Structural elucidation of adducts formed by ninhydrin with indoles and thiourea by 13C-NMR spectroscopy.

Condensation products were prepared by the reaction of ninhydrin with indole and 2,5-dimethylindole. The structures of these 1:1 adducts were assigned as 3-(2-hydroxy-2-indane-1,3-dionyl)indole and 3-(2-hydroxy-2-indane-1,3-dionyl)-2,5-dimethylindole, respectively, on the basis of spectral data including 13C-NMR evidence. 13C-NMR also was used to confirm the structure of a thiourea-ninhydrin adduct as a substituted thioindeno[1,2-d]imidazole-2,8-dione.