Base-Promoted Tandem Pathway for Keto-Amides: Visible Light-Mediated Room-Temperature Amidation Using Molecular Oxygen as an Oxidant

Herein, we report metal- and photocatalyst-free room-temperature amidation for α-ketoamide synthesis from feedstock phenacyl bromides and amines using molecular oxygen as an oxidant as well as a source of oxygen in the amide segment. Visible light-mediated base-promoted one-pot sequential C-N/C═N/C═O bond formation takes place in a tandem manner to afford the desired product. Functional group tolerance (benzylic alcohol, keto, cyano, nitro, halo, etc.), a broad substrate scope, and gram-scale synthesis make this synthetic methodology more attractive. We have observed that electron-rich aromatic amines, aliphatic amines, and phenacyl bromide derivatives proceeded the present transformation with marginally superior reactivity in comparison to electron-deficient aromatic amines and phenacyl bromide derivatives. Moreover, several control experiments, in situ isolation of secondary amine and imine as key intermediates, and 18O-labeling experiments provide complete insight into the mechanism of the tandem pathway.

Progress in organocatalysis with hypervalent iodine catalysts

Hypervalent iodine compounds as environmentally friendly and relatively inexpensive reagents have properties similar to transition metals. They are employed as alternatives to transition metal catalysts in organic synthesis as mild, nontoxic, selective and recyclable catalytic reagents. Formation of C-N, C-O, C-S, C-F and C-C bonds can be seamlessly accomplished by hypervalent iodine catalysed oxidative functionalisations. The aim of this review is to highlight recent developments in the utilisation of iodine(III) and iodine(V) catalysts in the synthesis of a wide range of organic compounds including chiral catalysts for stereoselective synthesis. Polymer-, magnetic nanoparticle- and metal organic framework-supported hypervalent iodine catalysts are also described.

Heteroarylation of Ethers, Amides, and Alcohols with Light and O2

An efficient protocol for the C_α-H heteroarylation of ethers, amides, and alcohols using air and light under mild conditions is described. The reaction is applicable to a wide spectrum of functional groups. The generation of C-radicals via photoinduced aerobic oxidation of ethers, amides, and alcohols is the key feature of the process. Control experiments suggest a radical pathway for the reaction.

Aldehyde-catalyzed epoxidation of unactivated alkenes with aqueous hydrogen peroxide

The organocatalytic epoxidation of unactivated alkenes using aqueous hydrogen peroxide provides various indispensable products and intermediates in a sustainable manner. While formyl functionalities typically undergo irreversible oxidations when activating an oxidant, an atropisomeric two-axis aldehyde capable of catalytic turnover was identified for high-yielding epoxidations of cyclic and acyclic alkenes. The relative configuration of the stereogenic axes of the catalyst and the resulting proximity of the aldehyde and backbone residues resulted in high catalytic efficiencies. Mechanistic studies support a non-radical alkene oxidation by an aldehyde-derived dioxirane intermediate generated from hydrogen peroxide through the Payne and Criegee intermediates.

Photoinduced Aerobic Iodoarene-Catalyzed Spirocyclization of N-Oxy-amides to N-Fused Spirolactams*

Iodoarene catalysis is a powerful methodology that usually requires an excess of oxidant, or of redox mediator if the terminal oxidant is dioxygen, to generate the key hypervalent iodine intermediate to proceed efficiently. We report that, using the spiro-cyclization of amides as a benchmark reaction, aerobic iodoarene catalysis can be enabled by relying on a pyrylium photocatalyst under blue light irradiation. This unprecedented dual organocatalytic system allows the use of low catalytic loading of both catalysts under very mild operating conditions.

PIFA-Mediated Dearomatizative Spirocyclization of Phenolic Biarylic Ketones via Oxidation and C-C Bond Cleavage

The dearomatizing spirocyclization of phenolic biarylic ketones using PhI(OCOCF₃)₂ as oxidant is presented. The reaction affords various cyclohexadienones through C-C bond cleavage under mild conditions. Mechanistic investigations reveal that an exocyclic enol ether acts as the key intermediate in the transformation.

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

β-Hydroxyalkylphosphine sulfides undergo [1,3]- or [1,4]-sulfur atom phosphorus-to-carbon migration in the presence of Lewis or Brønsted acids. The direction of sulfur atom migration depends on the type of acid used for the reaction. In the presence of a Brønsted acid, mainly [1,3]-rearrangement is observed, whereas a Lewis acid catalyzes the [1,4]-sulfur migration. To gain insight into the mechanism of these transformations, the stereochemistry of these rearrangements have been tested, along with the conduction of some control experiments and DFT calculations.

Recent Advances in the Applications of the Intramolecular Suzuki Cross-coupling Reaction in Cyclization and Heterocyclization: An Update

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The palladium-catalyzed reaction of aryl halide and boronic acid for the formation of C–C bonds so-called Suzuki–Miyaura cross-coupling reaction has many applications in Modern Synthetic Organic Chemistry. In 2013, we emphasized the applications of the intramolecular Suzuki cross-coupling reaction in cyclization and heterocyclization. Due to a plethora relevant papers appeared in the chemical literature, herein, we wish to cover by updating our previous review, the applications of the intramolecular Suzuki cross-coupling reaction in cyclization and heterocyclization leading to various homocyclic and heterocyclic compounds reported during a period of 2013 to 2018.

Aerobically-initiated C(sp3)–H bond amination through the use of activated azodicarboxylates

In this article we report a procedure for α-C(sp³)–H amination of ethereal compounds through use of azodicarboxylates as the nitrogen source and freely-available atmospheric oxygen to access ethereal radical intermediates via aerobic C–H activation.

Harnessing Autoxidation of Aldehydes: In Situ Iodoarene Catalyzed Synthesis of Substituted 1,3,4-Oxadiazole, in the Presence of Molecular Oxygen

Isobutyraldehyde underwent auto-oxidation in the presence of molecular oxygen to generate an acyloxy radical under a "metal-free" environment. They were subsequently exploited in situ to afford hypervalent iodines with p-anisolyl iodide which generated substituted 1,3,4-oxadiazoles in moderate to excellent yields from N'-arylidene acetohydrazides. The reaction strategy tolerated diverse substitution on the hydrazide substrates. Control experiments and literature precedence supported the formation of an in situ iodosylarene complex that facilitates the formation of products.

Sodium Hypochlorite Pentahydrate as a Reagent for the Cleavage of trans-Cyclic Glycols

Sodium hypochlorite pentahydrate (NaOCl·5H₂O) can be used toward the efficient glycol cleavage of trans-cyclic glycols, which are generally resistant to this transformation. Interestingly, the reaction of cis-cyclic glycols with NaOCl·5H₂O is slower than that observed for the corresponding trans-isomer. This trans selectivity is in sharp contrast to traditional oxidants used for glycol cleavage. Acyclic glycols can also react efficiently with NaOCl·5H₂O to form their corresponding carbonyl compounds in high yield.

Recent advances in metal-free aerobic C–H activation

An overview of recent reactions based on the metal-free, dioxygen-induced, C–H activation of various radical precursors.

Oxidative Decarboxylation Enables Chemoselective, Racemization-Free Esterification: Coupling of α-Ketoacids and Alcohols Mediated by Hypervalent Iodine(III)

An α-ketoacid could be converted into a reactive acylating agent by treatment with hypervalent iodine(III) species, and in so doing, we discovered a novel decarboxylative acylation of alcohols that affords a variety of esters in excellent yields. The esterification has been applied to a sterol bearing a free carboxylic acid and shows unique chemoselectivity. The procedure is racemization-free and operates under mild conditions.

Electrochemical Hofmann rearrangement mediated by NaBr: practical access to bioactive carbamates

An electrochemical Hofmann rearrangement is reported. With the mediation of NaBr, highly corrosive and toxic halogens are avoided. Moreover, this efficient and green approach is well compatible with a broad range of amides, including several commercial medicine derivatives, and provides direct access to synthetically useful carbamates. The synthetic utility of this method is also demonstrated by the preparation of ¹⁵N labeling carbamate and gram-scale synthesis of Amantadine.

Oxidation Catalysis by an Aerobically Generated Dess-Martin Periodinane Analogue

Hypervalent iodine(V) reagents, such as Dess-Martin periodinane (DMP) and 2-iodoxybenzoic acid (IBX), are broadly useful oxidants in chemical synthesis. Development of strategies to generate these reagents from dioxygen (O₂ ) would immediately enable use of O₂ as a terminal oxidant in a broad array of substrate oxidation reactions. Recently we disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidation. In this work, aerobic oxidation of iodobenzenes is coupled with disproportionation of the initially generated I(III) compounds to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidation chemistry analogous to that of DMP. The developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidation catalysis.

Oxidase catalysis via aerobically generated hypervalent iodine intermediates

The development of sustainable oxidation chemistry demands strategies to harness O₂ as a terminal oxidant. Oxidase catalysis, in which O₂ serves as a chemical oxidant without necessitating incorporation of oxygen into reaction products, would allow diverse substrate functionalization chemistry to be coupled to O₂ reduction. Direct O₂ utilization suffers from intrinsic challenges imposed by the triplet ground state of O₂ and the disparate electron inventories of four-electron O₂ reduction and two-electron substrate oxidation. Here, we generate hypervalent iodine reagents-a broadly useful class of selective two-electron oxidants-from O₂. This is achieved by intercepting reactive intermediates of aldehyde autoxidation to aerobically generate hypervalent iodine reagents for a broad array of substrate oxidation reactions. The use of aryl iodides as mediators of aerobic oxidation underpins an oxidase catalysis platform that couples substrate oxidation directly to O₂ reduction. We anticipate that aerobically generated hypervalent iodine reagents will expand the scope of aerobic oxidation chemistry in chemical synthesis.