Selective Radical-Radical Cross-Couplings: Design of a Formal β-Mannich Reaction

Reductive annulations of arylidene malonates with unsaturated electrophiles using photoredox/Lewis acid cooperative catalysis

A cooperative Lewis acid/photocatalytic reduction of salicylaldehyde-derived arylidene malonates provides access to a versatile, stabilized radical anion enolate. Using these unusual umpolung operators, we have developed a novel route to access densely functionalized carbo- and heterocycles through a radical annulation addition pathway.

Electrochemical oxidative C-H/S-H cross-coupling between enamines and thiophenols with H2 evolution

Electrochemical oxidative C-H/S-H cross-coupling has been developed to construct the C-S bond in a highly straightforward and efficient manner. Various enamines and (hetero)aryl thiols could be transformed smoothly under undivided electrolytic cell conditions. Moreover, this electrosynthesis strategy not only avoided the use of chemical oxidants and transition metal catalysts, but also exhibited excellent atom economy.

Recent advances in photocatalytic manipulations of Rose Bengal in organic synthesis

This review highlights the recent advances in photocatalytic manipulations of Rose Bengal in organic synthesis.

Photocatalyzed transfer hydrogenation and deuteriation of cyclic N-sulfonylimines

Photocatalyzed transfer hydrogenation of cyclic N-sulfonylimines by using water as the hydrogen source is described.

Photo- and dioxygen-enabled radical C(sp3)–N(sp2) cross-coupling between guanidines and perfluoroalkyl iodides

The utilization of visible light and dioxygen (air) as green and sustainable mediators in photocatalyzed synthetic chemistry is demonstrated.

Catalytic alkylation of unactivated C(sp3)–H bonds for C(sp3)–C(sp3) bond formation

This review summarizes recent advancements in catalytic direct transformation of unactivated C(sp³)–H bonds into C(sp³)–C(sp³) bonds.

Photocatalytic Barbier reaction - visible-light induced allylation and benzylation of aldehydes and ketones

We report a photocatalytic version of the Barbier type reaction using readily available allyl or benzyl bromides and aromatic aldehydes or ketones as starting materials to generate allylic or benzylic alcohols. The reaction proceeds at room temperature under visible light irradiation with the organic dye 3,7-di(4-biphenyl)1-naphthalene-10-phenoxazine as a photocatalyst and DIPEA as sacrificial electron donor. The proposed cross-coupling mechanism of a ketyl- and an allyl or benzyl radical is supported by spectroscopic investigations and cyclic voltammetry measurements.

Photocatalytic reverse polarity Povarov reaction

A visible light mediated iridium photocatalysed reverse polarity Povarov reaction of aryl imines and electron deficient alkenes is described. Operating via a putative nucleophilic α-amino radical, generated by a proton coupled electron transfer process, addition to a range of conjugated electron deficient alkene substrates affords substituted tetrahydroquinoline products in high yields and with typically good to excellent diastereoselectivity in favor of the trans diastereoisomer. Sub-stoichiometric quantities of Hantzsch ester were found to be key to initiate the overall redox-neutral, free radical cyclization cascade. This new reaction complements existing two electron Lewis acid mediated variants and expands the capabilities of imine umpolung chemistry to synthetically relevant cyclisation methodology.

Direct β-Alkylation of Ketones and Aldehydes via Pd-Catalyzed Redox Cascade

We report a direct β-alkylation of ketones and aldehydes with simple alkyl bromides through a Pd-catalyzed redox-cascade strategy. The use of a Cu cocatalyst is important for improved efficiency. The reaction is redox-neutral, without the need for strong acids or bases. Both cyclic and acyclic ketones, as well as α-branched aldehydes, are suitable substrates for coupling with secondary and tertiary alkyl bromides. Concise formal synthesis of Zanapezil is achieved using this β-alkylation method.

A Synthetic Route to Sodium α-Aminoalkanesulfinates and Their Application in the Generation of α-Aminoalkyl Radicals for Radical Addition Reactions

The synthesis of sodium α-aminoalkanesulfinates and their synthetic utility as α-aminoalkyl radical precursors are reported. A variety of α-aminoalkanesulfinates were readily obtained from the reaction between the anions of N-Boc-protected alkylamines and 1,4-diazabicyclo[2.2.2]octanebis(sulfur dioxide). Treatment of sodium α-aminoalkanesulfinates with (diacetoxyiodo)benzene easily generated the corresponding α-aminoalkyl radicals under mild conditions, which were then applied in radical 1,2-addition to imines, radical 1,4-addition to electron-deficient olefins, and radical addition/cyclization to 2-isocyanobiphenyls.

Synergistic Photoredox Catalysis and Organocatalysis for Inverse Hydroboration of Imines

The first catalytic inverse hydroboration of imines with N-heterocyclic carbene (NHC) boranes has been realized by means of cooperative organocatalysis and photocatalysis. This catalytic combination provides a promising platform for promoting NHC-boryl radical chemistry under sustainable and radical-initiator-free conditions. The highly important functional-group compatibility and possible application in late-stage hydroborations represent an important step forward to an enhanced α-amino organoboron library.

Catalytic Asymmetric β-C-H Functionalizations of Ketones via Enamine Oxidation

A chiral primary amine catalyzed oxidative β-C-H functionalization of ketone is described. The reaction proceeds via ketone enamine oxidation by IBX and enables highly enantioselective remote C-H functionalization of both cyclic and acyclic ketones, generating chiral ketones bearing β-stereocenters.

Multifunctionalization of Unactivated Cyclic Ketones via Synergistic Catalysis of Copper and Diarylamine: Access to Cyclic α-Enaminone

A multifunctionalization of unactivated cyclic ketones via synergistic catalysis of copper and diarylamine for the direct synthesis of cyclic α-enaminone is reported for the first time. This reaction goes through oxidative α-amination, followed by a desaturation, and features mild reaction conditions, a broad substrate scope, and great functional group tolerance.

Reductive Amination by Photoredox Catalysis and Polarity-Matched Hydrogen Atom Transfer

The excitation of a Ru^II photosensitizer in the presence of ascorbic acid leads to the reduction of iminium ions to electron-rich α-aminoalkyl radical intermediates, which are rapidly converted into reductive amination products by thiol-mediated hydrogen atom transfer (HAT). As a result, the reductive amination of carbonyl compounds with amines by photoredox catalysis proceeds in good to excellent yields and with broad substrate scope and good functional group tolerance. The three key features of this work are 1) the rapid interception of electron-rich α-aminoalkyl radical intermediates by polarity-matched HAT in a photoredox reaction, 2) the method of reductive amination by photoredox catalysis itself, and 3) the application of this new method for temporally and spatially controlled reactions on a solid support, as demonstrated by the attachment of a fluorescent dye on an activated cellulose support by photoredox-catalyzed reductive amination.

Visible light-promoted umpolung coupling of aryl tri-/difluoroethanones with 2-alkenylpyridines

A metal-free, mild, and simple protocol is developed for the synthesis of tertiary alcohols bearing tri-/difluoromethyl groups upon visible-light irradiation.

Regioselective C–H and N–H functionalization of purine derivatives and analogues: a synthetic and mechanistic perspective

This perspective provides a systematic and concise overview of the recent development in C–H/N–H bond functionalization in purine derivatives and analogues.

Copper-catalyzed selective radical–radical cross-coupling for C–S bond formation: an access to α-alkylthionitriles

Oxidative radical–radical cross-coupling: a new protocol for C–S bond formation was developed by selective cross-coupling between a thiyl radical and an isobutyronitrile radical.

Photo-induced, Cu-catalyzed three component azidofluoroalkylation of alkenes with CF3I and RfI as fluoroalkylation reagents

Under UV light irradiation, the Cu-catalyzed azidofluoroalkylation of alkenes was realized by directly using fluoroalkyl iodides as fluoroalkylation reagents.

A visible-light photocatalytic thiolation of aryl, heteroaryl and vinyl iodides

A method for the light-driven synthesis of aryl and vinyl alkyl thioethers from a range of C(sp²)–I bonds is reported.

Direct Activation of β-sp3-Carbons of Saturated Carboxylic Esters as Electrophilic Carbons via Oxidative Carbene Catalysis

An N-heterocyclic carbene-catalyzed oxidative LUMO activation of the β-cabons of saturated carboxylic esters is disclosed. This approach allows for efficient asymmetric access to lactams and lactones by directly installing functional groups to the typically inert β-sp³ carbons of saturated esters. The use of HOBt as an additive was found to significantly improve both yields and enantioselectivities of the reactions.

Recent developments in transition-metal photoredox-catalysed reactions of carbonyl derivatives

Single-electron reduction of C[double bond, length as m-dash]O and C[double bond, length as m-dash]N bonds of aldehydes, ketones, and imines results in the formation of ketyl and α-aminoalkyl anion radicals, respectively. These reactive intermediates are characterized by an altered electronic character with respect to their parent molecules and undergo a diverse range of synthetically useful transformations, which are not available to even-electron species. This Review summarizes the reactions of ketyl and α-aminyl radicals generated from carbonyl derivatives under transition-metal photoredox-catalysed conditions. We primarily focus on recent developments in the field, as well as give a brief overview of catalytic enantioselective transformations that provide a means to achieve precise stereocontrol over the reactivity of ion radicals.

Photoinduced, Copper-Promoted Regio- and Stereoselective Decarboxylative Alkylation of α,β-Unsaturated Acids with Alkyl Iodides

The first example of UV light-induced, copper-catalyzed regio- and stereoselective decarboxylative coupling of α,β-unsaturated acids with alkyl iodides was reported. Under standard conditions, the 1°, 2°, and 3° alkyl iodides proceeded smoothly with the E-selective alkenes obtained in uniformly good yields and high stereoselectivities.

Allyl-Palladium-Catalyzed Ketone Dehydrogenation Enables Telescoping with Enone α,β-Vicinal Difunctionalization

The telescoping of allyl-palladium catalyzed ketone dehydrogenation with organocuprate conjugate addition chemistry allows for the introduction of aryl, heteroaryl, vinyl, acyl, methyl, and other functionalized alkyl groups chemoselectively to a wide variety of unactivated ketone compounds via their enone counterparts. The compatibility of the dehydrogenation conditions additionally allows for efficient trapping of the intermediate enolate with various electrophiles. The utility of this approach is demonstrated by comparison to several previously reported multistep sequences.