2-Propenoic acid, 3-(4-hydroxy-6-methyl-7-oxabicyclo[4.1.0]hept-1-yl)-,6-[3-(1,1-dimethylethoxy)-3-oxo-1-propenyl]-1-methyl-7-oxabicyclo[4.1.0]hept-3-yl ester