Spectroscopic investigation, component analysis and DFT calculations of tautomeric forms of substituted dihydro-6H-chromeno[4,3-d]pyrazolo[1,5-a]pyrimidin-6-one

Introduction

The scientific community faces the challenge of creating complex organic compounds from simple substratesusing environmental criteria, safety and efficiency ofthe synthetic procedures. Well-known method in this regard, particularly in the synthesis of azaheterocycles is Biginelli multicomponent reaction, which allows to vary the nature of the reagents involved in the reaction, and the conditions of its implementation.

The combined experimental and theoretical study of the spectral characteristics of molecular systems is one of the most important modern tools for solving problems of current organic chemistry. Such an approach is relevant for a correct description of the composition and structure of the reaction mixtures of biologically active compounds, especially when it comes to mobile tautomeric equilibrium.

Experimental details

Chromenopirazolopyrimidinone (CPP) was synthesized using microwave radiation in the absence of solvent by a multicomponent reaction of 4-hydroxy-2H-chromen-2-one with 5-amine-1H-pyrazole and benzaldehyde. CPP was characterized by a set of spectroscopic methods (FTIR, UV-Vis, NMR, LDI-MS). Decomposition of UV-Vis spectra was performed by component analysis implemented in MILCA algorithm.

Results and Discussion

CPP exists as a mixture of tautomeric forms, the structure of which was examined by means of an integrated approach using spectroscopic methods and quantum chemistry. As was shown by MILCA algorithm, UV-Vis spectra obtained in different solvents of various polarity contain bands of all tautomeric forms. Decomposition of the absorption spectra of CPP in various solvents on the individual components of the absorption showed the presence of two tautomers. The molar ratios of tautomeric forms depend on polarity of solvent used.