IDENTIFICATION OF NEW CONSTITUENTS OF QUINCE FRUIT FLAVOR (CYDONIA-OBLONGA MILL = CYDONIA-VULGARIS PERS)

As a flavor of quince fruit, four new bicyclo[4.3.0]nonanes, 2,2,6,7-tetramethylbicyclo[4.3.0]nona-4,7,9(1)-triene (1), (+)-2,2,6,7-tetramethylbicyclo[4.3.0]nona-4,9(1)-dien-8-one (2), (-)2,2,6,7-tetramethylbicyclo[4.3.0]nona-4,9(1)-diene-7,8-diol (3), and (-)2,2,6,7-tetramethylbicyclo[4.3.0]nona 4.9 (1)-dene-7,8-diol (4), have been identified. Racemic compounds 1-4 have been synthesized from 4-oxoisophorone by direct and regioselective reduction to 4-hydroxy-2,6,6-trimethyl-2-cyclohexen-1-one followed by ketal Claisen rearrangement. 3,4-Didehydro-.beta.-ionol (5) has also been found to be one of the constitutents of quince fruit oil.