Diastereodivergent synthesis of dispiroheterocyclic structures comprising pyrrolidinyloxindole and imidazothiazolotriazine moieties

Diastereoselective Synthesis of Dispiro[Imidazothiazolotriazine-Pyrrolidin-Oxindoles] and Their Isomerization Pathways in Basic Medium

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.

Synthesis, Structure and Stereochemistry of Dispirocompounds Based on Imidazothiazolotriazine and Pyrrolidineoxindole

Methods for the synthesis of two types of isomeric dispirocompounds based on imidazothiazolotriazine and pyrrolidineoxindole, differing in the structure of imidazothiazolotriazine fragment, namely, linear dispiro[imidazo[4,5-e]thiazolo[3,2-b][1,2,4]triazine-6,3'-pyrrolidine- 4',3″-indolines] and angular dispiro[imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazine-7,3'-pyrrolidine-4',3″-indolines] were proposed. The first method relies on a 1,3-dipolar cycloaddition of azomethine ylides generated in situ from paraformaldehyde and N-alkylglycine derivatives to the corresponding oxindolylidene derivatives of imidazothiazolotriazine. The cycloaddition leads to a mixture of two diastereomers resulted from anti- and syn-approaches of azomethine ylide in approximately a 1:1 ratio, which were separated by column chromatography. Another method consists in rearrangement of linear dispiro[imidazo[4,5-e]thiazolo[3,2-b][1,2,4]triazine-6,3'-pyrrolidine-4',3″-indolines] into hitherto unavailable angular dispiro[imidazo[4,5-e]thiazolo[2,3-c]-[1,2,4]triazine-7,3'-pyrrolidine-4',3″-indolines] upon treatment with KOH. It was found that the anti-diastereomer of linear type underwent rearrangement into the isomeric angular syn-diastereomer, while the rearrangement of the linear syn-diastereomer gave the angular anti-diastereomer.

Tandem Michael addition/elimination – novel reactivity of pyridinium ylides in reaction with electron-deficient alkenes

Novel reactivity of pyridinium ylides in reaction with 4-oxothiazolidin-5-ylidenes as electron-deficient alkenes involving a tandem Michael addition/elimination process was developed to give double bond functionalization products in mild conditions.

Activator free diastereoselective 1,3-dipolar cycloaddition: a quick access to coumarin based spiro multi heterocyclic adducts

A formal diastereoselective 1,3-dipolar cycloaddition of azomethine ylide and coumarin derivatives to construct coumarin based spiro multi heterocyclics has been described. The in situ generation of azo-ylide was achieved for various heterocyclic carbonyls (indenoquinoxaline and isatin). This transformation is also suitable for maleimide dipolarophiles for the synthesis of hydro-maleimide derivatives. These decarboxylative annulations neither required any catalyst nor any activator. Further the pure products were isolated by filtration from the reaction mixture after the reaction under ambient conditions.

A formal diastereoselective decarboxylative 1,3-dipolar cycloaddition of azomethine ylide and coumarins is achieved for the synthesis of spiro multi heterocyclic adducts without engaging any catalyst or activator in good yields.

Synthesis and evaluation of the antiproliferative activity of new heterylmethylidene derivatives of imidazothiazolotriazinones

Two series of regioisomeric heterylmethylidene derivatives of imidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazines and imidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazines were synthesized. Several compounds exhibiting high antiproliferative activity were found.