Dioxindole in Asymmetric Catalytic Synthesis: Routes to Enantioenriched 3-Substituted 3-Hydroxyoxindoles and the Preparation of Maremycin A
作者:Giulia Bergonzini、Paolo Melchiorre
DOI:10.1002/anie.201107443
日期:2012.1.23
nucleophilicity of dioxindole under different reaction conditions is key to a direct and easy access to valuable spiro oxindole γ butyrolactones and 3‐substituted 3‐hydroxyoxindole derivatives in excellent yields and enantioselectivities (see scheme). The preparation of maremycin A serves as an example for the potential usefulness of this previously unexplored reactivity in natural product synthesis.
A 1-hydroxybenzotriazole-assisted, N-heterocycliccarbenecatalyzed direct β-functionalization of saturated carboxylic esters is disclosed. This formal [3 + 2] annulationreaction of carboxylic esters with isatins affords optically pure spirooxindole lactones (on gram scale) bearing two vicinal stereogenic centers. A dual role of HOBt is proposed based on controlled experiments to rationalize the enhancement