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Abstract

The hazardous and toxic nature of many solvents, in particular organic solvents that are extensively used in large scale for organic reactions have transformed a serious threat to the environment. Therefore, the design of solvent-free catalytic reaction has received considerable attention during recent times in the field of green synthesis. A solvent-free or solid state reaction may be accomplished using the reactants single or merge them in clays, zeolites, silica, alumina or other substrates. Esters, thioesters and amides are important and valuable compounds in the area of industry, medicine, pharmaceutical and heterocyclic chemistry. In this paper, various solventfree systems to synthesize esters, thioesters and amides via the acylation of alcohols, phenols, thiols and amines are described. In this review we summarized the activities presented mainly the recent years. reusable catalyst for the synthesis of esters and amides under solvent-free conditions (Scheme 5). 50 Scheme 3. Solvent-free diacylation of aldehydes using ATPB. Scheme 4. Solvent-free acylation of alcohols, thiols and amines catalyzed by ZrOCl 2 .8H 2 O.An convenient method with the same reagents and in the presence of lithium bis(perfluoroalkylsulfonyl)-imide (LiPFS-I) has also been developed (Scheme 24). 76 Scheme 24. Solvent-free acylation of alcohols using LiPFSI.Another practical and highly efficient strategy was also described with SiO 2 -Co(acac) 2 and SiO 2 -Cu(acac) 2 under solvent-free conditions (Scheme 25). 77 The acylation of alcohols, phenols and amines with acetyl chloride was carried out in less than 60 min at 50 0 C. The esterification of alcohols and amines was performed respectively with SiO 2 -Cu(acac) 2 and SiO 2 -Co(acac) 2. Scheme 25. Solvent-free acylation of alcohols and amines using SiO 2 -Co(acac) 2 and SiO 2 -Cu(acac) 2 . 7 M. Kazemi et al Journal of Medicinal and Chemical Sciences Review J. Med. Chem. Sci. 2019, 1, 1-8 http://jmchemsci.com Scheme 30. Solvent-free diacylation of aldehydes catalyzed by n-Sulfonic acid poly4-vinylpyridinum) hydrogen sulfate.