A ball-milling strategy for the synthesis of benzothiazole, benzimidazole and benzoxazole derivatives under solvent-free conditions

Abstract

A convenient solvent-free method for the synthesis of benzothiazole, benzimidazole, and benzoxazole derivatives has been developed using recyclable ZnO-NPs via a ball-milling strategy. The method affords environmentally friendly reaction conditions that score high on the ecoscale with the low E-factor. The process is also highly efficient even on a multi-gram scale and provides easy product isolation. Fig. 1 Biologically active benzothiazole derivatives. † Electronic supplementary information (ESI) available. See

Tailoring of Hetero–oligophenylene Stabilized Nanohybrid Materials: Potential Tandem Photo‐Promoted Systems for C–C and C–X Bond Formation Reactions via C‐H Activation

“…Furthermore, the target molecules were purified by recrystallization from organic solvent [THF and EtOH (1:1)] and no coloumn chromatography was needed for purification of final products. To understand the role of aggregates of derivative 3 in the photo‐promoted efficiency of ZnO NPs, bare ZnO NPs were prepared by following the reported method [(sol‐gel) method] . Bare ZnO NPs were then utilized for carrying out the model reaction.…”

“…To understand the role of aggregates of derivative 3 in the photo-promoted efficiency of ZnO NPs, bare ZnO NPs were prepared by following the reported method [(sol-gel) method]. [18] Bare ZnO NPs were then utilized for carrying out the model reaction. The model reaction afforded the desired product in relatively lower yield (79 %) in 1.5 h (entry 2, Table 2).…”

Metal-catalyzed organic reactions using mechanochemistry

“…69 Exploration of the catalyst loading, milling frequency and time revealed the best catalytic activity is Scheme 7. Mechanochemical zinc-catalyzed allylic alkylation.…”

“…68 achieved, for the most active ZnO-NPs, after 30 min of milling at 600 rpm by using just 0.5 mol% of the catalyst (Scheme 8). 69 All reaction readily generated the respective heterocycles in high yields and, importantly, the mechanosynthesis was readily scalable to several grams. The products were readily separated from catalyst by simple washing with water and methanol, allowing the catalyst to be re-used.…”

“…Mechanochemical synthesis of benzothiazoles, benzoxazoles and benzimidazoles catalyzed by ZnO nanoparticles 69. …”