[CH3:1][CH:2]([CH3:8])/[CH:3]=[CH:4]/[C:5]([OH:7])=[O:6].[CH2:9]=[CH:10][CH:11]=[CH:12][CH3:13].CC(C)C=CC(O)=O.S(=O)(=O)(O)O>CCOCC>[CH:2]([CH:3]1[CH:4]([C:5]([OH:7])=[O:6])[CH:12]([CH3:13])[CH:11]=[CH:10][CH2:9]1)([CH3:8])[CH3:1]
A mixture of 70 g (0.61 mol) of trans-4-methyl-2-pentenoic acid and 49 g (0.72 mol) of 1,3-pentadiene was heated for 12 hours at approx. 200° C. in an autoclave. After the reaction mixture had cooled, it was checked by means of GLC for the presence of 4-methyl-2-pentenoic acid. A further 25 g (0.36 mol) of 1,3-pentadiene were added, after which the mixture was again heated for 12 hours at 200° C. This procedure was repeated until no further decrease in the content of 4-methyl-2-pentenoic acid was any longer observed. The reaction mixture obtained was dissolved in 300 ml of ether and extracted with 300 ml of 10% NaOH solution. The alkaline solution thus obtained was acidified with 40 g of concentrated sulphuric acid and then extracted three times with ether. The ether extract was washed with water, dried on MgSO4, evaporated down and distilled. 73 g of 6-isopropyl-2-methyl-3-cyclohexene-1-carboxylic acid were obtained, b.p.: 95°-100° C./70 Pa.
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