Catalyst-Free Visible-Light-Mediated Iodoamination of Olefins and Synthetic Applications

The Vicinal-Diiodination of the HDDA-Benzynes by N-Iodo- succinimide (NIS) Through a Radical Pathway

The 1,2-diradical reactivity of the HDDA-benzynes (thermal) has not been explored well in comparison to their ionic reactivity. Accordingly, the radical trapping reactions of these reactive intermediates are very scarce in literature. Herein, we report the iodine-radical trapping reaction of the HDDA-benzynes for the construction of structurally divergent vicinal-diiodo arenes. The N-iodosuccinimide (NIS) has been employed as the source of radical iodine under thermal heating conditions. The existence of the arene-radical intermediates and the radical mechanism has been supported by the EPR spectral analysis of the reaction mixture. Several fruitful control experiments suggested that the 4-iodination (mono-) of the HDDA-benzynes is faster than the 5-iodiniation. The process is general in terms of substituents on the diynes as well as the nature of the tethering units. To the best of our knowledge, this is the first report on the vicinal-diiodination as well as radical diiodination of HDDA-benzynes.

Harnessing light without photocatalysts: advances in photocatalyst-free C-N bond formation

The present feature article focuses on recent developments in the realm of photocatalyst-free C-N bond formations, highlighting the innovative approaches that leverage light without relying on traditional photocatalysts. Exploring alternative methodologies underscores the advancements in synthetic strategies, enabling efficient and sustainable C-N bond formation reactions. The abstracted review emphasizes the significant progress made in this field, shedding light on the potential for novel and environmentally friendly pathways for chemical synthesis.

Method and Mechanistic Insights to 1,2-Aminochlorinate Alkenes using Blue-Light Activated Dichlorocarbamates

Blue light activation of N,N-dichlorocarbamates facilitates a direct 1,2-aminochlorination of unactivated olefins to yield 1,2-chloro-N-Cl compounds under ambient conditions. Mechanistic studies suggest that N,N-dichlorocarbamates undergo a photochemical excitation to yield a neutral nitrogen-centered radical, which rapidly reacts with olefins in an anti-Markovnikov fashion. Using this method, a range of functionally diverse substrates are successfully aminochlorinated to yield the corresponding 1,2-chloro-N-Cl compounds.

Visible Light-Mediated Selective Synthesis of β-Amino Sulfide Scaffolds via Dual Role of N-Iodosuccinimide

The synthesis of β-amino sulfides is significant in organic chemistry. However, challenges such as achieving regioselectivity and the limited availability of starting materials remain unresolved. In this study, we present a visible light-mediated method for the selective synthesis of β-amino sulfide scaffolds. Remarkably, two distinct types of β-amino sulfides were selectively synthesized through the dual role of N-iodosuccinimide, which functions as either a reactant or an activator in the construction of the target scaffolds.

1,2-Acylphosphinylation of Styrenes to Access β-Aryl-γ-ketophosphine Oxides by Irradiation-Induced Radical Relay

An acylphosphinylation reaction has been devised for the synthesis of β-aryl-γ-ketophosphine oxides, employing styrenes and acyl azolium salts through an irradiation-induced radical relay mechanism. This method effectively constructs C-C and C-P bonds while demonstrating excellent functional group tolerance. Mechanistic studies revealed that a radical-addition-coupling-elimination cascade process was involved in this reaction.

A mild and scalable one-pot synthesis of N-substituted 2-aminobenzimidazoles via visible light mediated cyclodesulfurization

A visible light mediated photocatalyst-free synthesis of N-substituted 2-aminobenzimidazoles directly from o-phenylenediamines and isothiocyanates is developed in a one-pot fashion. This one-pot reaction proceeds through three steps: N-substitution of o-phenylenediamines, thiourea formation and visible light mediated cyclodesulfurization. This method enables the rapid and efficient synthesis of structurally diverse N-substituted 2-aminobenzimidazoles, achieving yields up to 92% across 69 examples. The practicality of the reaction is demonstrated by gram-scale synthesis. The key advantages of this method include the use of less toxic solvent in aqueous media, the elimination of photocatalyst, and a simple, practical setup (one-pot, open-flask, and ambient temperature). Mechanistic insights are gathered through control experiments, including light on/off cycles and radical inhibition studies. The results indicate that the reaction involves with radical pathway mediated by visible light.

Photoinduced C(sp3)-H Bicyclopentylation Enabled by an Electron Donor-Acceptor Complex-Mediated Chemoselective Three-Component Radical Relay

The photoredox electron donor-acceptor (EDA) complex-mediated radical coupling reaction has gained prominence in the field of organic synthesis, finding widespread application in two-component coupling reactions. However, EDA complex-promoted multi-component reactions are not well developed with only a limited number of examples have been reported. Herein, we report a photoinduced and EDA complex-promoted highly chemoselective three-component radical arylalkylation of [1.1.1]propellane, which allows the direct functionalization of C(sp3)-H with bicyclo[1.1.1]pentanes (BCP)-aryl groups under mild conditions. A variety of unnatural α-amino acids, featuring structurally diversified 1,3-disubstituted BCP moieties, were synthesized in a single-step process. Notably, leveraging the high tension release of [1.1.1]propellane, the highly unstable transient aryl radical undergoes rapid conversion into a relatively stable tertiary alkyl transient radical, and consequently, the competing side-reaction of two-component coupling was entirely suppressed. The strategic use of this transient radical conversion approach would be useful for the design of diverse EDA complex-mediated multi-component reactions. It is noteworthy that the highly chemoselective late-stage incorporation of the 1,3-disubstituted BCP pharmacophores into peptides was achieved both in liquid-phase and solid-phase reactions. This advancement is anticipated to have significant application potential in the future development of peptide drugs.

Metal-Free Synthesis of Pharmaceutically Relevant Sulfonylureas via Direct Reaction of Sulfonamides with Amides

A metal-free process has been developed for the sustainable synthesis of medicinally important sulfonylureas in one pot via the direct reaction of sulfonamides with amides in green solvent (DMC). The reaction proceeded efficiently at room temperature, and the products were obtained in good to excellent yields. The use of readily accessible, inexpensive, and environmentally benign starting materials and reagents, metal-free mild reaction conditions, wide substrate scope, tolerance to air and moisture, operational simplicity, and good atom economy are the salient features of this reaction protocol. Gram-scale synthesis of antidiabetic drugs tolbutamide and chlorpropamide in excellent yields further revealed the practical utility of this procedure. Additionally, the synthetic value of this straightforward method is showcased by the late-stage modification of drug molecules, including drug-drug conjugation with good yields. Preliminary mechanistic studies indicated the in situ generation of an isocyanate intermediate, which further reacts with sulfonamide to form sulfonylurea. As compared to other related methods reported for sulfonylurea synthesis, the current method obviates the requirement of traditional multistep protocols involving isolation of hazardous isocyanates and avoids the use of toxic phosgene.

Harnessing Bromo/Acyloxy Transposition (BrAcT) and Excited-State Copper Catalysis for Styrene Difunctionalization

1,2-Difunctionalization of styrenes, adding two distinct functional groups across the C═C double bond, has emerged as a powerful tool for enhancing molecular complexity. Herein, we report the development of a regioconvergent β-acyloxylation-α-ketonylation of styrenes through bromo/acyloxy transposition (BrAcT) and excited-state copper catalysis. This approach is amenable to gram-scale synthesis and tolerates a wide range of functional groups and complex molecular frameworks, including derivatives of natural products and marketed drugs. Our experimental and computational studies suggest a unique mechanism featuring a dynamic, ionic BrAcT process and excited-state copper-catalyzed redox reactions. We anticipate that this BrAcT process could serve as a broadly applicable and versatile strategy for β-acyloxylation-α-functionalization of styrenes, creating valuable intermediates for preparing new pharmaceuticals, agrochemicals, and functional materials.

Photo-induced imino functionalizations of alkenes via intermolecular charge transfer

A catalyst-free photosensitized strategy has been developed for regioselective imino functionalizations of alkenes via the formation of an EDA complex. This photo-induced protocol facilitates the construction of structurally diverse β-imino sulfones and vinyl sulfones in moderate to high yields. Mechanistic studies reveal that the reaction is initiated with an intermolecular charge transfer between oximes and sulfinates, followed by fragmentation to generate a persistent iminyl radical and transient sulfonyl radical. This catalyst-free protocol also features excellent regioselectivity, broad functional group tolerance and mild reaction conditions. The late stage functionalization of natural product derived compounds and total synthesis of some bioactive molecules have been demonstrated to highlight the utility of this protocol. Meanwhile, the compatibility of different donors has proved the generality of this strategy.

Handling fluorinated gases as solid reagents using metal-organic frameworks

Fluorine is an increasingly common substituent in pharmaceuticals and agrochemicals because it improves the bioavailability and metabolic stability of organic molecules. Fluorinated gases represent intuitive building blocks for the late-stage installation of fluorinated groups, but they are generally overlooked because they require the use of specialized equipment. We report a general strategy for handling fluorinated gases as benchtop-stable solid reagents using metal-organic frameworks (MOFs). Gas-MOF reagents are prepared on gram-scale and used to facilitate fluorovinylation and fluoroalkylation reactions. Encapsulation of gas-MOF reagents within wax enables stable storage on the benchtop and controlled release into solution upon sonication, which represents a safer alternative to handling the gas directly. Furthermore, our approach enables high-throughput reaction development with these gases.

Generation and Aerobic Oxidation of Azavinyl Captodative Radicals

We describe a cascade reaction that selectively incorporates oxygen into the carbon-carbon backbone of alkynes using air as the source. The process starts by lithiating readily available, electron-deficient 1,2,3-triazoles, resulting in an amphoteric lithium ketenimine intermediate. This intermediate can react with both electrophiles and nucleophiles. Under the conditions outlined in this study, we generate azavinyl radicals, which are a rare subset of captodative radicals. When exposed to atmospheric oxygen, these radicals efficiently transform into α-oxygenated amidines─a class of compounds that has not been extensively studied. This process uniquely utilizes molecular oxygen without requiring metal or photocatalysts, and it occurs under mild conditions. Our mechanistic studies provide insights into the intricate sequence involved in the formation and selective capture of azavinyl captodative radicals.

Photochemical Aminochlorination of Alkenes without the Use of an External Catalyst

The niche field of photochemistry offers opportunities that are not found in "traditional" ground state chemical pathways. Aminochlorinated derivatives are an interesting family of 1,2-difunctionalised compounds that provide access to a variety of natural products and pharmaceutical active substances. A practical, catalyst-free chloroamination protocol is described herein, providing access to intermediates of great importance, utilising mild and photochemical reaction conditions (370 nm), where N-chlorosulfonamides are used as both nitrogen and chlorine sources. A wide variety of olefins, decorated with a plethora of functional groups, was tested providing excellent results (28 examples, 18-88 % yield). Mechanistic studies (UV-Vis, control experiments and quantum yield measurement) were also performed.

Synthesis of Oxazolidines and Dihydroxazines via Cyclization of α-Aminated Ketones

A new approach to oxazolidines and dihydroxazines was developed by regioselective cyclization of α-aminated ketones under transition metal-free conditions. Oxazolidine derivatives were generated in the presence of chloro benziodoxole and TFA, while dihydroxazines were formed without a hypervalent iodine reagent. The reaction was performed under room temperature and gave the products in good to excellent yields.

Tunable [3+2] and [4+2] annulations for pyrrolidine and piperidine synthesis

N-heterocycles are privileged pharmaceutical scaffolds in drug discovery and development. We disclose here divergent intermolecular coupling strategies that can access diverse N-heterocycles directly from olefins. The radical-to-polar mechanistic switching is key for the divergent cyclization processes. These distinctive annulations result in the coupling of alkenes with simple bifunctional reagents for divergent N-heterocycle syntheses.

Regioselective and Diastereoselective Halofunctionalization of Alkenes Promoted by Organophotocatalytic Solar Catalysis

A visible-light metal-free photocatalytic regioselective and enantioselective alkene halofunctionalization reaction under mild conditions is reported. Various terminal and internal alkenes were transformed to their α-halogenated and α,β-dibrominated derivatives in good to excellent yields within reaction time as short as 5 min. Water can be used as the "green" nucleophile and solvent in the halohydroxylation and halo-oxidation reactions. Different types of products can be obtained by adjusting the reaction conditions. In addition, sunlight is proved to produce products with similar yields, representing a practical example of solar synthesis and providing an opportunity for solar energy utilization.

The advent of electrophilic hydroxylamine-derived reagents for the direct preparation of unprotected amines

Electrophilic aminating reagents have seen a renaissance in recent years as effective nitrogen sources for the synthesis of unprotected amino functionalities. Based on their reactivity, several noble and non-noble transition metal catalysed amination reactions have been developed. These include the aziridination and difunctionalisation of alkenes, the amination of arenes as well as the synthesis of aminated sulfur compounds. In particular, the use of hydroxylamine-derived (N-O) reagents, such as PONT (PivONH3OTf), has enabled the introduction of unprotected amino groups on various different feedstock compounds, such as alkenes, arenes and thiols. This strategy obviates undesired protecting-group manipulations and thus improves step efficiency and atom economy. Overall, this feature article gives a recent update on several reactions that have been unlocked by employing versatile hydroxylamine-derived aminating reagents, which facilitate the generation of unprotected primary, secondary and tertiary amino groups.

1,2-Amino oxygenation of alkenes with hydrogen evolution reaction

1,2-Amino oxygenation of alkenes has emerged as one of the most straightforward synthetic methods to produce β-amino alcohols, which are important organic building blocks. Thus, a practical synthetic strategy for 1,2-amino oxygenation is highly desirable. Here, we reported an electro-oxidative intermolecular 1,2-amino oxygenation of alkenes with hydrogen evolution, removing the requirement of extra-oxidant. Using commercial oxygen and nitrogen sources as starting materials, this method provides a cheap, scalable, and efficient route to a set of valuable β-amino alcohol derivatives. Moreover, the merit of this protocol has been exhibited by its broad substrate scope and good application in continuous-flow reactors. Furthermore, this method can be extended to other amino-functionalization of alkenes, thereby showing the potential to inspire advances in applications of electro-induced N-centered radicals (NCRs).

1,2-Aminoxygenation of alkenes without extra oxidant is a practical yet challenging way to prepare β-amino alcohols. Here, the authors report an electro-oxidative route achieving such a goal with H2 evolution, exhibiting broad scope and application potential.

Visible-light-mediated regioselective synthesis of novel thiazolo[3,2-b][1,2,4]triazoles: advantageous synthetic application of aqueous conditions

From a green chemistry perspective, sustainable irradiation as the power source and water as the solvent have certainly grabbed the attention of chemists in recent times because their use helps reduce the hazardous ecological footprints of organic synthesis. In the present work, we have established an efficient, straightforward and green protocol for the regioselective synthesis of novel functionalized thiazolo[3,2-b][1,2,4]triazoles. The visible-light-mediated catalyst-free reaction of diversely substituted α-bromodiketones, generated in situ by the reaction of NBS and 1,3-diketones, with 3-mercapto[1,2,4]triazoles under aqueous conditions afforded thiazolo[3,2-b][1,2,4]triazole derivatives in excellent yields. The structure of the regioisomer has been confirmed explicitly by heteronuclear 2D-NMR [(¹H-¹³C) HMBC, (¹H-¹³C) HMQC] spectroscopic and X-ray crystallographic studies. Radical initiating and trapping experiments supported the free radical mechanism for the cyclization.

Halogen bond promoted aryl migration of allylic alcohols under visible light irradiation

A simple and catalyst-free radical addition/1,2-aryl migration cascade process of ally alcohol driven by halogen bond was developed under visible light irradiation, featuring mild conditions, practical procedures, and broad substrate scope.