γ-Functionalizations of Amines through Visible-Light-Mediated, Redox-Neutral C−C Bond Cleavage

Visible-Light Induced C(sp2 )-H Amidation with an Aryl-Alkyl σ-Bond Relocation via Redox-Neutral Radical-Polar Crossover

We report an approach for the intramolecular C(sp² )-H amidation of N-acyloxyamides under photoredox conditions to produce δ-benzolactams with an aryl-alkyl σ-bond relocation. Computational studies on the designed reductive single electron transfer strategy led us to identify N-[3,5-bis(trifluoromethyl)benzoyl] group as the most effective amidyl radical precursor. Upon the formation of an azaspirocyclic radical intermediate by the selective ipso-addition with outcompeting an ortho-attack, radical-polar crossover was then rationalized to lead to the rearomative ring-expansion with preferential C-C bond migration.

Radical 1,4-Aryl Migration Enabled Remote Cross-Electrophile Coupling of α-Amino-β-Bromo Acid Esters with Aryl Bromides

We report an unprecedented, efficient nickel-catalysed radical relay for the remote cross-electrophile coupling of β-bromo-α-benzylamino acid esters with aryl bromides via 1,4-aryl migration/arylation cascades. β-Bromo-α-benzylamino acid esters are considered as unique molecular scaffolds allowing for aryl migration reactions, which are conceptually novel variants for the radical Truce-Smiles rearrangement. This reaction enables the formation of two new C(sp³ )-C(sp² ) bonds using a bench-stable Ni/bipyridine/Zn system featuring a broad substrate scope and excellent diastereoselectivity, which provides an effective platform for the remote aryl group migration and arylation of amino acid esters via redox-neutral C(sp³ )-C(sp² ) bond cleavage. Mechanistically, this cascade reaction is accomplished by combining two powerful catalytic cycles consisting of a cross-electrophile coupling and radical 1,4-aryl migration through the generation of C(sp³ )-centred radical intermediates from the homolysis of C(sp³ )-Br bonds and the switching of the transient alkyl radical into a robust α-aminoalkyl radical.

Visible-Light Photoredox-Catalyzed Remote Difunctionalizing Carboxylation of Unactivated Alkenes with CO2

Remote difunctionalization of unactivated alkenes is challenging but a highly attractive tactic to install two functional groups across long distances. Reported herein is the first remote difunctionalization of alkenes with CO₂ . This visible-light photoredox catalysis strategy provides a facile method to synthesize a series of carboxylic acids bearing valuable fluorine- or phosphorus-containing functional groups. Moreover, this versatile protocol shows mild reaction conditions, broad substrate scope, and good functional-group tolerance. Based on DFT calculations, a radical adds to an unactivated alkene to smoothly form a new carbon radical, followed by a 1,5-hydrogen atom-transfer process, the rate-limiting step, generating a more stable benzylic radical. The reduction of the benzylic radicals by an Ir^II species generates the corresponding benzylic carbanions as the key intermediates, which further undergo nucleophilic attack with CO₂ to generate carboxylates.

DMSO-Enabled Selective Radical O-H Activation of 1,3(4)-Diols

Control of selectivity is one of the central topics in organic chemistry. Although unprecedented alkoxyl-radical-induced transformations have drawn a lot of attention, compared to selective C-H activation, selective radical O-H activation remains less explored. Herein, we report a novel selective radical O-H activation strategy of diols by combining spatial effects with proton-coupled electron transfer (PCET). It was found that DMSO is an essential reagent that enables the regioselective transformation of diols. Mechanistic studies indicated the existence of the alkoxyl radical and the selective interaction between DMSO and hydroxyl groups. Moreover, the distal C-C cleavage was realized by this selective alkoxyl-radical-initiation protocol.

Few-layer Black Phosphorous Catalyzes Radical Additions to Alkenes Faster than Low-valence Metals

The substitution of catalytic metals by p-block main elements has a tremendous impact not only in the fundamentals but also in the economic and ecological fingerprint of organic reactions. Here we show that few-layer black phosphorous (FL-BP), a recently discovered and now readily available 2D material, catalyzes different radical additions to alkenes with an initial turnover frequency (TOF0) up to two orders of magnitude higher than representative state-of-the-art metal complex catalysts at room temperature. The corresponding electron-rich BP intercalation compound (BPIC) KP6 shows a nearly twice TOF0 increase with respect to FL-BP. This increase in catalytic activity respect to the neutral counterpart also occurs in other 2D materials (graphene vs. KC8) and metal complex catalysts (Fe0 vs. Fe2- carbon monoxide complexes). This reactive parallelism opens the door for cross-fertilization between 2D materials and metal catalysts in organic synthesis.

Photocatalyzed allylic derivatization reactions

Catalytic allylation reactions are important methodologies to produce fine chemicals and synthetic building blocks. This review discloses state-of-the-art photocatalyzed allylation methodologies, their reaction mechanisms, and synthetic applications.

Aliphatic Radical Relay Heck Reaction at Unactivated C(sp3 )-H Sites of Alcohols

The Mizoroki-Heck reaction is one of the most efficient methods for alkenylation of aryl, vinyl, and alkyl halides. Given its innate nature, this protocol requires the employment of compounds possessing a halogen atom at the site of functionalization. However, the accessibility of organic molecules possessing a halogen atom at a particular site in aliphatic systems is extremely limited. Thus, a protocol that allows a Heck reaction to occur at a specific nonfunctionalized C(sp3 )-H site is desirable. Reported here is a radical relay Heck reaction which allows selective remote alkenylation of aliphatic alcohols at unactivated β-, γ-, and δ-C(sp3 )-H sites. The use of an easily installed/removed Si-based auxiliary enables selective I-atom/radical translocation events at remote C-H sites followed by the Heck reaction. Notably, the reaction proceeds smoothly under mild visible-light-mediated conditions at room temperature, producing highly modifiable and valuable alkenol products from readily available alcohols feedstocks.

Direct Photocatalytic Synthesis of Medium-Sized Lactams by C-C Bond Cleavage

Reported is a novel two-step ring-expansion strategy for expeditious synthesis of all ring sizes of synthetically challenging (hetero)aryl-fused medium-sized lactams from readily available 5-8-membered cyclic ketones. This step-economic approach features a remote radical (hetero)aryl migration from C to N under visible-light conditions. Broad substrate scope, good functional-group tolerance, high efficiency, and mild reaction conditions make this procedure very attractive. In addition, this method also provides expedient access to 13-15-membered macrolactams upon an additional one-step manipulation. Mechanistic studies indicate that the reaction involves an amidyl radical and is promoted by acid.

Photoinduced Remote Functionalization of Amides and Amines Using Electrophilic Nitrogen Radicals

The selective functionalization of C(sp3 )-H bonds at distal positions to functional groups is a challenging task in synthetic chemistry. Reported here is a photoinduced radical cascade strategy for the divergent functionalization of amides and protected amines. The process is based on the oxidative generation of electrophilic amidyl radicals and their subsequent transposition by 1,5-H-atom transfer, resulting in remote fluorination, chlorination and, for the first time, thioetherification, cyanation, and alkynylation. The process is tolerant of most common functional groups and delivers useful building blocks that can be further elaborated. The utility of this strategy is demonstrated through the late-stage functionalization of amino acids and a dipeptide.

Photoinduced Remote Functionalisations by Iminyl Radical Promoted C-C and C-H Bond Cleavage Cascades

A photoinduced cascade strategy leading to a variety of differentially functionalised nitriles and ketones has been developed. These reactions rely on the oxidative generation of iminyl radicals from simple oximes. Radical transposition by C(sp3 )-(sp3 ) and C(sp3 )-H bond cleavage gives access to distal carbon radicals that undergo SH 2 functionalisations. These mild, visible-light-mediated procedures can be used for remote fluorination, chlorination, and azidation, and were applied to the modification of bioactive and structurally complex molecules.

Photoredox Imino Functionalizations of Olefins

Shown herein is that polyfunctionalized nitrogen heterocycles can be easily prepared by a visible-light-mediated radical cascade process. This divergent strategy features the oxidative generation of iminyl radicals and subsequent cyclization/radical trapping, which allows the effective construction of highly functionalized heterocycles. The reactions proceed efficiently at room temperature, utilize an organic photocatalyst, use simple and readily available materials, and generate, in a single step, valuable building blocks that would be difficult to prepare by other methods.