A Pd-Catalyzed (6+2) Cycloaddition/Ring-Contraction Relay for Chemodivergent Access to Chiral Spirooxindoles

Herein, we report a Pd-catalyzed asymmetric (6+2) cycloaddition that directly furnishes indole-fused eight-membered lactones bearing an all-carbon quaternary stereocenter with high efficiency and enantioselectivity. Notably, simple modulation of reaction conditions enables chemodivergent skeletal reorganization of these medium-ring lactones. Oxidative conditions trigger ring contraction to deliver seven-membered spirooxindoles, whereas basic conditions selectively afford six-membered spirooxindoles, with both good yields and high diastereoselectivity and enantiospecificity. Moreover, density functional theory calculations were performed to provide mechanistic insight into the (6+2) cycloaddition and the subsequent ring-contraction pathways.