Asymmetric Synthesis of 3,4-Dihydrocoumarin Motif with an All-Carbon Quaternary Stereocenter via a Michael-Acetalization Sequence with Bifunctional Amine-thiourea Organocatalysts

Asymmetric domino Michael acetalization reactions of 2-hydroxynitrostyrene and 2-oxocyclohexanecarbaldehyde with a bifunctional thioureatertiary-amine organocatalyst, e.g., the Takemoto catalyst, followed by oxidation providing the 1',3-spiro-2'-oxocyclohexan-3,4-dihydrocoumarin having one all-carbon quaternary stereocenter with excellent diastereo- and enantioselectivities (up to >99% ee), are described. The structures and absolute configurations of the products were confirmed by X-ray analysis.