Synthesis of spiro[indoline-3,3'-pyrrolizines] by 1,3-dipolar reactions between isatins, L-proline and electron-deficient alkenes.

Two spiro[indoline-3,3'-pyrrolizine] derivatives have been synthesized in good yield with high regio- and stereospecificity using one-pot reactions between readily available starting materials, namely L-proline, substituted 1H-indole-2,3-diones and electron-deficient alkenes. The products have been fully characterized by elemental analysis, IR and NMR spectroscopy, mass spectrometry and crystal structure analysis. In (1'RS,2'RS,3SR,7a'SR)-2'-benzoyl-1-hexyl-2-oxo-1',2',5',6',7',7a'-hexahydrospiro[indoline-3,3'-pyrrolizine]-1'-carboxylic acid, C28H32N2O4, (I), the unsubstituted pyrrole ring and the reduced spiro-fused pyrrole ring adopt half-chair and envelope conformations, respectively, while in (1'RS,2'RS,3SR,7a'SR)-1',2'-bis(4-chlorobenzoyl)-5,7-dichloro-2-oxo-1',2',5',6',7',7a'-hexahydrospiro[indoline-3,3'-pyrrolizine], which crystallizes as a partial dichloromethane solvate, C28H20Cl4N2O3·0.981CH2Cl2, (II), where the solvent component is disordered over three sets of atomic sites, these two rings adopt envelope and half-chair conformations, respectively. Molecules of (I) are linked by an O-H...·O hydrogen bond to form cyclic R66(48) hexamers of \overline{3} (S6) symmetry, which are further linked by two C-H...O hydrogen bonds to form a three-dimensional framework structure. In compound (II), inversion-related pairs of N-H...O hydrogen bonds link the spiro[indoline-3,3'-pyrrolizine] molecules into simple R22(8) dimers.