Regioselective route for arylnaphthalene lactones: convenient synthesis of taiwanin C, justicidin E, and daurinol

Arylnaphthalene lactones are natural products which can be isolated from a wide range of plants and have the significant biological activities including cytotoxicity, antimicrobial, diuretic, and ion channel blocking. The drawback of the previous intramolecular Diels–Alder reaction of 3-arylprop-2-ynyl 3-arylpropiolates was to generate two regioisomers of arylnaphthalene lactone without selectivity. Herein, we report a convenient and regioselective synthesis method in which the intramolecular Diels–Alder reaction of an arylalkene–arylalkyne and subsequent DDQ oxidation was used for Type I and Type II arylnaphthalene lactones, respectively. We demonstrated the synthesis of three lignans, taiwanin C (Type I), justicidin E (Type II), and daurinol (Type I and anti-cancer activity).