Recent developments in green approaches for sustainable synthesis of indole-derived scaffolds

1,3-Dipolar cycloaddition reactions of isatin-derived azomethine ylides for the synthesis of spirooxindole and indole-derived scaffolds: recent developments

The unique therapeutic and biological characteristics of spirooxindole have led to the presentation of numerous reactions for the synthesis of spirooxindoles through 1,3-Dipolar cycloaddition of highly reactive isatin-derived azomethine ylides with activated olefins as the main tool for the formation of spirocyclic oxindoles during the last 4 years. Therefore, there is a need to highlight the recent developments in this area, along with the representative synthetic methods and relevant reaction mechanisms from 2018 to 2021. The representative synthetic methodologies were listed in four sections based on the procedure to form the azomethine ylide species including isatins and amino acids, isatin-derived α-(trifluoromethyl)imine, isatins and benzylamines, and from isatin-derived cyclic imine 1,3-dipoles.

Green Chemistry in Organic Synthesis: Recent Update on Green Catalytic Approaches in Synthesis of 1,2,4-Thiadiazoles

Green (sustainable) chemistry provides a framework for chemists, pharmacists, medicinal chemists and chemical engineers to design processes, protocols and synthetic methodologies to make their contribution to the broad spectrum of global sustainability. Green synthetic conditions, especially catalysis, are the pillar of green chemistry. Green chemistry principles help synthetic chemists overcome the problems of conventional synthesis, such as slow reaction rates, unhealthy solvents and catalysts and the long duration of reaction completion time, and envision solutions by developing environmentally benign catalysts, green solvents, use of microwave and ultrasonic radiations, solvent-free, grinding and chemo-mechanical approaches. 1,2,4-thiadiazole is a privileged structural motif that belongs to the class of nitrogen–sulfur-containing heterocycles with diverse medicinal and pharmaceutical applications. This comprehensive review systemizes types of green solvents, green catalysts, ideal green organic synthesis characteristics and the green synthetic approaches, such as microwave irradiation, ultrasound, ionic liquids, solvent-free, metal-free conditions, green solvents and heterogeneous catalysis to construct different 1,2,4-thiadiazoles scaffolds.