Photochemical Nitrene Transfer Reactions of Iminoiodinanes with Sulfides

Accessing Azetidines through Magnesium-Mediated Nitrogen Group Transfer from Iminoiodinane to Donor-Acceptor Cyclopropanes

Herein, we report a Lewis acid-mediated ring expansion of donor-acceptor cyclopropanes (DACs) to substituted azetidines via nucleophilic nitrogen group transfer from readily accessible iminoiodinane. This protocol operates under mild, transition-metal-free conditions, and showcases excellent chemoselectivity, along with broad functional group tolerance. We report for the first time that challenging alkyl donor-acceptor cyclopropanes can undergo ring expansion leading to aliphatic azetidines without relying on external oxidants or precious transition-metal catalysts. Mechanistically, the coordination of a magnesium (Mg)-Lewis acid to the DAC promotes nucleophilic ring opening with a putative Mg-amide species generated from the iminoiodinane under the reaction conditions to furnish the azetidine products.

Photolytic ortho-Selective Amino Pyridylation of Aryl Isocyanates with N-Amino Pyridinium Ylides for the Synthesis of N-Arylsulfonyl Ureas

Herein, we report an expedient synthesis of aryl sulfonyl ureas 4 and 5 from N-amino pyridinium ylides and aryl isocyanates. N-Aminopyridinium ylides 3 are synthesized via blue light-emitting diode irradiation of pyridine/isoquinoline and appropriate iminoiodinanes. The strategy involved a hitherto unknown carboamination of imine moieties (of aryl isocyanates) via a three-component reaction of pyridine derivatives/isoquinoline 1, N-aryl sulfonyl iminoiodinanes 2, and numerous aryl isocyanates at room temperature in 2-methyl tetrahydrofuran to afford the target compounds in moderate to excellent yields. N-Arylpyridinium ylides 3 (as intermediates) undergo a [3+2] cycloaddition with the aryl isocyanates followed by the aromatization of the pyridine/isoquinoline moiety to afford compounds 4. On the basis of the substitution pattern among the reactants, in some cases pyridine extrusion occurs during the reaction to afford depyridinylated aryl sulfonyl ureas 5. In general, isocyanates are used as dipolarophiles in [3+2] cycloaddition reactions. However, regioselective amino pyridylation of these species is a first. Control experiments and density functional theory calculations elucidate the reaction mechanism. The batch process of the protocol could be seamlessly transferred to the photoflow synthesis.

Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7-8 years, between 2016 and 2024.

Synthesis of Sulfilimines via Visible-Light-Mediated Triplet Energy Transfer to Sulfonyl Azides

Sulfilimines and their derivatives have garnered considerable interest in both synthetic and medicinal chemistry. Photochemical nitrene transfer to sulfides is known as a conventional synthetic approach to sulfilimines. However, the existing methods have a limited substrate scope stemming from the incompatibility of singlet nitrene intermediates with nucleophilic functional groups. Herein, we report the synthesis of N-sulfonyl sulfilimines via visible-light-mediated energy transfer to sulfonyl azides, uncovering the previously overlooked reactivity of triplet nitrenes with sulfides. This reaction features broad functional group tolerance, water compatibility, and amenability to the late-stage functionalization of drugs. Thus, this work represents an important example of energy transfer chemistry that overcomes challenges in traditional synthetic methods.

Visible photons as ideal reagents for the activation of coloured organic compounds

In recent decades, the traceless nature of visible photons has been exploited for the development of efficient synthetic strategies for the photoconversion of colourless compounds, namely, photocatalysis, chromophore activation, and the formation of an electron donor/acceptor (EDA) complex. However, the use of photoreactive coloured organic compounds is the optimal strategy to boost visible photons as ideal reagents in synthetic protocols. In view of such premises, the present review aims to provide its readership with a collection of recent photochemical strategies facilitated via direct light absorption by coloured molecules. The protocols have been classified and presented according to the nature of the intermediate/excited state achieved during the transformation.

Aziridination via Nitrogen-Atom Transfer to Olefins from Photoexcited Azoxy-Triazenes

Herein, we report that readily accessible azoxy-triazenes can serve as nitrogen atom sources under visible light excitation for the phthalimido-protected aziridination of alkenes. This approach eliminates the need for external oxidants, precious transition metals, and photocatalysts, marking a departure from conventional methods. The versatility of this transformation extends to the selective aziridination of both activated and unactivated multisubstituted alkenes of varying electronic profiles. Notably, this process avoids the formation of competing C-H insertion products. The described protocol is operationally simple, scalable, and adaptable to photoflow conditions. Mechanistic studies support the idea that the photofragmentation of azoxy-triazenes results in the generation of a free singlet nitrene. Furthermore, a mild photoredox-catalyzed N-N cleavage of the protecting group to furnish the free aziridines is reported. Our findings contribute to the advancement of sustainable and practical methodologies for the synthesis of nitrogen-containing compounds, showcasing the potential for broader applications in synthetic chemistry.

An unexpected synthesis of azepinone derivatives through a metal-free photochemical cascade reaction

Azepinone derivatives are privileged in organic synthesis and pharmaceuticals. Synthetic approaches to these frameworks are limited to complex substrates, strong bases, high power UV light or noble metal catalysis. We herein report a mild synthesis of azepinone derivatives by a photochemical generation of 2-aryloxyaryl nitrene, [2 + 1] annulation, ring expansion/water addition cascade reaction without using any metal catalyst. Among the different nitrene precursors tested, 2-aryloxyaryl azides performed best under blue light irradiation and Brønsted acid catalysis. The reaction scope is broad and the obtained products underwent divergent transformations to afford other related compounds. A computational study suggests a pathway involving a step-wise aziridine formation, followed by a ring-expansion to the seven-membered heterocycle. Finally, water is added in a regio-selective manner, this is accelerated by the added TsOH.

Chiral Iron Porphyrins Catalyze Enantioselective Intramolecular C(sp3 )-H Bond Amination Upon Visible-Light Irradiation

Iron-catalyzed asymmetric amination of C(sp³ )-H bonds is appealing for synthetic applications due to the biocompatibility and high earth abundance of iron, but examples of such reactions are sparse. Herein we describe chiral iron complexes of meso- and β-substituted-porphyrins that can catalyze asymmetric intramolecular C(sp³ )-H amination of aryl and arylsulfonyl azides to afford chiral indolines (29 examples) and benzofused cyclic sulfonamides (17 examples), respectively, with up to 93 % ee (yield: up to 99 %) using 410 nm light under mild conditions. Mechanistic studies, including DFT calculations, for the reactions of arylsulfonyl azides reveal that the Fe(NSO₂ Ar) intermediate generated in situ under photochemical conditions reacts with the C(sp³ )-H bond through a stepwise hydrogen atom transfer/radical rebound mechanism, with enantioselectivity arising from cooperative noncovalent interactions between the Fe(NSO₂ Ar) unit and the peripheral substituents of the chiral porphyrin scaffold.

Visible-Light-Induced Decarboxylation of Dioxazolones to Phosphinimidic Amides and Ureas

A visible-light-induced external catalyst-free decarboxylation of dioxazolones was realized for the bond formation of N=P and N-C bonds to access phosphinimidic amides and ureas. Various phosphinimidic amides and ureas (47 examples) were synthesized with high yields (up to 98%) by this practical strategy in the presence of the system's ppm Fe.