A series of new 2-hydroxy-3-methoxybenzylidenethiazolo[3,2-a]pyrimidines with different aryl substituents at the 5 position are synthesized and characterized by ¹H/ ¹³C NMR and IR-spectroscopy and mass-spectrometry, as well as single crystal X-ray diffraction (SCXRD). It was demonstrated that the type of hydrogen bonding can play a key role in the chiral discrimination of these compounds in the crystalline phase. The hydrogen bond of the O–H...N type leads to 1D supramolecular heterochiral chains or conglomerate crystallization in the case of the formation of homochiral chains. The hydrogen bond of O–H...O type gave racemic dimers, which are packed into 2D supramolecular layers with a parallel or angular dimers arrangement. Halogen bonding of the N...Br or O...Br type brings a new motif into supramolecular self-assembly in the crystalline phase: the formation of 1D supramolecular homochiral chains instead 2D supramolecular layers. The study of cytotoxicity against various tumor cells in vitro was carried out. It was found that 2-hydroxy−3-methoxybenzylidenethiazolo[3,2-a]pyrimidines with 3-nitrophenyl substituent at C5 carbon atom demonstrated a high efficiency against M-HeLa (cervical adenocarcinoma) and low cytotoxicity against normal liver cells.

Triazolo[4,3-a]pyrimidine is one of the promising structural fragments for the development of drugs, including anticancer drugs. This work is devoted to the synthesis of a number of new 2-arylhydrazone derivatives of thiazolo[3,2-a]pyrimidine, which are synthetic precursors for triazolo[4,3-a]pyrimidines. The crystal structure of 6-acetyl-7-methyl-5-phenyl-2-(2-phenylhydrazineylidene)-5H-thiazolo[3,2-a]pyrimidin-3(2H)-one was established by SCXRD. In the reduction reaction of the compound, the following system was used: vanadium(V) oxide, and sodium borohydride in ethanol at room temperature, which led to the formation of only one pair of diastereomers (1R*)-1-((5S*,6R*,7R*)-(1-(hydroxymethyl)-7-methyl-1,5-diphenyl-1,5,6,7-tetrahydro[1,2,4]triazolo[4,3-a]pyrimidin-6-yl)ethan-1-ol.

Crystal packing of thiazolo[3,2- a ]pyrimidines was adjustable by modifying halogen position and nature in the aryl moieties, leading to diverse supramolecular structures (dimers and chains) in the solid state via various non-covalent bonds.

The [3+2]-cycloaddition of azomethinylides formed in situ to dipolarophiles is a promising approach for the synthesis of dispyroderivatives of oxindole and acenaphthenedione. In the course of our studies, it was shown that the cycloaddition of azomethinylides occurs specifically through the exocyclic double C=C bond resulting in the formation of a new pyrrolidine cycle as part of the molecule and, consequently, a dispyroheterocycle. This work is devoted to the synthesis and structural analysis of dispyrothiazolo[3,2-a]pyrimidine in the crystalline phase.

This work reports a catalyst-free, NBS-mediated rearrangement of thiazolo[3,2- a ]pyrimidines into imidazo[2,1- b ]thiazoles under mild conditions in an acetone–water system. The transformation proceeds with high diastereoselectivity and good yields.