Intermolecular Acetoxyaminoalkylation of α-Diazo Amides with (Diacetoxyiodo)benzene and Amines

Exploring Diazo Compounds for the Divergent Electro-Cascade Sequence and S-H Insertion Reaction

We have explored the reactivity of diazo compounds under electrochemical conditions to establish a cascade sequence of thiolation/cyclization/reduction reactions. Electrolyzing styryl diazo imides and aryl thiols enables direct access to a single diastereoisomer of 2,5-pyrrolidine-dione-fused thiochromans in good yield under mild and metal-free conditions. Notably, a tunable reactivity has been achieved via S-H insertion at the diazo center in modified reaction conditions. Based on the experimental evidences, including the detection of key intermediates and computational studies, the mechanism for the electrochemical cascade reaction has also been established.

Electrochemical oxidative difunctionalization of diazo compounds with two different nucleophiles

With the fast development of synthetic chemistry, the introduction of functional group into organic molecules has attracted increasing attention. In these reactions, the difunctionalization of unsaturated bonds, traditionally with one nucleophile and one electrophile, is a powerful strategy for the chemical synthesis. In this work, we develop a different path of electrochemical oxidative difunctionalization of diazo compounds with two different nucleophiles. Under metal-free and external oxidant-free conditions, a series of structurally diverse heteroatom-containing compounds hardly synthesized by traditional methods (such as high-value alkoxy-substituted phenylthioacetates, α-thio, α-amino acid derivatives as well as α-amino, β-amino acid derivatives) are obtained in synthetically useful yields. In addition, the procedure exhibits mild reaction conditions, excellent functional-group tolerance and good efficiency on large-scale synthesis. Importantly, the protocol is also amenable to the key intermediate of bioactive molecules in a simple and practical process.

Enroute sustainability: metal free C-H bond functionalisation

The term "C-H functionalisation" incorporates C-H activation followed by its transformation. In a single line, this can be defined as the conversion of carbon-hydrogen bonds into carbon-carbon or carbon-heteroatom bonds. The catalytic functionalisation of C-H bonds using transition metals has emerged as an atom-economical technique to engender new bonds without activated precursors which can be considered as a major drawback while attempting large-scale synthesis. Replacing the transition-metal-catalysed approach with a metal-free strategy significantly offers an alternative route that is not only inexpensive but also environmentally benign to functionalize C-H bonds. Recently metal free synthetic approaches have been flourishing to functionalize C-H bonds, motivated by the search for greener, cost-effective, and non-toxic catalysts. In this review, we will highlight the comprehensive and up-to-date discussion on recent examples of ground-breaking research on green and sustainable metal-free C-H bond functionalisation.

[2 + 3] Annulative Coupling of Tetrahydroisoquinolines with Aryliodonio diazo compounds To Access 1,2,4-Triazolo[3,4-a]isoquinolines

Base promoted one-pot annulative coupling of 1,2,3,4-tetrahydroisoquinolines (THIQs) with hypervalent iodine(III) species aryliodonio diazo compounds has been devised for the direct construction of 1,2,4-triazolo[3,4-a]isoquinoline derivatives at room temperature in open air for the first time. This approach involves [2 + 3] cascade annulation of nucleophilic THIQ with an electrophilic aryliodonio diazo compound via N-H and α-C1(sp³)-H difunctionalization of THIQ.

Electrochemistry and Reactivity of Chelation-stabilized Hypervalent Bromine(III) Compounds

Hypervalent bromine(III) reagents possess a higher electrophilicity and a stronger oxidizing power compared to their iodine(III) counterparts. Despite the superior reactivity, bromine(III) reagents have a reputation of hard-to-control and difficult-to-synthesize compounds. This is partly due to their low stability, and partly because their synthesis typically relies on the use of the toxic and highly reactive BrF3 as a precursor. Recently, we proposed chelation-stabilized hypervalent bromine(III) compounds as a possible solution to both problems. First, they can be conveniently prepared by electro-oxidation of the corresponding bromoarenes. Second, the chelation endows bromine(III) species with increased stability while retaining sufficient reactivity, comparable to that of iodine(III) counterparts. Finally, their intrinsic reactivity can be unlocked in the presence of acids. Herein, an in-depth mechanistic study of both the electrochemical generation and the reactivity of the bromine(III) compounds is disclosed, with implications for known applications and future developments in the field.

Base Mediated Diazirination via Iodine(III) Reagents

Herein, we described an efficient method for the construction of highly functionalized diazirines from the carbohydrazide and diazo-substituted hypervalent iodine reagents. Unambiguous transformation has been designed with user applicable and easy practicable conditions. Remarkably, d-glucose, menthol, aspirin, proline, and lithocholic acid were efficiently diazirinated. Furthermore, the method is mild, robust, and highly selective, which successfully converted a variety of aryl, alkyl, benzyl, and heterocyclic hydrazides into the corresponding diazirine derivatives.

Multicomponent Reactions Involving Diazo Reagents: A 5-Year Update

This review summarizes recent developments in multicomponent reactions of diazo compounds. The role of diazo reagent and the type of interaction between components was analyzed to structure the discussion. In contrast to previous reviews on related topics mostly focused on metal catalyzed transformations, a substantial amount of organocatalytic or catalyst-free methodologies is covered in this work.

Visible-Light-Induced C(sp2)-C(sp3) Cross-Dehydrogenative-Coupling Reaction of N-Heterocycles with N-Alkyl-N-methylanilines under Mild Conditions

Disclosed herein is a cross-dehydrogenative-coupling reaction of N-heterocycles including 1,2,4-triazine-3,5(2H, 4H)-diones and quinoxaline-2(1H)-ones with N-methylanilines to form C(sp²)-C(sp³) under visible-light illumination and ambient air at room temperature. In this process, easily available Ru(bpy)₃Cl₂·6H₂O serves as the catalyst, and air acts as the green oxidant. This method features high atom economy, environmental friendliness, and convenient operation and provides an efficient and practical access to aminomethyl-substituted N-heterocycles with extensive functional group compatibility in 40-86% yields.

Iodine(III) promotes cross-dehydrogenative coupling of N-hydroxyphthalimide and unactivated C(sp3)-H bonds

Cross-dehydrogenative coupling reactions provide a method to construct new chemical bonds by direct C-H activation without any pre-functionalization. Compared to functionalization of a C-H bond α- to ether oxygen, α- to carbonyl, or at a benzylic position, functionalization of unactivated hydrocarbons is difficult and often requires high temperatures, a transition-metal catalyst, or a superstoichiometric quantity of volatile, toxic, and explosive tert-butylhydroperoxide. Here, a cross-dehydrogenative C-O coupling reaction of N-hydroxyphthalimide with unactivated alkanes, nitriles, ethers, and thioethers has been realized by using iodobenzene diacetate as the radical initiator. The current protocol enables efficient functionalization of unactivated hydrocarbons and nitriles through inert C(sp³)-H bond activation under mild reaction conditions. O-substituted NHPI derivatives are generated in good yields under metal-free conditions.

Three-Component Reaction for the Synthesis of Highly Functionalized Propargyl Ethers

Multicomponent reactions provide efficient means to access molecular complexity. Herein, we report a copper-catalyzed three-component reaction of diazo compounds, alcohols and ethynyl benziodoxole (EBX) reagents for the synthesis of propargyl ethers. Extensive variations of the three partners of the reaction is possible, leading to highly functionalized and structurally diverse products under mild conditions. Alkynylation of a copper ylide intermediate is postulated as key step for this transformation.

Reactions between Diazo Compounds and Hypervalent Iodine(III) Reagents

Site-selective "cut and sew" transformations employing diazo compounds and hypervalent iodine(III) compounds involve the departure of leaving groups, a "cut" process, followed by a reorganization of the fragments by bond formation, a "sew" process. Bearing controllable cleavage sites, diazo compounds and hypervalent iodine(III) compounds play a critical role as versatile reagents in a wide range of organic transformations because their excellent nucleofugality allows for a large number of unusual reactions to occur. In recent years, the combination of diazo compounds and hypervalent iodine(III) reagents has emerged as a promising tool for developing new and valuable approaches, and has met considerable success. In this Minireview, this combination is systematically illustrated with recent advances in the field, with the aim of elaborating the synthetic utility and potential of this concept as a powerful strategy in organic synthesis.

Diiodomethane-Mediated Generation of N-Aryliminium Ions and Subsequent [4 + 2] Cycloadditions with Olefins

Herein, we report a method for in situ generation of N-aryliminium ions via reactions of N,N-dimethylanilines with diiodomethane. We used the method to prepare tetrahydroquinolines via one-pot three-component reactions between N,N-dimethylanilines, diiodomethane, and olefins. This transformation involves initial reaction of the aniline with diiodomethane to form an iodomethylammonium salt, which undergoes fragmentation accompanied by elimination of methyl iodide to give an N-aryliminium ion, which is trapped by the olefin via [4 + 2] cycloaddition to give the final product. This method for generating N-aryliminium ions requires neither a catalyst nor a strong oxidant, suggesting that it can be expected to find broad utility, especially for substrates that are sensitive to Lewis acids, transition metals, or strong oxidants.

Synthesis of Isoxazolines and Oxazines by Electrochemical Intermolecular [2 + 1 + n] Annulation: Diazo Compounds Act as Radical Acceptors

Reported herein is an unprecedented synthesis of isoxazolines and oxazines through electrochemical intermolecular annulation of alkenes with tert-butyl nitrite, in which diazo compounds serve as radical acceptors. Notably, [2 + 1 + 2] and [2 + 1 + 3] annulations occur when styrenes and allylbenzenes are used as substrates, respectively. The latter reaction undergoes group migration to form more stable radical, manifesting radical route instead of conventional 1,3-dipolar cycloaddition occurs. Moreover, scale-up experiments suggest the potential application value of these transformations in industry.