Transformations of sym-octahydroxanthene-1,8-diones and 1,8-dioxo-sym-octahydroxanthylium salts in recyclization under the influence of amines

N-, O- and S-Heterocycles Synthesis in Deep Eutectic Solvents

The synthesis of heterocycles is a fundamental area of organic chemistry that offers enormous potential for the discovery of new products with important applications in our daily life such as pharmaceuticals, agrochemicals, flavors, dyes, and, more generally, engineered materials with innovative properties. As heterocyclic compounds find application across multiple industries and are prepared in very large quantities, the development of sustainable approaches for their synthesis has become a crucial objective for contemporary green chemistry committed to reducing the environmental impact of chemical processes. In this context, the present review focuses on the recent methodologies aimed at preparing N-, O- and S-heterocyclic compounds in Deep Eutectic Solvents, a new class of ionic solvents that are non-volatile, non-toxic, easy to prepare, easy to recycle, and can be obtained from renewable sources. Emphasis has been placed on those processes that prioritize the recycling of catalyst and solvent, as they offer the dual benefit of promoting synthetic efficiency while demonstrating environmental responsibility.

Sustainable synthesis of 1,8-dioxooctahydroxanthenes in deep eutectic solvents (DESs)

The DES formed from ZrOCl₂·8H₂O and ethylene glycol was used as a catalyst as well as reaction medium for the synthesis of 9-aryl-1,8-dioxooctahydroxanthenes.

Calcined Layered Double Hydroxides: Catalysts for Xanthene, 1,4-Dihydropyridine, and Polyhydroquinoline Derivative Synthesis

This work is generally focused on the synthesis of NiFeTi-layered double hydroxides (LDHs) using a hydrothermal route, which were calcined at various temperatures (varying from 200 to 600 °C). The synthesized materials were physicochemically characterized. X-ray diffraction results revealed the loss of the layered structure on calcination resulting in the formation of layered double oxides (LDOs) or mixed metal oxides, which was also supported by Fourier transform infrared studies. Scanning electron microscopy results also show loss of the layered structure and the creation of LDOs on increasing the temperature. These LDOs were tested as the catalysts for the synthesis of biologically significant xanthene, 1,4-dihydropyridine, and polyhydroquinoline derivatives. Among all, NiFeTi LDH calcined at 600 °C proved to be the best catalyst for the synthesis of these derivative compounds under optimized conditions. The advantages obtained were excellent yields in a lesser reaction time. Stability and reusability were also assessed; the catalyst was stable even after five cycles. Furthermore, the memory effect of the obtained NiFeTi CLDH calcined at 600 °C confirms that the material so formed is a calcined state of LDH itself. High catalytic efficiency, easy fabrication, and recycling ability of NiFeTi CLDH calcined at 600 °C make it a potential catalyst for the synthesis of xanthene, 1,4-dihydropyridine, and polyhydroquinoline derivatives.

2,4,6-Trichloro-1,3,5-Triazine-Promoted Synthesis of 1,8-Dioxo-Octahydroxanthenes under Solvent-Free Conditions

A practical protocol has been developed for the synthesis of 1,8-dioxo-octahydroxanthenes from aromatic aldehydes and 5,5-dimethylcyclohexane-1,3-dione under solvent-free conditions in the presence of wet 2,4,6-trichloro-1,3,5-triazine (TCT, cyanuric chloride). The desired products were obtained in high yields with a simple and environmentally benign procedure.