Protecting Group-Directed Diastereodivergent Synthesis of Chiral Tetrahydronaphthalene-Fused Spirooxindoles via Bifunctional Tertiary Amine Catalysis.

A collection of chiral spirocyclic tetrahydronaphthalene (THN)-oxindole hybrids bearing a quaternary carbon center at the β-position of THN has been developed. The diastereodivergent direct catalytic Michael-aldol reaction between 3-ylideneoxindole and 2-methylbenzaldehyde was accomplished by using bifunctional tertiary amine. Simply changing the protecting group on the substrate in the organocatalytic cascade reaction led to inverted diastereoselectivity in good yields with a high ee value. To explain the diastereodivergence of the organocatalytic Michael-aldol cascade, we also proposed plausible transition-state models for [4 + 2] annulation based on the observed stereochemistry of the products.