Cyclization of 4‐Phenylthiosemicarbazide with Phenacylbromide Revisited. Formation of 1,3,4‐Thiadiazines and of Isomeric 1,3‐Thiazoles |
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| Authors: | Wolf‐Diethard Pfeiffer Dieter Junghans Ashot S Saghyan Peter Langer |
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| Institution: | 1. Institut für Biochemie, Universit?t Greifswald, Greifswald, Germany;2. Scientific and Production Center “Armbiotechnology” of NAS RA, Yerevan, Armenia;3. Department of Pharmaceutical Chemistry, Yerevan State University, Yerevan, Armenia;4. , Greifswald, Germany;5. Institut für Chemie, Universit?t Rostock, Rostock, Germany;6. Leibniz‐Institut für Katalyse e. V. an der Universit?t Rostock, Rostock, Germany |
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| Abstract: | The cyclization of 4‐phenylthiosemicarbazide with phenacylbromide, carried out in refluxing ethanol, afforded 1,3,4‐thiadiazine 1 as the major product. In contrast to a previous report, 2‐phenylimino‐4‐phenyl‐2,3‐dihydro‐1,3‐thiazol‐3‐amine ( 2 ) and not 2‐hydrazono‐3,4‐diphenyl‐2,3‐dihydro‐1,3‐thiazole ( 8 ) was formed as a side‐product. This product is the main product when the reaction is carried out in concentrated hydrochloric acid. Our findings were independently confirmed by independent syntheses of the isomeric products and by a thorough study of their reactivity. It is important to note that the product distribution of the cyclization of thiosemicarbazides with haloketones strongly depends on the substitution pattern and on the reaction conditions. |
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