Efficient Synthesis of Dihydrofurans with Sulfide Groups by Ceric(IV) Ammonium Nitrate-Mediated Oxidative Cycloaddition of 1,3-Dicarbonyl Compounds to Vinyl Sulfides. Application to the Synthesis of Benzo[b]naphtho[2,3-d]furan-6,11-dione and First Total Synthesis of Millettocalyxins C and Pongamol Methyl Ether

Ceric(IV) ammonium nitrate-mediated oxidative cycloaddition of 1,3-dicarbonyls to vinyl sulfides afforded substituted dihydrofurans with sulfide groups in moderate yields. This new synthetic method has been applied to the synthesis of benzo[b]naphtho[2,3-d]furan-6,11-dione and furanoflavone natural products such as millettocalyxins C and pongol methyl ether.