Visible-light-mediated one-pot efficient synthesis of 1-aryl-1 H ,3 H -thiazolo[3,4- a ]benzimidazoles: a metal-free pho
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SHORT COMMUNICATION
Visible‑light‑mediated one‑pot efficient synthesis of 1‑aryl‑1H,3H‑thiazolo[3,4‑a]benzimidazoles: a metal‑free photochemical approach in aqueous ethanol Mohd Nazeef1 · Km Neha Shivhare1 · Shabir Ali2 · Saif Ansari1 · I. R. Siddiqui1 Received: 21 June 2020 / Accepted: 16 September 2020 © Springer Nature Switzerland AG 2020
Abstract A new metal-free approach to construct medicinally valuable 1-aryl-1H,3H-thiazolo[3,4-a]benzimidazoles under visible light irradiation in aqueous ethanol medium at room temperature has been developed. The present process was performed with 1,2-phenylenediamines, aromatic aldehydes and 2-mercaptoacetic acid utilizing a simple household 22 W compact fluorescent lamp to generate C–S, C–N bonds through radical intermediates. This visible-light-promoted synthesis provides lower cost, operation simplicity and high functional groups tolerating ability with short reaction time and high yield under mild reaction conditions. Graphic abstract
Keywords 1-Aryl-1H,3H-thiazolo[3,4-a]benzimidazoles · Green synthesis · Visible light · Metal-free · Ethanol–water
Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11030-020-10145-8) contains supplementary material, which is available to authorized users. * I. R. Siddiqui [email protected] 1
Laboratory of Green Synthesis, Department of Chemistry, University of Allahabad, Allahabad 211002, India
Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India
2
Heterocyclic compounds containing C–S, C–N bonds are highly attractive scaffolds due to their diverse pharmaceutical and biological applications [1, 2]. Benzimidazoles are the important structural motifs, mainly found in biologically significant drugs, functional materials and especially in natural products [3–5]. This scaffold received considerable attention in recent years because of its wide range of biological activities such as anti-cancer [6], anti-biotic [7],
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anti-microbial [8] and anti-parkinson [9]. Notably, 1H,3Hthiazolo[3,4-a]benzimidazole molecules exhibited numerous activities including anti-HIV-1 RT inhibitor [10] and anti-enterovirus activity [11] (Fig. 1). Particularly, 2,6-Difluorophenyl derivatives of benzimidazoles also displayed high potent inhibitor for HIV-1 RT and benzimidazoles containing non-nucleoside show reverse transcriptase inhibitors revealing high specificity for HIV-1 RT [12]. To minimize environmental impact, scientists are growing attention toward construction of organic compounds using a clean and environmentally friendly approach. In this perspective, green chemistry offers an alternative pathway for eco-efficient and sustainable development of chemical products which incorporate renewable materials and safer reaction media instead of hazardous substances thereby minimizing cost, waste material and product degradation [13, 14]. In recent years, visible light is prominently utilized in many chemical reactions to achieve facile and
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