Direct Regioselective Alkylation of Non-Basic Heterocycles with Alcohols and Cyclic Ethers through a Dehydrogenative Cross-Coupling Reaction under Metal-Free Conditions

Organic Peroxides in Transition-Metal-Free Cyclization and Coupling Reactions (C-C) via Oxidative Transformation

Transition-metal-free transformations are recognized as green and sustainable methods for constructing carbon-carbon bonds in organic synthesis. This review describes the application of six organic peroxides, including tert-butyl hydroperoxide (TBHP), di-tert-butyl peroxide (DTBP), tert-butyl peroxybenzoate (TBPB), benzoyl peroxide (BPO), dialauroyl peroxide (DLP), and diguyl peroxide (DCP), in C-C bond construction, highlighting selected examples and mechanisms of challenging transformations. Each section concludes with a detailed overview of suitable reagents for various coupling reactions and strengths and weaknesses of the reported works. This work aims to inspire further innovations in transition-metal-free oxidative transformations, promoting sustainable and eco-friendly chemical processes and paving the way for new peroxide-based organic synthesis methods.

Bis(thienyl)ethenes with α-methoxymethyl groups. Syntheses, spectroscopic Hammett plots, and stabilities in PMMA films

A series of bis(thienyl)ethenes (BTEs) possessing perfluorocyclopentene backbones and methoxymethyl groups (MOM) in the 2/2'-positions of the thiophenes was prepared and examined. The substitution pattern of the 5/5'-positions was varied, covering the range from electron-donating to electron-withdrawing. The substituent effects of the absorption wavelengths of the ring-opened and the ring-closed isomers, which are interconverted by reversible 6π-electrocyclizations and cycloreversions, are studied by means of the spectroscopic Hammett equation and the Hammett-Brown equation. Excellent correlations of these linear free energy relationships were found, when the σp values of the Hammett equation, which summarize inductive, mesomeric and field effects, were replaced to the Hammett-Brown σp+ and σp- values which also take direct conjugation into account. We studied solvent effects on the spectroscopic properties and embedded the BTEs into polymethylmethacrylate (PMMA) coatings to examine their fatigue resistance. By our studies, the spectroscopic properties of BTEs can be adjusted by variation of the substitution pattern to a desired excitation wavelength for switching processes.

K2S2O8-Mediated Hydroxyalkylation of Benzothiazoles with Alcohols in Aqueous Solution

The K2S2O8-mediated hydroxyalkylation of 2H-benzothiazoles with aliphatic alcohols in aqueous solution was described. The mild and convenient protocol generated a series of hydroxyalkylated benzothiazoles in moderate to good yields. Besides, benzimidazole and ethers were also compatible in this reaction, leading to corresponding C2 ether-substituted heteroarenes.

A visible light mediated, metal and oxidant free highly efficient cross dehydrogenative coupling (CDC) reaction between quinoxalin-2(1H)-ones and ethers

The white light mediated, 3C alkylation of quinoxalin-2(1H)-ones via a cross dehydrogenative coupling (CDC) reaction with cyclic ethers using eosin Y as a photocatalyst is described. The reaction proceeds via a hydrogen abstraction and transfer process.

A ruthenium-catalyzed alkenylation–annulation approach for the synthesis of indazole derivatives via C–H bond activation

A new approach to indazole derivatives through a Ru(ii)-catalyzed C–H activation–annulation reaction, which proceeds via C–C and C–N bond forming reactions, is reported.

Copper-catalyzed oxidative coupling of quinoxalin-2(1H)-ones with alcohols: access to hydroxyalkylation of quinoxalin-2(1H)-ones

An efficient protocol for the synthesis of hydroxyl-containing quinoxalin-2(1H)-ones has been developed via the copper-catalyzed cross-coupling reaction of quinoxalin-2(1H)-ones with alcohols with moderate to good yields.