First Synthesis of the Pyrano-Naphthoquinone Lactone (–)-Arizonin C1†
Pyrano-naphthoquinones fused to a γ-lactone ring are structurally and biologically interesting natural products. We have accomplished an enantioselective synthesis of (–)-arizonin C1 (2d) in nine steps. We employed the Sharpless dihydroxylation of β,γ-unsaturated ester 9d as a highly enantioselective (>99 % ee) access to the γ-lactone intermediate 7d. Oxa-Pictet–Spengler cyclization, oxidation, and epimerization as expected led to the conversion of 7d into 2d. The pentasubstituted naphthalene precursor 14 of ester 9d was obtained by Dotz benzannulation.