Structure and Synthesis of Novel C 12 Terpenoids from Quince Fruit ( Cydonia oblonga MILL.)

The structure and synthesis of novel irregular C 12 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.