Diastereodivergent synthesis of novel dispiro(imidazothiazolotriazine-pyrrolidin-oxindoles) based on ortho- and meta-nitrobenzylidene derivatives of imidazothiazolotriazine

Four series of dispiro-fused polyheterocyclic compounds containing spiro(pyrrolidine-2,3′-oxindole) and imidazothiazolotriazine moieties were prepared by [3 + 2] cycloaddition of azomethine ylide to ortho- and meta-nitrobenzylidene derivatives of imidazothiazolotriazine. It was shown that ylide cycloaddition occurs to both diastereotopic faces of the dipolarophiles to give the target compounds as two diastereomers. Skeletal rearrangement of the major dispiro(imidazo[4,5-e]thiazolo[3,2-b][1,2,4]triazine-6,3′-pyrrolidin-2′,3″-oxindoles) (anti-exo-diastereomers) gave isomeric dispiro(imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazine-7,3′-pyrrolidin-2′,3″-oxindoles) (angular syn-exo-diastereomers) that are inaccessible by the direct [3 + 2] cycloaddition reaction.