Novel reactions of ninhydrin oxime with mercaptoalkanoic acids

Ninhydrin oxime and mercaptoalkanoic acids in the presence of trifluoroacetic acid form 2,2′-spiranes incorporating indane-1,3-dione and 3-hydroxy-1,3-thiazolidin-4-one or 3-hydroxytetrahydro-1,3-thiazin-4-one moieties. On heating in acetic anhydride, the same reactants undergo replacement of oxime hydroxy group by sulfur thus affording thiooxime-containing alkanoic acids.