Synthesis of Lignan Aryldihydronaphthalene Lactones by Cyclization of Cinnamyl Arylpropiolate Esters: Revised Structure of β-Apopolygamatin

Unlike arylpropargyl arylpropiolates (e.g., 3) which yield, on heating in xylene, arylnaphthalene type I and type II lactones (4 and 5, respectively) in 1:1 ratio, cinnamyl arylpropiolates (e.g., 7) on heating in DMF gave the aryldihydronaphthalene-2-carboxylic acid lactones (e.g., 8) in excellent yield and regioselectivity. It is suggested that the aryldihydronaphthalene lactone product isolated from the tumor-inhibiting extract of Polygala polygama and previously named beta-apopolygamatin [17] has in fact the structure 1-(3',4'-methylene-dioxyphenyl)-3-hydroxymethyl-7,8-dimethoxy-3,4- dihydro-2- naphthoic acid lactone [18].