Construction of an Epoxy-lactone Moiety on the C/D Ring of Highly Oxygenated Triterpenes through a Modified SeO2-Promoted Oxidative Cyclization

Abstract We present herein a synthetic endeavor to prepare the epoxy-lactone moiety commonly present in the C/D ring of highly oxygenated triterpenes. Two strategies are applied starting from ursolic acid­: (i) Br+-promoted cyclization–isomerization for late-stage epoxidation, and (ii) one-step SeO2-promoted oxidative cyclization. Additionally, the desired epoxy-lactone moiety can be readily prepared on gram scale in one step by using the modified SeO2/TBHP/AcOH oxidative system.