Convenient Synthesis of 2-Amino-4H-chromenes from Photochemically Generatedo-Quinone Methides and Malononitrile

Alkoxyalkylation of Electron-Rich Aromatic Compounds

Alkoxyalkylation and hydroxyalkylation methods utilizing oxo-compound derivatives such as aldehydes, acetals or acetylenes and various alcohols or water are widely used tools in preparative organic chemistry to synthesize bioactive compounds, biosensors, supramolecular compounds and petrochemicals. The syntheses of such molecules of broad relevance are facilitated by acid, base or heterogenous catalysis. However, degradation of the N-analogous Mannich bases are reported to yield alkoxyalkyl derivatives via the retro-Mannich reaction. The mutual derivative of all mentioned species are quinone methides, which are reported to form under both alkoxy- and aminoalkylative conditions and via the degradation of the Mannich-products. The aim of this review is to summarize the alkoxyalkylation (most commonly alkoxymethylation) of electron-rich arenes sorted by the methods of alkoxyalkylation (direct or via retro-Mannich reaction) and the substrate arenes, such as phenolic and derived carbocycles, heterocycles and the widely examined indole derivatives.

A Novel Anion Exchange Membrane for Bisulfite Anion Separation by Grafting a Quaternized Moiety through BPPO via Thermal-Induced Phase Separation

Ion-exchange membranes are the core elements for an electrodialysis (ED) separation process. Phase inversion is an effective method, particularly for commercial membrane production. It introduces two different mechanisms, i.e., thermal induced phase separation (TIPS) and diffusion induced phase separation (DIPS). In this study, anion exchange membranes (AEMs) were prepared by grafting a quaternized moiety (QM,2-[dimethylaminomethyl]naphthalen-1-ol) through brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) via the TIPS method. Those membranes were applied for selective bisulfite (HSO₃^-) anion separation using ED. The membrane surface morphology was characterized by SEM, and the compositions were magnified using a high-resolution transmission electron microscope (HRTEM). Notably, the membranes showed excellent substance stability in an alkali medium and in grafting tests performed in a QM-soluble solvent. The ED experiment indicated that the as-prepared membrane exhibited better HSO₃^- separation performance than the state-of-the-art commercial Neosepta AMX (ASTOM, Japan) membrane.

Organophotoredox-Catalyzed Intermolecular Oxa-[4+2] Cycloaddition Reactions

An intermolecular oxa-[4+2] cycloaddition reaction promoted by a thioxanthylium photoredox catalyst under irradiation with green light has been developed. The reaction of ortho-quinone methides with styrenes smoothly affords the desired cycloadducts. Especially styrenes bearing electron-donating groups are efficiently transformed in this reaction. This method represents a sustainable way to carry out oxa-[4+2] cycloaddition reactions using only a catalytic amount of a photocatalyst and visible light.

Synthesis of Benzothiophene-Fused Pyran Derivatives via Piperidine Promoted Domino Reaction

A new domino reaction between thioaurones and malononitrile has been reported. This reaction allows efficient access to benzothiophene-fused pyran derivatives in good yields under mild reaction conditions. The substrate scope is broad; a series of benzothiophene-fused pyran derivatives have been synthesized.

A simple green protocol for the synthesis of ethyl 3-amino-1-aryl-1H-benzo[f] chromene-2-carboxylates in aqueous media

An eco-friendly and efficient straightforward method has been developed for the synthesis of ethyl 3-amino-1-aryl-1 H-benzo[ f]chromene-2-carboxylate derivatives via 1,4-diazabicyclo[2.2.2]octane (DABCO)-catalysed cyclisation of β-naphthol and 3-aryl-2-cyanoacrylates using water as a green solvent. All products precipitated from the reaction mixture and were isolated by simple filtration. No further work-up nor purification was necessary. The structure of ethyl 3-amino-1-aryl-1 H-benzo[ f]chromene-2-carboxylate was further confirmed by X-ray single crystal analysis.

Development of a Brønsted acid Al–MIL-53 metal–organic framework catalyst and its application in [4 + 2] cycloadditions

Two Brønsted acid Al–MIL-53 derived metal–organic frameworks were developed to serve as efficient [4 + 2] cycloaddition catalysts.