Synthesis of Unsaturated Thioethers of N(3)-Allyl-2-Thioxoquinazolin-4-One

The quinazolinone scaffold represents a promising structural platform for the development of novel functionalized nitrogen-containing heterocyclic compounds due to its synthetic accessibility, structural stability, and broad range of biological activities. The aim of this study was to obtain previously unreported unsaturated thio derivatives of 3-allyl-2-thioxoquinazolin-4-one. For this purpose, alkylation reactions of 3-allyl-2-thioxo-2,3-dihydroquinazolin-4(3H)-one were investigated using pentenyl chloride, 3-methylbut-1-enyl chloride, and butynyl bromide in dimethylformamide. The effect of temperature on the course of the reactions was established: increasing the temperature to 40 °C afforded the corresponding terminally unsubstituted unsaturated thioethers without impurities of the starting reagents, whereas reactions performed at room temperature were accompanied by incomplete conversion. The structures of the synthesized compounds were confirmed by spectroscopic methods. The spectral data indicated alkylation of the thioxo group at the sulfur atom and confirmed the presence of the corresponding alkenyl and alkynyl fragments in the target products. The obtained results expand the range of functionalized quinazolinone derivatives and provide a basis for further investigation of their reactivity, particularly in electrophilic intramolecular heterocyclization reactions.