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 thiourea-tertiary-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.