Regio- and stereospecific assembly of dispiro[indoline-3,3′-pyrrolizine-1′,5′′-thiazolidines] from simple precursors using a one-pot procedure: synthesis, spectroscopic and structural characterization, and a proposed mechanism of formation

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.