Organocatalytic construction of spirooxindole naphthoquinones through Michael/hemiketalization using L-proline derived bifunctional thiourea

Michael/hemiketalization of 2-hydroxy-1,4-naphthoquinone to oxindole ketoester was studied using a series of chiral bifunctional organocatalysts. Good yields (up to 91%) and excellent enantioselectivities (up to 98%) were achieved by using a proline derived thiourea catalyst. This method provides an elegant synthetic route to access oxindole containing naphthoquinone derivatives.