quaternary carbon centers. The synthesis of the target molecules is achieved under ambient reaction conditions using modular and accessible reagents, substituted vinyl cyclic carbonates and aldehydes, and in short reaction times. Mechanistic control experiments suggest that the stereoselectivity can be rationalized via a preferred Zimmerman-Traxler transition state comprising a Co(allyl) species and an activated aldehyde. This newly developed process thus expands the use of base metal catalysis in the construction of challenging quaternary carbon stereocenters.

Synthesis of Bioactive Diarylheptanoids from Alpinia officinarum and Their Mechanism of Action for Anticancer Properties in Breast Cancer Cells

An efficient synthesis of the Alpinia officinarum-derived diarylheptanoids, viz., enantiomers of a β-hydroxyketone (1) and an α,β-unsaturated ketone (2) was developed starting from commercially available eugenol. Among these, compound 2 showed a superior antiproliferative effect against human breast adenocarcinoma MCF-7 cells. Besides reducing clonogenic cell survival, compound 2 dose-dependently increased the sub G1 cell population and arrested the G2-phase of the cell cycle, as revealed by flow cytometry. Mechanistically, compound 2 acts as an intracellular pro-oxidant by generating copious amounts of reactive oxygen species. Compound 2 also induced both loss of mitochondrial membrane potential (MMP) as well as lysosomal membrane permeabilization (LMP) in the MCF-7 cells. The impaired mitochondrial and lysosomal functions due to reactive oxygen species (ROS)-generation by compound 2 may contribute to its apoptotic property.

Enantioselective Nickel-Catalyzed Migratory Hydrocyanation of Nonconjugated Dienes

Metal-catalyzed chain-walking reactions have recently emerged as a powerful strategy to functionalize remote positions in organic molecules. However, a chain-walking protocol for nonconjugated dienes remains scarcely reported, and developments are currently ongoing. In this Communication, a nickel-catalyzed asymmetric hydrocyanation of nonconjugated dienes involving a chain-walking process is demonstrated. The reaction exhibits excellent regio- and chemoselectivity, and a wide range of substrates were tolerated, delivering the products in high yields and enantioselectivities. Deuterium-labeling experiments support the chain-walking process, which involves an iterative β-H elimination and reinsertion processes. Gram-scale synthesis, regioconvergent experiments, and downstream transformations gave further insights into the high potential of this transformation.

Visible-Light Controlled Divergent Catalysis Using a Bench-Stable Cobalt(I) Hydride Complex

While the use of visible light in conjunction with transition metal catalysis offers powerful opportunities to switch between on/‐off states of catalytic activity, the next frontier would be the ability to switch the actual function of the catalyst and resulting products. Here we report such an example of multi‐dimensional catalysis. Featuring an easily prepared, bench‐stable cobalt(I) hydride complex in conjunction with pinacolborane, we can switch the reaction outcome between two widely employed transformations, olefin migration and hydroboration, with visible light as the trigger.

Regioselective Hydroalkylation and Arylalkylation of Alkynes by Photoredox/Nickel Dual Catalysis: Application and Mechanism

Alkynes are an important class of organic molecules due to their utility as versatile building blocks in synthesis. Although efforts have been devoted to the difunctionalization of alkynes, general and practical strategies for the direct hydroalkylation and alkylarylation of terminal alkynes under mild reaction conditions are less explored. Herein, we report a photoredox/nickel dual-catalyzed anti-Markovnikov-type hydroalkylation of terminal alkynes as well as a one-pot arylalkylation of alkynes with alkyl carboxylic acids and aryl bromides via a three-component cross-coupling. The results indicate that the transformations proceed via a new mechanism involving a single-electron transfer with subsequent energy-transfer activation pathways. Moreover, steady-state and time-resolved fluorescence-spectroscopy measurements, density functional theory (DFT) calculations, and wavefunction analysis have been performed to give an insight into the catalytic cycle.

Positional and Geometrical Isomerisation of Alkenes: The Pinnacle of Atom Economy

Strategies to achieve spatiotemporal regulation of pre-existing alkenes via external stimuli are essential given the ubiquity of feedstock olefins in chemistry and their downstream applications. Mirroring the 1-0 switch that underpins mammalian vision through selective geometric isomerisation in retinal, strategies to manipulate 2D space by both geometric and positional isomerisation of alkenes via chemical, thermal and light-driven processes are being intensively pursued. This minireview highlights the current state of the art in activating and achieving directionality in these fundamental chemical transformations.