Computational studies of the cyclization of thiosemicarbazides |
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Authors: | Agata Siwek Piotr Paneth |
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Institution: | 1. Department of Organic Chemistry, Faculty of Pharmacy, Medical University, Staszica 6, 20–081 Lublin, Poland;2. Institute of Applied Radiation Chemistry, Technical University, Zeromskiego 116, 90–924 Lodz, PolandInstitute of Applied Radiation Chemistry, Technial University, Zeromskiego 116, 90‐924 Lodz, Poland.=== |
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Abstract: | While typically cyclodehydration of thiosemicarbazides in acidic media leads to 1,3,4‐thiadiazoles, we have recently shown that under reflux conditions in anhydrous acetic acid the cyclization yields an imidazolidine derivative. The mechanism of this reaction has been characterized theoretically. Calculations indicate that this direction, facilitated by the presence of the ? CH2CO2? moiety in the N4 substituent is favored over the direction leading toward the thiadiazole product. Formation of the C? N bond that closes the five‐member ring appears to be concerted with the departure of ethanol molecule, although the proton transfer from the nitrogen atom to oxygen atom is much more advanced in the transition state. Copyright © 2007 John Wiley & Sons, Ltd. |
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Keywords: | 1 3 4‐thiadiazole cyclization DFT theoretical calculations |
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