Ring-chain isomerism in conjugated guanylhydrazones: Experimental and theoretical study
| Autor: | Sanjay K. Mandal, Prasad V. Bharatam, Sumit S. Chourasiya, Deepika Kathuria, Uwe Beifuss, Asit K. Chakraborti |
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| Rok vydání: | 2018 |
| Předmět: |
Quantum chemical
010405 organic chemistry Chemistry Organic Chemistry Nuclear magnetic resonance spectroscopy Conjugated system 010402 general chemistry Ring (chemistry) 01 natural sciences Biochemistry Medicinal chemistry 0104 chemical sciences Chain (algebraic topology) Drug Discovery Proton NMR Single crystal |
| Zdroj: | Tetrahedron. 74:2857-2864 |
| ISSN: | 0040-4020 |
| Popis: | Treatment of 1,3-diaryl-propene-2-one with aminoguanidine under acidic conditions for a short reaction period (1 h) delivers - in accordance with a literature report - the corresponding guanylhydrazones. However, when the reaction time was increased to 12 h, formation of the ring annulated product 4,5-dihydro-1H-pyrazole-1-carboximidamide was observed. This is the first case of ring-chain isomerism in conjugated guanylhydrazones. The acyclic conjugated guanylhydrazone and the corresponding annulated product (4,5-dihydro-1H-pyrazole-1-carboximidamide) could be clearly distinguished by means of UV and NMR spectroscopy. The formation of the ring isomer was further confirmed by single crystal XRD analysis. The time-dependent 1H NMR study indicated the gradual transformation of the open-chain compound into the cyclic one. The mechanistic insights into the formation of these two products were explored using quantum chemical methods which revealed that the ring isomer is thermodynamically more stable than the open-chain isomer by 6–11 kcal/mol and the barrier for cyclization was found to be 31.37 kcal/mol. |
| Databáze: | OpenAIRE |
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