[CH3:1][C:2]1[C:6]([CH3:8])([CH3:7])[CH:5]([CH2:9][CH:10]=O)[CH2:4][CH:3]=1.[CH3:12][C:13]([CH2:15][CH3:16])=[O:14].[OH-].[K+].OS(O)(=O)=O>O.CO>[CH3:16]/[C:15](=[CH:10]\[CH2:9][CH:5]1[CH2:4][CH:3]=[C:2]([CH3:1])[C:6]1([CH3:7])[CH3:8])/[C:13](=[O:14])[CH3:12]152 G (1.0 M) of campholenic aldehyde having a purity of about 75% were added dropwise under stirring in 15-20 minutes to a mixture cooled at -5/-10° of 400 g (6.1 M) of methyl-ethyl ketone, 1025 g (35 M) of methanol, 30.5 g (0.54 M) of potassium hydroxide and 380 g of water. The mixture was kept at -5° for 24 hours, then at room temperature for the same period and neutralized thereupon with H2SO4 to 62.5%. After concentration under reduced pressure, the obtained residue was dissolved in 200 ml of water, diluted with petrol ether 30/50, washed until neutrality, dried and concentrated. 189.3 G of a raw material was thus obtained which on distillation with a Vigreux column of 15 cm length gave 144.6 g of (E)-3-methyl-5-(2,2,3-trimethyl-3-cyclopenten-1-yl)-3-penten-2-one having a purity of 86% (yield 60.4%).
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