Synthesis of benzothiazoles using fluorescein as an efficient photocatalyst under visible light

Recent Advances in the Development of Greener Methodologies for the Synthesis of Benzothiazoles

The benzothiazole ring system has been recognised with crucial pharmacophoric features being present among various approved drugs and clinical and pre-clinical candidates. The medicinal importance of this privileged scaffold stimulated the interest of synthetic medicinal/ organic chemists for the synthesis of its derivatives due to their diverse biological applications. In most of the reports in the literature, benzothiazoles were synthesized by cyclocondensation of 2- aminothiophenol with either carboxylic acid and its derivatives or aldehydes. However, many of these procedures involve reaction conditions that are not in conformity with sustainable chemistry development. The negative impact of chemicals and their manufacturing processes on the environment, human health, and biodiversity raises safety concerns. On the other hand, the utilization of non-renewable energy sources, use of rare earth metals as catalysts, involvement of costly chemicals, prolonged reaction time at high temperatures, and considerable waste generation diminish the greener impact of these reaction methodologies and make them non-sustainable. In order to avoid such drawbacks of the non-sustainable practices in the synthesis of benzothiazoles, there have been continuous efforts to develop greener methodologies for the construction of this bioactive scaffold. This review aims to delve into the literature reports on the recent advancements in the development of greener methodologies for the synthesis of bioactive benzothiazoles.

Dual Molecular Oxygen Activation Sites on Conjugated Microporous Polymers for Enhanced Photocatalytic Formation of Benzothiazoles

Oxidative formation of high value compounds involving active oxygen species using heterogeneous polymeric photocatalysts has become a useful tool in catalysis. Controlling the interaction between the active sites on polymer photocatalysts and oxygen molecules is still challenging due to the rather large polymer backbone structure. Here, we design a triazine-containing donor acceptor-type conjugated microporous polymer (CMP) containing dual major active sites at F and N atoms for molecular oxygen activation. Introducing fluorine atoms on the CMP backbone led to a combined effect of enhanced adsorption and electron transfer of oxygen. Time-resolved photoluminescence, electronic paramagnetic resonance spectra, and DFT calculation revealed favorable absorption energy and electron transfer kinetics between the CMP and oxygen molecules, thus efficiently generating superoxide radicals (O₂^•-) and singlet oxygen (¹O₂) as main active oxygen species. The photocatalytic activity, selectivity, and reusability of the CMP was demonstrated by the photocatalytic formation of a variety of benzothiazoles.

Synthesis and Biological Importance of 2-(thio)ureabenzothiazoles

The (thio)urea and benzothiazole (BT) derivatives have been shown to have a broad spectrum of biological activities. These groups, when bonded, result in the 2-(thio)ureabenzothizoles (TBT and UBT), which could favor the physicochemical and biological properties. UBTs and TBTs are compounds of great importance in medicinal chemistry. For instance, Frentizole is a UBT derivative used for the treatment of rheumatoid arthritis and systemic lupus erythematosus. The UBTs Bentaluron and Bethabenthiazuron are commercial fungicides used as wood preservatives and herbicides in winter corn crops. On these bases, we prepared this bibliography review, which covers chemical aspects of UBTs and TBTs as potential therapeutic agents as well as their studies on the mechanisms of a variety of pharmacological activities. This work covers synthetic methodologies from 1935 to nowadays, highlighting the most recent approaches to afford UBTs and TBTs with a variety of substituents as illustrated in 42 schemes and 13 figures and concluded with 187 references. In addition, this interesting review is designed on chemical reactions of 2-aminobenzothiazoles (2ABTs) with (thio)phosgenes, iso(thio)cyanates, 1,1′-(thio)carbonyldiimidazoles [(T)CDI]s, (thio)carbamoyl chlorides, and carbon disulfide. This topic will provide information of utility for medicinal chemists dedicated to the design and synthesis of this class of compounds to be tested with respect to their biological activities and be proposed as new pharmacophores.

Straightforward synthesis of quinazolin-4(3H)-ones via visible light-induced condensation cyclization

A green, simple and efficient method is developed for the synthesis of quinazolin-4(3H)-ones via visible light-induced condensation cyclization of 2-aminobenzamides and aldehydes under visible light irradiation. The reaction proceeds using fluorescein as a photocatalyst in the presence of TBHP without the need for a metal catalyst. In addition, this reaction tolerates a broad scope of substrates and could afford a variety of desirable products in good to excellent yields. Thus, the present synthetic method provides a straightforward strategy for the synthesis of quinazolin-4(3H)-ones.