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Abstract
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Dihyropyrano[c]chromene and tetrahydrobenzo[b]pyran derivatives are found in many naturally occurring compounds. These compounds have been used as cognitive enhancers to treat neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Down's syndrome [1]. Using different catalysts, chemists have improved the synthesis of tetrahydrobenzo[b]pyran and dihydropyrano[c]chromene derivatives through the three-component reaction of an aldehyde, malononitrile and a β-dicarbonyl compound [2]. Despite the remarkable efficiency of these catalytic systems, they have several disadvantages, such as the need for a cumbersome method of catalyst separation, release of hazardous substances into the environment, and long reaction times. In the past decade, Deep Eutectic Solvents (DESs) have been investigated as reaction media and catalysts for organic syntheses [3]. In our current work, we report the use of choline chloride (ChCl) / ascorbic acid (AA, or vitamin C) as a Natural Deep Eutectic Solvents (NADES) for the multicomponent-synthesis of pyrans and chromenes (Scheme).
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