Synlett

Chemical upcycling of polystyrene (PS) is one of the most promising approaches to plastic waste reuse and to achieve economic development goals. However, it remains a huge challenge because PS has only chemically inert covalent bonds. As part of an ongoing study, we herein describe the development, scope, and mechanism of photoinduced iron catalysis for the selective oxidative degradation of polystyrene to benzoic acid. A series of commonly found polystyrene products could be degraded to benzoic acid efficiently. A plausible mechanism involving radical-based stepwise aerobic oxidation was proposed.

1,2,3-Triazoles are a privileged class of heterocycles in medicinal and agrochemical science. Here, we describe the base-promoted [3+2] annulation of carbodiimides with diazoacetonitrile. This reaction protocol permits access to a variety of novel 5-amino-4-cyano-1,2,3-triazoles in a regiospecific manner. Further derivatization is exemplified by a skeletal rearrangement and an N-functionalization of triazole products.

The versatility of aza- and oxa-heterocyclic compounds has garnered significant attention in recent times. A large number of currently approved pharmaceutical products include nitrogen- and oxygen-containing heterocycles. Recent nanotechnological developments have propelled an upsurge in the applications of nanocatalysis for heterocyclic synthesis. Metal nanoparticles (MNPs) have emerged as promising catalysts for the synthesis of aza- and oxa-heterocycles owing to their unique physicochemical properties. Various MNPs including gold, silver, nickel and palladium have been evaluated for their catalytic activities in different reaction types, including cyclisation, coupling, hydrogenation and oxidative transformations. The MNPs have exhibited remarkable catalytic efficiency when utilised under optimal conditions. These catalysts have showcased high reusability and recyclability, yielding satisfactory amounts of the desired heterocyclic compound. The present work provides a detailed overview of recent advances in the area of MNP-assisted synthetic construction of aza- and oxa-heterocycles, published during the previous calendar year, 2022. The review serves as a valuable resource and also paves the way for future investigations in the development of novel catalytic strategies for heterocycle synthesis.1 Introduction2 Nanocatalysis3 Aza- and Oxa-Heterocycle Synthesis Catalysed by MNPs3.1 AuNPs3.2 CuNPs3.3 CoNPs3.4 FeNPs3.5 NiNPs3.6 PdNPs3.7 PtNPs3.8 SiNPs3.9 ZnNPs3.10 Bimetallic NPs3.11 Other MNPs4 Summary and Outlook

The introduction of allyl fluorides as alternative electrophiles in asymmetric allylic alkylation reactions has recently attracted significant interest. Despite the intrinsic thermodynamically demanding C–F bond-cleavage event, the fluorophilic nature of the silicon atom is key in assisting the activation and cleavage of the allylic C–F bond. Thus, the use of silylated compounds as unconventional nucleophiles, together with the Lewis basicity of fluorine when acting as a leaving group, enables the development of innovative chemical transformations within mild and selective catalytic schemes. This Synpacts article summarizes the diverse defluorinative asymmetric allylic alkylations with allyl fluorides reported to date under both chiral Lewis base and transition-metal catalysis.

A blue LED-induced three-component coupling of a carbamoyl radical, cyclic enone, and allylstannane was developed. The use of blue LEDs and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) as a radical initiator permitted the three-component radical coupling to proceed with a high chemoselectivity. An elucidation of the mechanism revealed a pathway for the formation of a tributyltin radical from TPO and allylstannane. This tandem radical reaction is expected to be applicable in natural-product synthesis.

2′-Deoxy-2′-β-fluoro-4′-azido-5-fluorouridine, a new pyrimidine nucleoside analogue of azvudine (FNC), was designed and synthesized. The synthesis of this nucleoside analogue was achieved by bromination of 1,3,5-O-tribenzoyl-2-deoxy-2-fluoro-d-arabinofuranoside, followed by reaction with silylated 5-fluorouracil and further modifications of the sugar moiety, in a 7.6% overall yield over nine steps. The product exhibited good antiviral activity against HIV-1 infection in HEK293T cells.

We describe a photocatalytic reaction of diazo compounds with allyl sulfides under visible-light reaction conditions. In the presence of Ru(bpy)3Cl2 as a photocatalyst, a [2,3]-sigmatropic rearrangement reaction occurs that leads to the formation of homoallylic sulfides. This reaction proceeds in acetone as the solvent, which is unusual in carbene-transfer reactions, and it shows a broad substrate scope in the rearrangement reaction of allylic sulfides.

An efficient strategy for rapid assembly of the complex substituted cyclohexene core that is present in several cyclic imine marine toxins is presented. Several of these toxins, including pinnatoxin A and recently discovered portimine A, have been the focus of much attention due to their fascinating biological activities. We demonstrate that the substituted cyclohexene-diene motif, which is a challenging feature to access synthetically, can be prepared through a stepwise Ireland–Claisen rearrangement/enyne metathesis procedure beginning from chiral esters. This approach enables a divergent strategy that can be implemented in syntheses of cyclic imines or derivatives thereof.

Heterocycles have gained recognition as vital components in approved drugs, drawing substantial attention from the scientific community. Ionic liquids (ILs) have been utilized for their transformative roles in heterocycle synthesis, showcasing distinctive properties that are pivotal in diverse chemical transformations, while also acting as effective catalysts and offering safer alternatives to volatile organic solvents. This account delves into the synthesis of nitrogen- and oxygen-containing heterocyclic structures, employing various ILs such as ammonium, cholinium, DABCO-based, DBU-based, guanidinium-based, imidazolium, phosphonium, pyridinium, and other miscellaneous examples. They have proven indispensable in facilitating reactions like the Fischer indole synthesis, the Biginelli reaction, Knoevenagel condensations and many more. Notably, the recyclability of ILs serves as a valuable asset, aiding in the completion of intricate synthetic pathways, multicomponent reactions, and one-pot syntheses, ultimately enhancing yields. This account, covering the literature published in 2022, seeks to guide researchers in selecting suitable ILs for specific chemical reactions that enable the synthesis of aza- and/or oxa-heterocycles. The described advancements represent promising prospects for drug development and other applications within the domain of heterocyclic chemistry.1 Introduction2 Construction of Heterocycles Catalyzed by Ionic Liquids2.1 Ammonium Ionic Liquids2.2 Cholinium-Based Ionic Liquids2.3 DABCO-Based Ionic Liquids2.4 DBU-Based Ionic Liquids2.5 Guanidinium-Based Ionic Liquids2.6 Imidazolium Ionic Liquids
2.7 Phosphonium Ionic Liquids2.8 Pyridinium Ionic Liquids2.9 Other Ionic Liquids3 Summary and Outlook4 Abbreviations

Since their discovery in the 1950s, C-nucleosides have piqued the interest of both biologists and medicinal chemists. In this regard, C-nucleosides and their synthetic analogues have resulted in promising leads in drug design. Concurrently, advances in chemical syntheses have contributed to structural diversity and drug discovery efforts. Convergent and modular approaches to synthesis have gained much attention in this regard. Among them nucleophilic substitution at C-1 has seen wide applications, providing flexibility in synthesis, good yields, the ability to maneuver stereochemistry as well as to incorporate structural modifications. In this account, we briefly discuss the modular synthesis of C-nucleosides with a focus on mechanistic studies and sugar modifications that have resulted in potent lead molecules. Meanwhile, various FDA-approved C-nucleoside analogues have been reported previously for their antiviral and/or anticancer potential, with examples being pyrazomycin, remdesivir, pseudouridine, and pseudouridimycin.1 Introduction and Motivation2 Strategies for the Synthesis of C-Nucleosides3 Biologically Active C-Nucleosides4 Mechanistic Analysis of C-Nucleoside Formation5 Synthesis and Manipulation of Medicinally Important C-Nucleoside Analogues6 C-Nucleosides: Synthesis of C–C Bonds with a C-1′ Base7 Conclusion