Structure and Synthesis of Novel C12 Terpenoids from Quince Fruit (Cydonia oblonga MILL.)

The structure and synthesis of novel irregular C12 terpenoids isolated from quince fruit (Cydonia oblonga MILL.) are described: quince oxepine (= (E)‐2,3,6,7‐tetrahydro‐4‐methyl‐2‐(3‐methylbuta‐1,3 dienyl)oxepine; 3) and the quince oxepanes as a 1:1 mixture of cis‐ and trans‐isomers (= cis‐ and trans‐(E)‐4‐methyl‐2‐(3‐methylbuta‐1,3‐dienyl)oxepane; 4 and 5, resp.). The absolute configurations of the natural compounds have not been determined due to the minute amounts available, but both relative and absolute configurations of synthetic 4 and 5 were established by chemial correlation with (R)‐pulegone.