Two series of functionalized imidazothiazolotriazine derivatives were synthesized via the condensation of imidazo[4,5-e]-1,2,4-triazine-3-thiones with acetylenedicarboxylic acid dimethyl and diethyl esters (DMAD and DEAD) and subsequent base-catalyzed rearrangement of the obtained imidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazines into regioisomeric imidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazine derivatives.

Novel reactivity of pyridinium ylides in reaction with annulated 4-oxothiazolidin-5-ylidenes as electron-deficient alkenes involving a cascade Michael addition/elimination process is described. The method provides a broad variety of functionalized products available from dipolarophiles with different substituents within the heterocyclic system as well as pyridinium salts with different electron-withdrawing groups (EWG = CO₂R, COPh, COMe, CN) in mild conditions with good to excellent yields.

A series of imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazines was synthesized via a cascade sequence of hydrolysis and skeletal rearrangement of imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazin-7(8H)-ylidene)acetic acid esters in methanol upon treatment with excess KOH. Imidazo[4,5-e]thiazolo[3,2-b][1,2,4]triazin-6(7H)-ylidene)acetic acid esters are also suitable substrates for the reaction. In this case hydrolysis and thiazole ring expansion were accompanied with the change of the thiazolotriazine junction type from thiazolo[3,2-b][1,2,4]triazine to thiazino[2,3-c][1,2,4]triazine.

Highly diastereoselective methods for the synthesis of two series of regioisomeric polynuclear dispyroheterocyclic compounds with five or six chiral centers, comprising moieties of pyrrolidinyloxindole and imidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazine of linear structure or imidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazine of angular structure, have been developed on the basis of a [3+2] cycloaddition of azomethine ylides to functionalized imidazothiazolotriazines. Depending on the structure of the ethylenic component, cycloaddition proceeds as an anti-exo process for linear derivatives, while cycloaddition to angular ones resulted in a syn-endo diastereomer. Novel pathways of isomerization for the synthesized anti-exo products upon treatment with sodium alkoxides have been found, which resulted in two more series of diastereomeric dispiro[imidazothiazolotriazine-pyrrolidin-oxindoles] inaccessible with the direct cycloaddition reaction. For the first series, the inversion of the configuration of one stereocenter, i.e., C-4′ atom of the pyrrolidine cycle, (epimerization) was established. For the second one, configuration of the obtained diastereomer formally corresponded to the syn-endo approach of the azomethine ylide in the case of cycloaddition to the ethylenic component.