POLITAG-M-F as Heterogeneous Organocatalyst for the Waste-Minimized Synthesis of β-Azido Carbonyl Compounds in Batch and under Flow Conditions

We herein report a waste minimization protocol for the β-azidation of α,β-unsaturated carbonyl compounds using TMSN3. The selection of the appropriate catalyst (POLITAG-M-F), in combination with the reaction medium, resulted in enhanced catalytic efficiency and a low environmental footprint. The thermal and mechanical stability of the polymeric support allowed us to recover the POLITAG-M-F catalyst for up to 10 consecutive runs. The CH3CN:H2O azeotrope has a 2-fold positive effect on the process, increasing the efficiency of the protocol and minimizing waste generation. Indeed, the azeotropic mixture, used as a reaction medium and for the workup procedure, was recovered by distillation, leading to an easy and environmentally friendly procedure for product isolation in high yield and with a low E-factor. A comprehensive evaluation of the environmental profile was performed by the calculation of different green metrics (AE, RME, MRP, 1/SF) and a comparison with other literature available protocols. A flow protocol was defined to scale-up the process, and up to 65 mmol of substrates were efficiently converted with a productivity of 0.3 mmol/min.

Chemical versatility of azide radical: journey from a transient species to synthetic accessibility in organic transformations

The generation of azide radical (N₃˙) occurs from its precursors primarily via a single electron transfer (SET) process or homolytic cleavage by chemical methods or advanced photoredox/electrochemical methods. This in situ generated transient open-shell species has unique characteristic features that set its reactivity. In the past, the azide radical was widely used for various studies in radiation chemistry as a 1e^- oxidant of biologically important molecules, but now it is being exploited for synthetic applications based on its addition and intermolecular hydrogen atom transfer (HAT) abilities. Due to the significant role of nitrogen-containing molecules in synthesis, drug discovery, biological, and material sciences, the direct addition onto unsaturated bonds for the simultaneous construction of C-N bond with other (C-X) bonds are indeed worth highlighting. Moreover, the ability to generate O- or C-centered radicals by N₃˙ via electron transfer (ET) and intermolecular HAT processes is also well documented. The purpose of controlling the reactivity of this short-lived intermediate in organic transformations drives us to survey: (i) the history of azide radical and its structural properties (thermodynamic, spectroscopic, etc.), (ii) chemical reactivities and kinetics, (iii) methods to produce N₃˙ from various precursors, (iv) several significant azide radical-mediated transformations in the field of functionalization with unsaturated bonds, C-H functionalization via HAT, tandem, and multicomponent reaction with a critical analysis of underlying mechanistic approaches and outcomes, (v) concept of taming the reactivity of azide radicals for potential opportunities, in this review.

Asymmetric α-Chlorination of β-Keto Esters Using Hypervalent Iodine-Based Cl-Transfer Reagents in Combination with Cinchona Alkaloid Catalysts

We herein report an unprecedented strategy for the asymmetric α-chlorination of β-keto esters with hypervalent iodine-based Cl-transfer reagents using simple Cinchona alkaloid catalysts. Our investigations support an α-chlorination mechanism where the Cinchona species serves as a nucleophilic catalyst by reacting with the chlorinating agent to generate a chiral electrophilic Cl-transfer reagent in situ. Using at least 20 mol-% of the alkaloid catalyst allows for good yields and enantioselectivities for a variety of different β-keto esters under operationally simple conditions.

Iron-Catalyzed Alkylazidation of 1,1-Disubstituted Alkenes with Diacylperoxides and TMSN3

An iron-catalyzed radical alkylazidation of electron-deficient alkenes is reported. Alkyl diacyl peroxides work as the alkyl source, and trimethylsilyl azide acts as the azido reservoir. This method features mild reaction conditions, wide substrate scope, and good functional group tolerance, providing a range of α-azido esters, an α-azido ketone, and an α-azido cyanide in high yields. These azides can be easily transferred into many kinds of amino acid derivatives.

Electrophilic chloro(ω-alkoxy)lation of alkenes employing 1-chloro-1,2-benziodoxol-3-one: facile synthesis of β-chloroethers

A four-component reaction for electrophilic chloro(ω-alkoxy)lation of alkenes has been described. The stable chloro-iodine(iii) reagent and SOCl2 were used as electrophilic and nucleophilic chlorine sources, respectively. This approach provides a straightforward way to synthesize various useful β-chloro ω-chloroalkyl ethers from a wide range of alkenes, including electron-deficient, aromatic and unactivated alkenes. The synthetic applications of this approach were also explored in some useful transformations.

Solvent-tuned chemoselective carboazidation and diazidation of alkenes via iron catalysis

A solvent-tuned chemoselective carboazidation and diazidation of alkenes with CH₂Cl₂ and TMSN₃ through iron catalysis has been described.

Recent Applications of the Zhdankin Reagent in Organic Synthesis

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Intermolecular, redox-neutral azidoarylation of alkenes via photoredox catalysis

An intermolecular, redox-neutral azidoarylation of alkenes with pyridines and TMSN₃ has been reported via visible light-induced photoredox catalysis.

Catalytic Regio- and Enantioselective Haloazidation of Allylic Alcohols

Herein we report a highly regio- and stereoselective haloazidation of allylic alcohols. This enantioselective reaction uses readily available materials and can be performed on a variety of alkyl-substituted alkenes and can incorporate either bromine or chlorine as the electrophilic halogen component. Both halide and azido groups of the resulting products can be transformed into valuable building blocks with complete stereospecificity. The first example of an enantioselective 1,4-haloazidation of a conjugated diene is reported as well as its application to a concise synthesis of an aza-sugar.

Asymmetric Catalytic Halofunctionalization of α,β-Unsaturated Carbonyl Compounds

Halofunctionalization methods enable the vicinal difunctionalization of alkenes with heteroatom nucleophiles and halogen moieties. As a fundamental transformation in organic synthesis, the catalytic asymmetric variants have only recently been reported. In sharp contrast to the asymmetric halocyclization of simple alkenes which involves a nucleophile-assisted alkene activation process, the asymmetric halofunctionalization of enones developed by our laboratory features an electrophile-assisted 1,4-addition pathway. Our work in this area has resulted in the development of several different types of regio-, diastereo-, and enantioselective processes, including inter- and intramolecular haloaminations, haloetherifications, and haloazidations. The scope, updated mechanism, limitations, and future perspective of these reactions are discussed.

Catalytic enantioselective synthesis of α-chiral azides

The catalytic asymmetric synthesis of α-chiral azides is of current interest and three synthetic strategies have been developed. This review summarizes the recent progress in this research area, discusses the advantages and limitations of each strategy, and outlines synthetic opportunities for future research.

Fe-Catalyzed three-component carboazidation of alkenes with alkanes and trimethylsilyl azide

Iron out the difference. Carboazidation of alkenes using cycloalkanes, CH₂Cl₂, CHCl₃ and CCl₄ as alkylating reagents proceeded smoothly in the presence of TMSN₃, DTBP and a catalytic amount of Fe(acac)₃ to afford chain extended alkyl azides and γ-azido chloroalkanes in good to high yields.

Iron-Catalyzed Asymmetric Haloazidation of α,β-Unsaturated Ketones: Construction of Organic Azides with Two Vicinal Stereocenters

Organic azides play important roles in synthetic chemistry, chemical biology, drug discovery, and material science. Azido-functionalization of alkenes is one of the most efficient procedures for rapid introduction of azide group into organic compounds. But only a few examples have been documented in the catalytic asymmetric version of the azidation of alkenes. Herein, we report an unprecedented highly diastereo- and enantioselective bromoazidation of α,β-unsaturated ketones catalyzed by chiral N,N'-dioxide/Fe(OTf)₂ complexes. An array of aryl, heteroaryl, and alkyl substituted α,β-unsaturated ketones were transformed to the corresponding α-bromo-β-azido ketones in high yields with excellent diastereo- and enantioselectivities. The catalytic system was also applicable for chloroazidation and iodoazidation of chalcone. Kinetic studies and some control experiments suggested that the reaction might proceed via a 1,4-addition/halogenation pathway.

Electronic halocyclization and radical haloazidation of benzene-linked 1,7-dienes for the synthesis of functionalized 3,1-benzoxazines

Electronic halocyclization and radical haloazidation of benzene-linked 1,7-dienes by using TMSN₃ as an azidyl source and NBS as a halogen source has been disclosed in this paper, producing a series of functionalized 3,1-benzoxazines in moderate to good yields.