A new rearrangement in the thiazolopyrimidine series: from 2-arylmethylidenthiazolo[3,2-a]pyrimidines to 2,3-dihydrothiazolo[3,2-a]pyrimidine-2-carboxylates.

The chemistry of heterocyclic compounds is one of the most important areas of organic chemistry. Such structures include 5H-thiazolo[3,2-a]pyrimidine derivatives. However, few methods of modification of such derivatives are known in the literature. This is due to the fact that all chemical properties are based either on interaction with sufficiently strong nucleophilic reagents (CH-acids and cyclic disulfides) or on hydrolytic instability under acidic conditions. Furthermore, there is no information on reactivity with O-nucleophiles.

Therefore, microwave irradiation was applied as one of the effective alternative activation method. The significant reduction in reaction time and higher yields of products made this alternative heating source an attractive tool in organic synthesis. It became possible to carry out the methanolysis reaction of 2-arylmethylidentiazolo[3,2-a]pyrimidine derivatives leading to the previously unknown 2,3-disubstituted 2,3-dihydrothiazolo[3,2-a]pyrimidine derivatives in almost quantitative yields.

The investigation revealed that a single pair of stereoisomers is formed during the reaction. The formation of S-, R-, R- and R-, S-, S- isomers with trans-orientation between substituents at asymmetric carbon atoms was observed. It was thus demonstrated that the reaction proceeded diastereoselectively. Additionally, it was observed that the reaction of 2-arylmethylidentiazolo[3,2-a]pyrimidine derivatives with aqueous methanol in the presence of pyridine for 12 hours resulted in the formation of hydrolysis products, namely 3,5-diaryl-2,3-dihydro-5H-thiazolo[3,2-a]pyrimidine-2-carboxylic acids, in good yields.

Thus, this work is devoted to the selective synthesis of 2,3-disubstituted-2,3-dihydrothiazolo[3,2-a]pyrimidine derivatives and the study of their structure. The obtained derivatives were characterized by a complex of physicochemical methods.