Oxidative Spirocyclization of β-Furyl Amides for the Assembly of Spiro-γ-butenolide-γ-butyrolactones.

The synthesis of heretofore unknown γ-spirobutenolides has been achieved via an m -CPBA-mediated oxidation of β-furyl amides. The reaction employs a tethered amide, ostensibly a poorly reactive carbonyl, as a nontraditional nucleophile resulting in spirolactone formation and concurrent amide cleavage. The transformation exhibits functional group tolerance and compatibility with complex compounds. In situ 1 H NMR spectroscopic studies reveal the identities of key intermediates in the oxidation-spirolactonization-oxidation cascade, suggesting a plausible mechanistic pathway. The distinct diastereofaces of the electrophilic butenolide product may be used for diastereoselective cycloaddition and conjugate addition reactions.