Abstract:With the aim of exploring the best reaction conditions for the diastereoselective synthesis of the 1,4-thiazepan-3-ones (4) and 4-thiazolidinones (5), we have studied the effect on solvent variation and the aggregation of AlCl3 and different zeolites as Lewis acid catalysts to the three-component microwave assisted reaction between 2,3:4,5-di-O-isopropylidene--Darabino-hexos-2-ulo-2,6-pyranose (1), benzotiazole (3) and thioglycolic acid (2). Based on the results of previous studies of our group, we discuss here two microwave assisted methods: multicomponent reaction in the presence of the catalysts (Method A) and sequential reaction with generation of the corresponding intermediates and subsequent addition of the catalysts coordinated to thioglycolic acid (Method B).
We present here a new proposal for the "one pot" generation of new 4-thiazolidinones (9a-e) through a multicomponent reaction under microwave irradiation conditions, using aromatic and heteroaromatic amines (8a-e), absolute ethanol as a "green" solvent and modifying the aldehyde group in the glycosidic residue, synthesized from D-mannitol. The study is focused in the variation of the irradiation times and the concentration of thioglycolic acid in order to study the possibility of controlling the structure and/or stereochemistry of the products formed in the reaction. Thiazolidinones 9a-d were obtained with a 69-82% The generation of the corresponding reaction products were monitored by TLC and CG-MS, taking reaction aliquots. The conditions reaction proved to be chemoselective depending on the excess of acid and irradiation times.
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