[O:1]=[C:2]([C:18]1[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1)/[CH:3]=[CH:4]/[C:5]([O:7][CH:8]1[CH:13]([CH:14]([CH3:16])[CH3:15])[CH2:12][CH2:11][CH:10]([CH3:17])[CH2:9]1)=[O:6]>CC(C)=O>[O:1]=[C:2]([C:18]1[CH:19]=[CH:20][CH:21]=[CH:22][CH:23]=1)/[CH:3]=[CH:4]\[C:5]([O:7][CH:8]1[CH:13]([CH:14]([CH3:16])[CH3:15])[CH2:12][CH2:11][CH:10]([CH3:17])[CH2:9]1)=[O:6]A solution of 3.0 g (0.009 mole) of (-)-menthyl (E)-4-oxo-4-phenyl-2-butenoate in 100 ml of anhydrous acetone is irradiated with ultraviolet light. After an irradiation lasting 3 hours the solution is evaporated and the residue is recrystallized from n-hexane to give the named compound in a yield of 1.9 g, m.p.: 85°-87° C. [α]D25 =-74.7° (c=1, chloroform).
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