Synthesis and mechanism of formation of hybrid structures comprising 2-oxochromene, thiazole and hydrazilidenechromene fragments

Abstract

Molecules with a hybrid structure containing 1,3-, 1,5-dicarbonyl fragments, based on 2H-chromen-2-one, hold significant potential as biologically active substances. A direct method has been developed for the preparation of thiosemicarbazones 2-(7-(aryl)-10,10-dimethyl-6-oxo-7,9,10,11-tetrahydro-6H,8H-chromeno[4,3-b]chromen-8-ylidene)hydrazine-1-carbothioamides. Their further modification by reaction with 3-bromoacetyl-2H-chromen-2-one was carried out, involving the thioamide group to form hybrid structures comprising 2-oxochromene, thiazole and hydrazineylidenechromene fragments (yield 71–97%). It is shown that hydrazine-1-carbothioamides can be obtained from both the initial 1,5-dicarbonyl compound and the product of its intramolecular O-heterocyclization. A one-step method is preferable, because the one-step method is preferred over the more labour-intensive two-step approach (with a similar yield). A plausible reaction mechanism is presented, based on quantum chemical calculations of few possible tautomeric forms of the intermediates and the corresponding products. A comparative analysis of the ¹H NMR spectrum of the experimental sample and the spectra of several possible final products calculated by a quantum chemical method has also confirmed the chosen reaction pathway.