Allylic Amination of Alkenes with Iminothianthrenes to Afford Alkyl Allylamines

Selenium-catalyzed allylic C-H phosphoramidation of alkenes

We report herein a synthesis of allylic phosphoramidates from alkenes by selenium-catalyzed allylic C-H derivatization. This method features mild conditions, broad substrate scope, and high functional group tolerance, enabling late-stage modification of a number of complex substrates. In addition, this protocol was applied to modify caryophyllene and produced a photoaffinity probe capable of proteomic target labeling in live HeLa cells.

Photoinduced Regioselective Fluorination and Vinylation of Remote C(sp3)-H Bonds Using Thianthrenium Salts

Herein, a photoredox-driven practical protocol for fluorinated alkene synthesis using easily accessible and modular thianthrenium salts with electron-withdrawing alkynes or propargyl alcohols is reported. Vinyl radical intermediates, formed by the reaction between the alkyl or trifluoromethyl thianthrenium salts and electronically diverse alkynes, can mediate the key 1,5-HAT process of regioselective C(sp3)-H fluorination and vinylation. This protocol provides straightforward access to structurally diverse trifluoromethyl- or distally fluoro-functionalized alkene products in 21-79% yields with a broad substrate range under mild photocatalytic conditions.

Alkene Thianthrenation Unlocks Diverse Cation Synthons: Recent Progress and New Opportunities

Oxidative alkene functionalization reactions are a fundamental class of complexity-building organic transformations. However, the majority of established approaches rely on electrophilic reagents that limit the diversity of groups that can be installed. Recent advances have established a new approach that instead relies on the transformation of alkenes into thianthrene-derived cationic electrophiles. These linchpin intermediates can be generated selectively and undergo a diverse array of mechanistically distinct reactions with abundant nucleophiles. Taken together, this unlocks a suite of net oxidative alkene transformations that have been elusive using conventional strategies. This Minireview describes these advances and is organized around the three distinct synthons formally accessible from alkenes via thianthrenation: 1) alkenyl cations; 2) vicinal dications; 3) allyl cations. Throughout the Minireview, we illustrate how thianthrenium salts address key limitations endemic to classic alkene-derived electrophiles and highlight the mechanistic origins of these distinctions wherever possible.

Direct synthesis of branched amines enabled by dual-catalyzed allylic C─H amination of alkenes with amines

Direct conversion of hydrocarbons into amines represents an important and atom-economic goal in chemistry for decades. However, intermolecular cross-coupling of terminal alkenes with amines to form branched amines remains extremely challenging. Here, a visible-light and Co-dual catalyzed direct allylic C─H amination of alkenes with free amines to afford branched amines has been developed. Notably, challenging aliphatic amines with strong coordinating effect can be directly used as C─N coupling partner to couple with allylic C─H bond to form advanced amines with molecular complexity. Moreover, the reaction proceeds with exclusive regio- and chemoselectivity at more steric hinder position to deliver primary, secondary, and tertiary aliphatic amines with diverse substitution patterns that are difficult to access otherwise.

Desulfurative Functionalization of β-Acyl Allylic Sulfides with N-H Free Indoles Highly Regioselective at C3 and N1 Positions: Rapid Access to α-Branched Enones

A regiodivergent allylation of 1H-indoles highly selectively at the C3 and N1 positions with β-acyl allylic sulfides through desulfurative C-C/C-N bond-forming reactions has been developed under mild conditions. Notably, the remarkable site-selective switch can be achieved by a delicate choice of solvents and bases. This cost-efficient method displays a broad substrate scope, good functional compatibility, and excellent site-selectivity, thus offering a divergent synthesis of indole substituted α-branched enones, which possess diverse potential opportunities for further applications and derivatization.

1,4-Aminoarylation of Butadienes via Photoinduced Palladium Catalysis

A visible-light-induced, three-component palladium-catalyzed 1,4-aminoarylation of butadienes with readily available aryl halides and aliphatic amines has been developed, affording allylamines with excellent E-selectivity. The reaction exhibits exceptional control over chemo-, regio-, and stereoselectivity, a broad substrate scope, and high functional group compatibility, as demonstrated by the late-stage functionalization of bioactive molecules. Mechanistic investigations are consistent with a photoinduced radical Pd(0)-Pd(I)-Pd(II)-Pd(0) Heck-Tsuji-Trost allylation cascade.

Cobalt-Catalyzed Carbon-Heteroatom Transfer Enables Regioselective Tricomponent 1,4-Carboamination

Tricomponent cobalt(salen)-catalyzed carbofunctionalization of unsaturated substrates by radical-polar crossover has the potential to streamline access to broad classes of heteroatom-functionalized synthetic targets, yet the reaction platform has remained elusive, despite the well-developed analogous hydrofunctionalizations mediated by high-valent alkylcobalt intermediates. We report herein the development of a cobalt(salen) catalytic system that enables carbofunctionalization. The reaction entails a tricomponent decarboxylative 1,4-carboamination of dienes and provides a direct route to aromatic allylic amines by obviating preformed allylation reagents and protection of oxidation-sensitive aromatic amines. The catalytic system merges acridine photocatalysis with cobalt(salen)-catalyzed regioselective 1,4-carbofunctionalization that facilitates the crossover of the radical and polar phases of the tricomponent coupling process, revealing critical roles of the reactants, as well as ligand effects and the nature of the formal high-valent alkylcobalt species on the chemo- and regioselectivity.

Multiple-cycle photochemical cascade reactions

Cascade reactions represent an efficient and economical synthetic approach, enabling the rapid synthesis of a wide array of structurally complex organic compounds. These compounds, previously inaccessible, can now be synthesized in a remarkably limited number of steps. Concurrently, the photochemical reactions of organic molecules have gained prominence as a potent strategy for accessing a diverse range of radical species and intermediates. This is achieved in a controlled manner under mild conditions. Owing to the relentless endeavors of chemists, significant strides have been made in the realm of photochemical cascade reactions. These advancements have facilitated the synthesis of novel molecular structures with high complexity, structures that are typically challenging to generate under thermal conditions. In this review, we comprehensively summarize and underscore the recent pivotal advancements in visible-light-induced cascade reactions. Our focus is on the elucidation of multiple photochemical catalytic cycles, emphasizing the catalytic activation modes and the types of reactions involved.

Iridium-catalysed reductive allylic amination of α,β-unsaturated aldehydes

Allylic amination is a powerful tool for constructing N-allylic amines widely found in bioactive molecules. Generally, allylic alcohols and unsaturated hydrocarbons have been considered for allylic amination reactions to minimize waste production. Herein, we present an iridium-catalysed method for reductive allylic amination of α,β-unsaturated aldehydes with amines to afford N-allylic amines under air conditions. This protocol is demonstrated to provide products from many substrates (41 examples) in moderate-to-excellent yields. This synthetic methodology is also highlighted by the synthesis of drug molecules, optically pure products, as well as scale-up experiments.

Chemo-divergent Cyano Group Migration: Involving Elimination and Substitution of the Key α-Thianthrenium Cyano Species

Herein, we report a light-driven, radical-type cyano migration in the absence of a photocatalyst, enabling a chemo-divergent synthesis of (Z)-alkenyl nitriles and ketones. Trifluoromethyl thianthrenium salt (TT-CF3+OTf-) plays multiple roles: (a) absorbing light to generate trifluoromethyl radicals to initiate the reaction and (b) forming α-thianthrenium cyano species by in situ capture of TT• +. (Z)-Alkenyl nitriles were formed through the elimination of thianthrenium salts, and aryl ketones were obtained via the nucleophilic substitution of thianthrenium salts.

Merging of Light/Dark Palladium Catalytic Cycles Enables Multicomponent Tandem Alkyl Heck/Tsuji-Trost Homologative Amination Reaction toward Allylic Amines

A visible light-induced palladium-catalyzed homologative three-component synthesis of allylic amines has been developed. This protocol proceeds via a unique mechanism involving two distinct cycles enabled by the same Pd(0) catalyst: a visible light-induced hybrid radical alkyl Heck reaction between 1,1-dielectrophile and styrene, followed by the "in dark" classical Tsuji-Trost-type allylic substitution reaction. This method works well with a broad range of primary and secondary amines, aryl alkenes, dielectrophiles, and in complex settings. The regiochemistry of the obtained products is primarily governed by the structure of 1,1-dielectrophile. Involvement of π-allyl palladium intermediates allowed for the control of stereoselectivity, which has been demonstrated with up to 95:5 er.

Nickel Meets Aryl Thianthrenium Salts: Ni(I)-Catalyzed Halogenation of Arenes

Herein, a regioselective, late-stage two-step arene halogenation method is reported. We propose how unusual Ni(I)/(III) catalysis is enabled by a combination of aryl thianthrenium and Ni redox properties that is hitherto unachieved with other (pseudo)halides. The catalyst is accessed in situ from inexpensive NiCl₂·6(H₂O) and zinc without the need of supporting ligands.

Palladium-Catalyzed Oxidative Amination of Unactivated Olefins with Primary Aliphatic Amines

Direct coupling of unactivated olefins with primary alkylamines is considered to be an efficient but unknown method for the construction of complex amines. Herein we report a catalytic intermolecular oxidative amination of unactivated olefins with primary aliphatic amines based on the combination of a palladium catalyst, a bidentate phosphine ligand, and duroquinone. A range of secondary allylic amines were obtained in good yields with excellent regio- and stereoselectivity. Mechanistic control experiments revealed that the reaction proceeds by allylic C(sp³)-H activation and nucleophilic amination. The utility of the protocol is further demonstrated with the late-stage modification and streamlined synthesis of drug molecules.

Metalloradical approach for concurrent control in intermolecular radical allylic C-H amination

Although they offer great potentials, the high reactivity and diverse pathways of radical chemistry pose difficult problems for applications in organic synthesis. In addition to the differentiation of multiple competing pathways, the control of various selectivities in radical reactions presents both formidable challenges and great opportunities. To regulate chemoselectivity and regioselectivity, as well as diastereoselectivity and enantioselectivity, calls for the formulation of conceptually new approaches and fundamentally different governing principles. Here we show that Co(II)-based metalloradical catalysis enables the radical chemoselective intermolecular amination of allylic C-H bonds through the employment of modularly designed D2-symmetric chiral amidoporphyrins with a tunable pocket-like environment as the supporting ligand. The reaction exhibits a remarkable convergence of regioselectivity, diastereoselectivity and enantioselectivity in a single catalytic operation. In addition to demonstrating the unique opportunities of metalloradical catalysis in controlling homolytic radical reactions, the Co(II)-catalysed convergent C-H amination offers a route to synthesize valuable chiral α-tertiary amines directly from an isomeric mixture of alkenes.

Synthesis of Sulfilimines via Selective S-C Bond Formation in Water

Sulfilimines are valuable compounds both in organic synthesis and in pharmaceuticals. Here we developed a mild and simplified method for preparation of sulfilimines via selective S-C bond formation rather than traditional S-N bond formation. The method is both attractive and useful for the following reasons: it uses a readily available alkylation reagent such alkyl bromide or alkyl iodide, it uses water as solvent, it is easy to perform, and it is convenient for late-stage diversification of drugs.

Palladium-Catalyzed Branch- and Z-Selective Allylic C-H Amination with Aromatic Amines

Allylamines are important building blocks in the synthesis of bioactive compounds. The direct coupling of allylic C-H bonds and commonly available amines is a major synthetic challenge. An allylic C-H amination of 1,4-dienes has been accomplished by palladium catalysis. With aromatic amines, branch-selective allylic aminations are favored to generate thermodynamically unstable Z-allylamines. In addition, more basic aliphatic cyclic amines can also engage in the reaction, but linear dienyl allylic amines are the major products.

Asymmetric intermolecular allylic C-H amination of alkenes with aliphatic amines

Aliphatic allylic amines are found in a great variety of complex and biorelevant molecules. The direct allylic C-H amination of alkenes serves as the most straightforward method toward these motifs. However, use of widely available internal alkenes with aliphatic amines in this transformation remains a synthetic challenge. In particular, palladium catalysis faces the twin challenges of inefficient coordination of Pd(II) to internal alkenes but excessively tight and therefore inhibitory coordination of Pd(II) by basic aliphatic amines. We report a general solution to these problems. The developed protocol, in contrast to a classical Pd(II/0) scenario, operates through a blue light-induced Pd(0/I/II) manifold with mild aryl bromide oxidant. This open-shell approach also enables enantio- and diastereoselective allylic C-H amination.

Organothianthrenium salts: synthesis and utilization

Organothianthrenium salts are a class of compounds containing a positively charged sulfur atom and a neutral sulfur atom. Over the past years, organothianthrenium salts have been emerging as attractive precursors for a myriad of transformations to forge new C-C and C-X bonds due to their unique structural characteristics and chemical behaviors. The use of the thianthrenation strategy selectively transforms C-H, C-O, and other chemical bonds into organothianthrenium salts in a predictable manner, providing a straightforward alternative for regioselective functionalizations for arenes, alkenes, alkanes, alcohols, amines and so on through diverse reaction mechanisms under mild conditions. In this review, the preparation of different organothianthrenium salts is summarized, including aryl, alkenyl and alkyl thianthrenium salts. Moreover, the utilization of organothianthrenium salts in different catalytic processes and their synthetic potentials are also discussed.

Cascade cyclization of alkene-tethered acylsilanes and allylic sulfones enabled by unproductive energy transfer photocatalysis

Developing photo-induced cascade cyclization of alkene-tethered acylsilanes is challenging, because acylsilanes are unstable under light irradiation. Herein, we report that the energy transfer from excited acylsilanes to a photocatalyst that possesses lower triplet energy can inhibit the undesired decomposition of acylsilanes. With neutral Eosin Y as the photocatalyst, an efficient synthesis of cyclopentanol derivatives is achieved with alkene-tethered acylsilanes and allylic sulfones. The reaction shows broad substrate scope and the synthetic potential of this transformation is highlighted by the construction of cyclopentanol derivatives which contain fused-ring or bridged-ring.

Acylsilanes decompose under light irradiation, and this limits their use in light-induced organic transformations. Here the authors report a strategy to inhibit the light-induced decomposition of acylsilanes, enabling the photochemical synthesis of cyclopentanol derivatives from alkene-tethered acylsilanes and allylic sulfones.

Hydroamination of Unactivated Alkenes with Aliphatic Azides

We report here an efficient and highly diastereoselective intermolecular anti-Markovnikov hydroamination of unactivated alkenes with aliphatic azides in the presence of silane. The system tolerates a wide range of azides and alkenes and operates with alkene as limiting reagent. Mechanistic studies suggest a radical chain pathway that involves aminium radical formation, radical addition to alkenes and HAT from silane to β-aminium alkyl radical. The use of sterically bulky silane is proposed to contribute to the excellent diastereoselectivity for HAT. Computational analysis uncovers the reaction pathway of aliphatic azide activation with silyl radical for aminyl radical formation.

Palladium-catalysed selective oxidative amination of olefins with Lewis basic amines

Amines are prominent in natural products, pharmaceutical agents and agrochemicals. Moreover, they are synthetically valuable building blocks for the construction of complex organic molecules and functional materials. However, amines, especially aliphatic and aromatic amines with free N-H bonds, tend to coordinate with transition metals and deactivate the catalyst, posing a tremendous challenge to applying Lewis basic amines in the amination of olefins. Here we present an example of oxidative amination of simple olefins with various Lewis basic amines. The combination of a palladium catalyst, 2,6-dimethyl-1,4-benzoquinone and a phosphorous ligand leads to the efficient synthesis of alkyl and aryl allylamines. A series of allylamines were obtained with good yields and excellent regio- and stereoselectivities. Intramolecular amination to synthesize tetrahydropyrrole and piperidine derivatives was also realized. Mechanistic investigations reveal that the reaction undergoes allylic C(sp³)-H activation and subsequent functionalization.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Photo-catalyzed acetoxysulfoximination of styrene with sulfoximidoyl thianthrenium salt

We report the design and synthesis of a redox-active thianthrenium-containing sulfoximination reagent. Photo-catalyzed acetoxysulfoximination of styrene with various functional groups is described. Preliminary mechanistic studies indicated that the sulfoximination reagent (2aa) received a single electron transfer (SET) from the photo-excited Ir(ppy)₃ catalyst to produce a sulfoximidoyl radical as a key intermediate in this transformation.

Bifunctional sulfilimines enable synthesis of multiple N-heterocycles from alkenes

Intramolecular cyclization of nitrogen-containing molecules onto pendant alkenes is an efficient strategy for the construction of N-heterocycles, which are of paramount importance in, for example, pharmaceuticals and materials. Similar intermolecular cyclization reactions, however, are scarcer for nitrogen building blocks, including N-centred radicals, and divergent and modular versions are not established. Here we report the use of sulfilimines as bifunctional N-radical precursors for cyclization reactions with alkenes to produce N-unprotected heterocycles in a single step through photoredox catalysis. Structurally diverse sulfilimines can be synthesized in a single step, and subsequently engage with alkenes to afford synthetically valuable five-, six- and seven-membered heterocycles. The broad and diverse scope is achievable by a radical-polar crossover annulation enabled by the bifunctional character of the reagents, which distinguishes itself from all other N-centred-radical-based reactions. The modular synthesis of the sulfilimines allows for larger structural diversity of N-heterocycle products than is currently achievable with other single cyclization methods.

Intermolecular cyclization reactions using nitrogen-containing building blocks are scarce. Now, bifunctional sulfilimines have been shown to enable the modular construction of a diverse range of N-heterocycles by reacting with alkenes in a single photocatalysed step. Both sulfilimines and alkenes are easily accessible, providing access to a wide range of N-heterocycles with different ring types, ring sizes and substituents on the skeleton.

Recent advances in visible light-induced C(sp3)–N bond formation

Synthetic chemists have long focused on selective C(sp ³)-N bond-forming approaches in response to the high value of this motif in natural products, pharmaceutical agents and functional materials. In recent years, visible light-induced protocols have become an important synthetic platform to promote this transformation under mild reaction conditions. These photo-driven methods rely on converting visible light into chemical energy to generate reactive but controllable radical species. This Review highlights recent advances in this area, mostly after 2014, with an emphasis placed on C(sp ³)-H bond activations, including amination of olefins and carbonyl compounds, and cross-coupling reactions.

Visible-light-catalyzed C-H arylation of (hetero)arenes via arylselenonium salts

A novel photo-induced C-H arylation of (hetero)arenes has been developed. Aryl selenonium salts as an aryl source led to the arylation of aromatic (hetero)cyclic compounds via C-Se bond activation under blue LED irradiation. The method simply utilizes the safe and clean energy source and yields a range of site-selective biphenyl or bi-heterocyclic products in medium to good yields. Furthermore, the borylation and Sonogashira coupling of aryl selenonium salts proceed in good yields as well. From the results, it is shown that selenonium salts are more reactive than sulfonium salts.

Visible-Light-Induced Organocatalyzed [2+1] Cyclization of Alkynes and Trifluoroacetylsilanes

The synthesis of common cyclopropenes has been widely studied, but the synthesis of cyclopropenols is a significant challenge. Herein, we highlight our recent work on the synthesis of trifluoromethylated cyclopropenols through [2+1] cycloaddition reaction between alkynes and trifluoroacetylsilanes under visible-light-induced organocatalysis. The novel amphiphilic donor-acceptor carbenes derived from trifluoroacetylsilanes can react effectively with both activated and unactivated alkynes. Broad substrate scope and good functional group tolerance have been achieved. Besides, the synthetic potential of this reaction was highlighted by a gram-scale reaction and the one-pot diastereoselective synthesis of trifluoromethylated cyclopropanols.

Allylic C-H amination cross-coupling furnishes tertiary amines by electrophilic metal catalysis

Intermolecular cross-coupling of terminal olefins with secondary amines to form complex tertiary amines-a common motif in pharmaceuticals-remains a major challenge in chemical synthesis. Basic amine nucleophiles in nondirected, electrophilic metal-catalyzed aminations tend to bind to and thereby inhibit metal catalysts. We reasoned that an autoregulatory mechanism coupling the release of amine nucleophiles with catalyst turnover could enable functionalization without inhibiting metal-mediated heterolytic carbon-hydrogen cleavage. Here, we report a palladium(II)-catalyzed allylic carbon-hydrogen amination cross-coupling using this strategy, featuring 48 cyclic and acyclic secondary amines (10 pharmaceutically relevant cores) and 34 terminal olefins (bearing electrophilic functionality) to furnish 81 tertiary allylic amines, including 12 drug compounds and 10 complex drug derivatives, with excellent regio- and stereoselectivity (>20:1 linear:branched, >20:1 E:Z).

Synthesis of Cyclopropenols Enabled by Visible-Light-Induced Organocatalyzed [2+1] Cyclization

Although the synthesis of common cyclopropenes has been well studied, the access to cyclopropenols is rather limited. Herein, we report the first synthesis of α-trifluoromethylated cyclopropenols via 2+1 cycloaddition reactions between alkynes and trifluoroacylsilanes, enabled by visible-light-induced organocatalysis. The novel ambiphilic donor-acceptor carbenes derived from trifluoroacetylsilanes reacted efficiently with both activated and non-activated alkynes. The reaction features simple operation, mild conditions, broad substrate scope and good functional group tolerance. The synthetic potential of the reaction is highlighted by the gram-scale reactions and first synthesis of α-trifluoromethylated cyclopropanols through the combination of the 2+1 cyclization and high diastereoselective hydrogenation reaction in one pot.

Metal-free allylic C-H nitrogenation, oxygenation, and carbonation of alkenes by thianthrenation

Selective functionalization of allylic C–H bonds into other chemical bonds is among the most straightforward and attractive, yet challenging transformations. Herein, a transition-metal-free protocol for direct allylic C–H nitrogenation, oxygenation, and carbonation of alkenes by thianthrenation was developed. This operationally simple protocol allows for the unified allylic C–H amination, esterification, etherification, and arylation of vinyl thianthrenium salts. Notably, the reaction furnishes multialkyl substituted allylic amines, ammonium salts, sulfonyl amides, esters, and ethers in good yields. The reaction proceeds under mild conditions with excellent functional group tolerance and could be applied to late-stage allylation of natural products, drug molecules and peptides with excellent chemoselectivity.

Diverse functionalizations of allylic C–H bonds of alkenes by thianthrenation have been demonstrated, featuring Z-selectivity to afford multi-alkyl substituted allylic esters, thioesters, ethers, amines, amides and arenes under metal-free conditions.

Photoredox/Persistent Radical Cation Dual Catalysis for Alkoxy Radical Generation from Alcohols

In this report, we present a mild and general strategy for the direct generation of alkoxy radical from simple aliphatic alcohols enabled by visible-light-induced photoredox/persistent radical cation dual catalysis. The...

Intermolecular dearomative [4 + 2] cycloaddition of naphthalenes via visible-light energy-transfer-catalysis

The dearomative cycloaddition reaction serves as a blueprint for creating sp³-rich three-dimensional molecular topology from flat-aromatic compounds. However, severe reactivity and selectivity issues make this process arduous. Herein, we describe visible-light energy-transfer catalysis for the intermolecular dearomative [4 + 2] cycloaddition reaction of feedstock naphthalene molecules with vinyl benzenes. Tolerating a wide range of functional groups, structurally diverse 2-acyl naphthalenes and styrenes could easily be converted to a diverse range of bicyclo[2.2.2]octa-2,5-diene scaffolds in high yields and moderate endo-selectivities. The late-stage modification of the derivatives of pharmaceutical agents further demonstrated the broad potentiality of this methodology. The efficacy of the introduced methods was further highlighted by the post-synthetic diversification of the products. Furthermore, photoluminescence, electrochemical, kinetic, control experiments, and density-functional theory calculations support energy-transfer catalysis.

Constructing 3D molecular scaffolds from aromatic hydrocarbons is challenging. Herein, we report dearomative [4 + 2] cycloaddition reaction of naphthalenes via visible-light EnT catalysis which overcomes issues of unfavorable thermodynamics, low yields, and selectivity.

Electrochemical Synthesis of Allylic Amines from Terminal Alkenes and Secondary Amines

Allylic amines are valuable synthetic targets en route to diverse biologically active amine products. Current allylic C-H amination strategies remain limited with respect to the viable N-substituents. Herein, we disclose a new electrochemical process to prepare aliphatic allylic amines by coupling two abundant starting materials: secondary amines and unactivated alkenes. This oxidative transformation proceeds via electrochemical generation of an electrophilic adduct between thianthrene and the alkene substrates. Treatment of these adducts with aliphatic amine nucleophiles and base provides allylic amine products in high yield. This synthetic strategy is also amenable to functionalization of feedstock gaseous alkenes at 1 atm. In the case of 1-butene, high Z-selective crotylation is observed. This strategy, however, is not limited to the synthesis of simple building blocks; complex biologically active molecules are suitable as both alkene and amine coupling partners. Preliminary mechanistic studies implicate vinylthianthrenium salts as key reactive intermediates.

Direct Synthesis of Allyl Amines with 2-Nitrosulfonamide Derivatives via the Tsuji-Trost Reaction

The Tsuji-Trost Reaction is a palladium-catalysed allylation of nucleophiles that consists in the reaction of a nitrogen, carbon or oxygen-based nucleophiles with an allylic substrate bearing a leaving group. Here we present the use of 2-nitrosulfonamide derivatives as nucleophile, which are reactive under mild conditions. 2-nitrosulfonyl groups are well-known dual protective activator groups easy to introduce in any type of amine substrates. The resulting 2-nitrosulfonamide derivatives are ideal substrates for the Tsuji-Trost reaction to afford a convenient and flexible access to primary and dissymmetric secondary allyl amines. The optimised procedure is flexible (for solvent, temperature, functional groups) and has been applied with good to excellent yield to access to a wide range of allyl amine derivatives.

Late-Stage Intermolecular Allylic C-H Amination

Allylic amination enables late-stage functionalization of natural products where allylic C-H bonds are abundant and introduction of nitrogen may alter biological profiles. Despite advances, intermolecular allylic amination remains a challenging problem due to reactivity and selectivity issues that often mandate excess substrate, furnish product mixtures, and render important classes of olefins (for example, functionalized cyclic) not viable substrates. Here we report that a sustainable manganese perchlorophthalocyanine catalyst, [MnIII(ClPc)], achieves selective, preparative intermolecular allylic C-H amination of 32 cyclic and linear compounds, including ones housing basic amines and competing sites for allylic, ethereal, and benzylic amination. Mechanistic studies support that the high selectivity of [MnIII(ClPc)] may be attributed to its electrophilic, bulky nature and stepwise amination mechanism. Late-stage amination is demonstrated on five distinct classes of natural products, generally with >20:1 site-, regio-, and diastereoselectivity.

Advances in the E → Z Isomerization of Alkenes Using Small Molecule Photocatalysts

Geometrical E → Z alkene isomerization is intimately entwined in the historical fabric of organic photochemistry and is enjoying a renaissance (Roth et al. Angew. Chem., Int. Ed. Engl. 1989 28, 1193-1207). This is a consequence of the fundamental stereochemical importance of Z-alkenes, juxtaposed with frustrations in thermal reactivity that are rooted in microscopic reversibility. Accessing excited state reactivity paradigms allow this latter obstacle to be circumnavigated by exploiting subtle differences in the photophysical behavior of the substrate and product chromophores: this provides a molecular basis for directionality. While direct irradiation is operationally simple, photosensitization via selective energy transfer enables augmentation of the alkene repertoire to include substrates that are not directly excited by photons. Through sustained innovation, an impressive portfolio of tailored small molecule catalysts with a range of triplet energies are now widely available to facilitate contra-thermodynamic and thermo-neutral isomerization reactions to generate Z-alkene fragments. This review is intended to serve as a practical guide covering the geometric isomerization of alkenes enabled by energy transfer catalysis from 2000 to 2020, and as a logical sequel to the excellent treatment by Dugave and Demange (Chem. Rev. 2003 103, 2475-2532). The mechanistic foundations underpinning isomerization selectivity are discussed together with induction models and rationales to explain the counterintuitive directionality of these processes in which very small energy differences distinguish substrate from product. Implications for subsequent stereospecific transformations, application in total synthesis, regioselective polyene isomerization, and spatiotemporal control of pre-existing alkene configuration in a broader sense are discussed.

Synthesis of medicinally relevant oxalylamines via copper/Lewis acid synergistic catalysis

Allylamines have long been recognized as valuable synthons because of their excellent reactivity in organic synthesis. Here, an efficient amination reaction of allenyl ethers via copper/Lewis acid synergistic catalysis has been established, providing straightforward access to diverse functionalized Z-oxalylamines and E -halogenated oxalylamines in good to excellent yields with high regio- and stereoselectivities. The developed method tolerates more than 100 examples that include late-stage functionalization of bioactive molecules, and features gram-scale synthesis of oxalylamines with high turnover number (TON > 1000) under mild and simple conditions. The applicability of the protocol is further demonstrated with the construction of drug molecules.

N-Methyl Allylic Amines from Allylic Alcohols by Mitsunobu Substitution Using N-Boc Ethyl Oxamate

We report the practical, scalable synthesis of a range of N-methyl allylic amines. Primary and secondary allylic alcohols underwent a regioselective Mitsunobu reaction with readily accessible N-Boc ethyl oxamate to deliver the corresponding N-Boc allylic amines, including in enantiopure form via stereospecific substitution. Subsequent N-methylation and Boc deprotection without chromatography yielded the amine products as hydrochloride salts. This method solves the problem of converting commercially available alcohols into often volatile N-methyl allylic amines, many of which have limited commercial availability.

Electro-oxidative Intermolecular Allylic C(sp3)-H Aminations

The oxidative intermolecular nitrogenation of C(sp³)-H bonds represents one of the most straightforward strategies to construct nitrogen-containing molecules. However, a sacrificial chemical oxidant is generally required. Herein, we describe electrochemical oxidative intermolecular allylic C(sp³)-H aminations in an undivided cell by electric current. The cross-dehydrogenative amination proceeded efficiently with ample scope under metal- and chemical oxidant-free reaction conditions, giving molecular H₂ as the only byproduct.

Trifluoromethyl Thianthrenium Triflate: A Readily Available Trifluoromethylating Reagent with Formal CF3+, CF3•, and CF3- Reactivity

Here we report the synthesis and application of trifluoromethyl thianthrenium triflate (TT-CF₃⁺OTf^–) as a novel trifluoromethylating reagent, which is conveniently accessible in a single step from thianthrene and triflic anhydride. We demonstrate the use of TT-CF₃⁺OTf^– in electrophilic, radical, and nucleophilic trifluoromethylation reactions.

Silver Salt-Mediated Allylation Reactions Using Allyl Bromides

A facile, efficient, and chemoselective synthesis of allylic amides has been developed. Allyl bromides were used as the precursors activated by silver triflate. A Ritter-type reaction readily proceeded to give various allyl amides under mild conditions. The reaction protocol was also applicable to different nucleophilic partners to give a wide range of allyl-substituted products in the absence of a base.