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The click cycloaddition of azides to alkynes affording 1,2,3‐triazoles is a widely used and effective chemical transformation, applied to obtain relevant products in medicine, biology, and materials science. In this work, a set of natural deep eutectic solvents (NADESs) has been investigated in the copper‐catalyzed azide‐alkyne cycloaddition reactions (CuAAc) as green and catalytic reaction media. The use of these innovative solvents has been shown to improve the reaction effectiveness, giving excellent yields. NADESs proved to be "active" in their reducing capabilities in several cases and for the absence of added bases in all the performed reactions: DFT calculations demonstrated in fact the involvement of H‐bonds between DESs and alkynes, as well as stabilization of copper catalytic intermediates. The green experimental conditions, the absence of a base, the low temperatures, the lowering of reagent amounts, and the possibility of recycling of the solvents, outline the great potential of NADESs for CuAAc. [ABSTRACT FROM AUTHOR]

A novel rearrangement pathway of 3-alkoxycarbonyl-4-carbamoylisoxazolidines, leading to 1H-pyrrole-2,5-diones by treatment with TBAF, is reported. DFT quantum chemical calculations support the reaction route, controlled by ring strain, which proceeds through the opening of a bicyclic intermediate, with aldehyde extrusion. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of carbocyclic 2′-oxa-3′-aza-nucleosides has been described, based on the 1,3-dipolar cycloaddition of a new phosphonated nitrone with vinyl acetate followed by coupling with silylated nucleobases. The obtained compounds have been evaluated for their ability to inhibit the reverse transcriptase of avian myeloblastosis retrovirus: no significant activity has been observed. [Copyright &y& Elsevier]

Cover Feature: Base-Free Copper-Catalyzed Azide-Alkyne Click Cycloadditions (CuAAc) in Natural Deep Eutectic Solvents as Green and Catalytic Reaction Media (Eur. J. Org. Keywords: Catalytic green solvents; Click chemistry; Copper-catalyzed azide-alkyne cycloadditions; Density functional calculations; Natural deep eutectic solvents EN Catalytic green solvents Click chemistry Copper-catalyzed azide-alkyne cycloadditions Density functional calculations Natural deep eutectic solvents 4768 4768 1 09/21/21 20210914 NES 210914 B The Cover Feature b shows the use of natural deep eutectic solvents (DESs) as catalytic green solvents for the "click" Copper-catalyzed cycloaddition of azides to alkynes (CuAAc) affording 1,2,3-triazoles in excellent yields. Catalytic green solvents, Click chemistry, Copper-catalyzed azide-alkyne cycloadditions, Density functional calculations, Natural deep eutectic solvents. [Extracted from the article]

Due to their outstanding physicochemical properties, the next generation of the graphene family—graphene quantum dots (GQDs)—are at the cutting edge of nanotechnology development. GQDs generally possess many hydrophilic functionalities which allow their dispersibility in water but, on the other hand, could interfere with reactions that are mainly performed in organic solvents, as for cycloaddition reactions. We investigated the 1,3-dipolar cycloaddition (1,3-DCA) reactions of the C-ethoxycarbonyl N-methyl nitrone 1a and the newly synthesized C-diethoxyphosphorylpropilidene N-benzyl nitrone 1b with the surface of GQDs, affording the isoxazolidine cycloadducts isox-GQDs 2a and isox-GQDs 2b. Reactions were performed in mild and eco-friendly conditions, through the use of a natural deep eutectic solvent (NADES), free of chloride or any metal ions in its composition, and formed by the zwitterionic trimethylglycine as the -bond acceptor, and glycolic acid as the hydrogen-bond donor. The results reported in this study have for the first time proved the possibility of performing cycloaddition reactions directly to the p-cloud of the GQDs surface. The use of DES for the cycloaddition reactions on GQDs, other than to improve the solubility of reactants, has been shown to bring additional advantages because of the great affinity of these green solvents with aromatic systems. [ABSTRACT FROM AUTHOR]

A new template of C-4'-truncated phosphonated nucleosides (TPCOANs) has been obtained in good yields according to two different routes which exploit the reactivity of a phosphonated nitrone. The one-step procedure based on the 1,3-dipolar cycloaddition of a phosphonated nitrone with vinyl nucleobases leads to the unnatural a-nucleosides as the main adducts. On the other hand, the target β-anomers have been obtained in high yield by a two-step procedure based on the I ,3-dipolar cycloaddition of a phosphonated nitrone with vinyl acetate followed by nucleosidation reaction. The reactivity of the phosphonated nitrone has been investigated trough quantum mechanical DET calculations at the B3LYP/D95+(d,p) theory leveL Preliminary biological assays show that β-anomers of TPCOANs are able to inhibit the reverse trancriptase of different retroviruses at concentrations in the nanomolar range, with a potency comparable with that of tenofovir. [ABSTRACT FROM AUTHOR]

A new class of homo-N,O-nucleosides has been designed, based on the 1,3-dipolar cycloaddition of C-substituted nitrones with allyl nucleobases. The N-methyl-C-ethoxycarbonyl nitrone , and the C-α-silyloxymethyl-N-methyl nitrone have been exploited: the stereochemical features of the obtained nucleosides are dependent on the nature of the dipole. The results obtained with DFT calculations fully agree with the experimental results and successfully reproduce the experimentally observed reversal of endo/exo selectivity for nitrones and . [Copyright &y& Elsevier]

The diastereo- and enantioselective synthesis of α- and β-3′-hydroxymethyl-N,O-nucleosides is described, based on the 1,3-dipolar cycloaddition of a N-glycosyl nitrone. Two approaches have been evaluated: the one-step procedure, which uses vinyl nucleobases, showed a better stereoselectivity towards β-nucleosides. [Copyright &y& Elsevier]

Abstract: An efficient synthetic route to isoxazolidinyl analogues of tiazofurin has been developed. The strategy involves, as a key step, a 1,3-dipolar cycloaddition between acrylonitrile and chiral nonracemic nitrones. An opposite diastereofacial induction was observed when the chiral group was placed at either the carbon atom or the nitrogen one of the nitrone function. The 2-cyano isoxazolidines obtained were further converted into the enantiomeric target compounds by constructing the thiazole ring via condensation with l-cysteine. [Copyright &y& Elsevier]

The cycloaddition reaction between C-(2-thiazolyl) nitrones and allylic alcohol takes place with complete exo selectivity when the reactions are carried out in the presence of 1 equiv of zinc triflate. The rate of the reaction is increased enormously under microwave irradiation. The use of a chiral dipolarophile allowed application of the methodology to the synthesis of a hitherto unknown enantiomerically pure isoxazolidinyl analogue of the C-nucleoside tiazofurin. [ABSTRACT FROM AUTHOR]

The 1,3-dipolar cycloaddition reactions of five d-glyceraldehyde nitrones with alkyl acrylates and Oppolzer''s sultam acrylamide have been studied in detail, the study including double chiral induction experiments. A complete theoretical study of the reaction has also been carried out using density functional methods (B3LYP/6-31G*) in which both ortho and meta channels leading to 3,5- and 3,4-disubstituted isoxazolidines, respectively, were considered. The adducts obtained from the cycloaddition reactions have been further used for the stereoselective synthesis of protected 4-hydroxy pyroglutamic acids, particularly the (2S,4S)-isomer, which is prepared from the major adducts of the cycloaddition reactions. [Copyright &y& Elsevier]