Synthesis of Xanthones, Thioxanthones and Acridones by a Metal-Free Photocatalytic Oxidation Using Visible Light and Molecular Oxygen

K2CO3-Catalyzed Dual C-C-Coupled Cyclization to 3-Amino-4-benzoylbiphenyls and In Situ I2-Catalyzed C-N Bond Forming Annulation: A Metal-Free Synthesis of Arylacridones

Unprecedented metal-free cyclization catalysis reactions are developed in a highly regioselective fashion to synthesize 3-amino-4-benzoyl biphenyls and arylacridones with high atom economy. Catalytic K2CO3 is utilized as the only reagent for the unusual rapid dual C-C-coupled cyclization between β-keto enamines and cinnamaldehydes to furnish the functionalized biphenyls. Its C(sp2)-H functionalized C-N bond-forming cyclization was performed in situ using molecular I2 as a catalyst to furnish valuable arylacridones. Plausible mechanisms for the new cyclization reactions are predicted by conducting various control experiments and ESI-MS analyses.

Ionic Organic Solid 1,3-Bis(sulfomethyl)imidazoliumate as an Effective Metal-Free Catalyst for Sustainable Organic Syntheses

The 1,3-bis(sulfomethyl)imidazole (bsmim) was effectively prepared by a multicomponent reaction, employing aminomethanesulfonic acid, glyoxal, and formaldehyde. The catalytic activity of bsmim was tested in the synthesis of quinoline derivatives, by means of the Friedländer reaction, and in the allylic substitution of alcohols with nitrogen-containing heterocycles. The performance of sulfo-imidazole derivative (bsmim) resulted in higher comparison with the carboxyimidazole analogs (bcmim and bcmimCl), under the same reaction conditions. This type of ionic organic solid allows the promotion of reactions in the absence of solvent and mild reaction conditions, which improves the sustainability of organic synthetic processes.

A Double-Edged Sword: Thioxanthenes Act on Both the Mind and the Microbiome

The rising tide of antibacterial drug resistance has given rise to the virtual elimination of numerous erstwhile antibiotics, intensifying the urgent demand for novel agents. A number of drugs have been found to possess potent antimicrobial action during the past several years and have the potential to supplement or even replace the antibiotics. Many of these ‘non-antibiotics’, as they are referred to, belong to the widely used class of neuroleptics, the phenothiazines. Another chemically and pharmacologically related class is the thioxanthenes, differing in that the aromatic N of the central phenothiazine ring has been replaced by a C atom. Such “carbon-analogues” were primarily synthesized with the hope that these would be devoid of some of the toxic effects of phenothiazines. Intensive studies on syntheses, as well as chemical and pharmacological properties of thioxanthenes, were initiated in the late 1950s. Although a rather close parallelism with respect to structure activity relationships could be observed between phenothiazines and thioxanthenes; several thioxanthenes were synthesized in pharmaceutical industries and applied for human use as neuroleptics. Antibacterial activities of thioxanthenes came to be recognized in the early 1980s in Europe. During the following years, many of these drugs were found not only to be antibacterial agents but also to possess anti-mycobacterial, antiviral (including anti-HIV and anti-SARS-CoV-2) and anti-parasitic properties. Thus, this group of drugs, which has an inhibitory effect on the growth of a wide variety of microorganisms, needs to be explored for syntheses of novel antimicrobial agents. The purpose of this review is to summarize the neuroleptic and antimicrobial properties of this exciting group of bioactive molecules with a goal of identifying potential structures worthy of future exploration.