Structural Determination of Spiropyrazolines and Spiropyrrolizidines by Spectral Methods
Andrey S. Kochukov1, Anna A. Meshcheryakova1, Nikolay I. Davydov1, Alisa A. Zhidkova1, Dmitry P. Vozyagin1, Nikita V. Oprishchenko1, Efrosinya M. Erkina1, Svetlana V. Borisova2, Vitaly V. Sorokin1; 1Saratov State University, Saratov, Russia; 2Saratov Higher Military Engineering School of Radiation, Chemical and Biological Defense, Saratov, Russia.
Abstract
This work describes the structural elucidation of novel spiropyrazolines and spiropyrrolizidines bearing carbonitrile, aryl, and other substituents using various one- and two-dimensional NMR spectroscopy techniques (¹H, ¹³C, COSY, NOESY, HSQC, HMBC). All compounds are generated from arylidenecarbonitriles and azomethine ylides, which are either prepared separately or formed as intermediates in multicomponent processes. The 1,3-dipolar cycloaddition reactions of azomethine ylides, leading to polysubstituted spiropyrrolizidines, exhibit specific regioselectivity and stereoselectivity depending on the nature of the starting dipolarophile and the reaction conditions. Spiropyrazolines were obtained via a one-pot, three-component condensation of cycloalkanones, malononitrile, and hydrazines. The target compounds were synthesized using a green chemistry approach—under ultrasound activation in water or a water–isopropyl alcohol mixture. The use of homo- and heteronuclear NMR correlations enabled the unambiguous identification of the spiro junction positions and other key atoms, allowing for the complete assignment of all signals and the establishment of the spatial architecture of the obtained heterocycles. Conclusions regarding the reaction pathways and product stereochemistry were drawn from the analysis of the spectral data. Some of the synthesized compounds exhibited good in vitro antibacterial activity.
Speaker
Andrey S. Kochukov
Saratov State University
Russia
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