The synthesis and characterization of three new dispiro[indoline-3,3'-pyrrolizine-1',5''-thiazolidine] compounds are reported, together with the crystal structures of two of them. (3RS,1'SR,2'SR,7a'SR)-2'-(4-Chlorophenyl)-1-hexyl-2''-sulfanylidene-5',6',7',7a'-tetrahydro-2'H-dispiro[indoline-3,3'-pyrrolizine-1',5''-thiazolidine]-2,4''-dione, C28H30ClN3O2S2, (I), (3RS,1'SR,2'SR,7a'SR)-2'-(4-chlorophenyl)-1-benzyl-5-methyl-2''-sulfanylidene-5',6',7',7a'-tetrahydro-2'H-dispiro[indoline-3,3'-pyrrolizine-1',5''-thiazolidine]-2,4''-dione, C30H26ClN3O2S2, (II), and (3RS,1'SR,2'SR,7a'SR)-2'-(4-chlorophenyl)-5-fluoro-2''-sulfanylidene-5',6',7',7a'-tetrahydro-2'H-dispiro[indoline-3,3'-pyrrolizine-1',5''-thiazolidine]-2,4''-dione, C22H17ClFN3O2S2, (III), were each isolated as a single regioisomer using a one-pot reaction involving L-proline, a substituted isatin and (Z)-5-(4-chlorobenzylidene)-2-sulfanylidenethiazolidin-4-one [5-(4-chlorobenzylidene)rhodanine]. The compositions of (I)-(III) were established by elemental analysis, complemented by high-resolution mass spectrometry in the case of (I); their constitutions, including the definition of the regiochemistry, were established using NMR spectroscopy, and the relative configurations at the four stereogenic centres were established using single-crystal X-ray structure analysis. A possible reaction mechanism for the formation of (I)-(III) is proposed, based on the detailed stereochemistry. The molecules of (I) are linked into simple chains by a single N-H...N hydrogen bond, those of (II) are linked into a chain of rings by a combination of N-H...O and C-H...S=C hydrogen bonds, and those of (III) are linked into sheets by a combination of N-H...N and N-H...S=C hydrogen bonds.
Keywords: NMR spectroscopy; crystal structure; dipolar cycloaddition; dispiro compound; heterocyclic compound; hydrogen bonding; indoline; molecular conformation; pyrrolizine; supramolecular assembly; synthesis.
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