Synthesis of 2-Aryl-5-oxo-5 H -thiopyrano[4,3- b ]pyridine-7-carboxylic Acids as the First Representatives of a New Hete
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Synthesis of 2-Aryl-5-oxo-5H-thiopyrano[4,3-b]pyridine-7-carboxylic Acids as the First Representatives of a New Heterocyclic System T. I. Chabana,* and V. S. Matiychukb a Danylo
Halytsky Lviv National Medical University, Lviv, 79010 Ukraine Franko National University of Lviv, Lviv, 79005 Ukraine *e-mail: [email protected]
b Ivan
Received April 3, 2020; revised April 3, 2020; accepted April 12, 2020
Abstract—A series of ethyl 2-[(Z)-(4-oxo-2-thioxo-1,3-thiazolidin-5-ylidene)methyl]-6-arylnicotinoates was obtained as a result of the reaction of 6-aryl-2-formylnicotinoates with rhodanine. Under alkaline conditions, they underwent recyclization to form 2-aryl-5-oxo-5H-thiopyrano[4,3-b]pyridine-7-carboxylic acids—the first representatives of new heterocyclic system. Keywords: thiopyrano[4,3-b]pyridine-5-one, pyridine, thiopyran, rhodanine
DOI: 10.1134/S1070363220080290 Isocoumarins are an important class of organic compounds. They are widespread in nature and exhibit a broad spectrum of biological activity [1–3]. At the same time, isothiocoumarins have been little studied, the number of methods for their production is limited, and data on their biological activity are scarce. A convenient method for constructing an isothiocoumarin ring is the reaction of ortho-formylbenzoic acids with rhodanine (2-thioxothiazolidine-4-one) followed by recyclization of the formed 5-arylidenerodanine in a basic medium [4, 5]. This approach has also been successfully applied to the synthesis of thiopyrano[4,3-c]quinolines [6]. In continuation of our studies on the annulation reactions of the pyran [7] and thiopyran rings [8–11], herein we reported the synthesis of thiopyrano[4,3-b]pyridine-5-one derivatives 5а–5e, the first representatives of new heterocyclic system. Ethyl 6-aryl-2-formylnicotinoates 1a–1e [12] were used as the starting materials for the preparation of the target compounds. Ethyl 2-[(Z)(4-oxo-2-thioxo-1,3-thiazolidin-5-ylidene)methyl]-6arylnicotinoates 3a–3e were obtained in high yields by reacting compounds 1а–1e with rhodanine 2 in boiling acetic acid in the presence of triethylamine (Scheme 1). Under the action of an aqueous alkali solution, the rhodanine ring opens with the formation of mercapto acids
4а–4e. The latter upon acidification undergo cyclization to form the target 2-aryl-5-oxo-5H-thiopyrano[4,3-b]pyridine-7-carboxylic acids 5а–5e. The resulting compounds are high-melting substances, soluble in DMF, DMSO, and acetic acid when heated, and insoluble in non-polar solvents and water. Structure of the obtained derivatives 3a–3e and 5a–5e was proved using 1H NMR spectroscopy method. In conclusion, a simple method was developed for the synthesis of 2-aryl-5-oxo-5H-thiopyrano[4,3-b]pyridine7-carboxylic acids as the first representatives of a new heterocyclic system. General procedure for the synthesis of ethyl 6-aryl2-[(Z)-(4-oxo-2-thioxo-1,3-thiazolidin-5-ylidene)methyl]nicotinoates 3а–3e. A mixture of 2.0 mmol of ethyl 6-aryl-2-formylnicotinoate 1a–1e and 2.0 mmol of rhodanine 2 was dissolv
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