Synthesis of Bis-pyrrolizidine-Fused Dispiro-oxindole Analogues of Curcumin via One-Pot Azomethine Ylide Cycloaddition: Experimental and Computational Approach toward Regio- and Diastereoselection.

Curcumin has been transformed to racemic curcuminoids via an azomethine ylide cycloaddition reaction using isatin/acenaphthoquinone and proline as the reagents. The products were characterized by extensive 1D/2D NMR analysis and single-crystal X-ray crystallographic studies. The enantiomers of one racemic product were separated by HPLC on a Chiralcel OD-H column and were indeed confirmed by the CD spectra of the separated enantiomers.