Ring-chain isomerism in conjugated guanylhydrazones: Experimental and theoretical study

Kathuria, Deepika ; Chourasiya, Sumit S. ; Mandal, Sanjay K. ; Chakraborti, Asit K. ; Beifuss, Uwe ; Bharatam, Prasad V. (2018) Ring-chain isomerism in conjugated guanylhydrazones: Experimental and theoretical study Tetrahedron, 74 (23). pp. 2857-2864. ISSN 0040-4020

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Official URL: http://doi.org/10.1016/j.tet.2018.04.042

Related URL: http://dx.doi.org/10.1016/j.tet.2018.04.042

Abstract

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.

Item Type:Article
Source:Copyright of this article belongs to Elsevier B.V.
Keywords:Ring-Chain; Isomerism; DFT; Guanylhydrazone; NMR.
ID Code:116311
Deposited On:12 Apr 2021 09:22
Last Modified:12 Apr 2021 09:22

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