[CH3:1][C:2]1([CH3:12])[C:6]([CH3:7])=[CH:5][CH2:4][CH:3]1[CH:8]([CH3:11])[CH:9]=O.CC1C(C)(C)[CH:17]([CH2:21][CH:22]=[O:23])CC=1.C(=O)CC.C[O-].[Na+].[Na]>C(O)(=O)C.CO>[CH3:17][C:21](=[CH:9][CH:8]([CH:3]1[CH2:4][CH:5]=[C:6]([CH3:7])[C:2]1([CH3:12])[CH3:1])[CH3:11])[CH:22]=[O:23]60.0 g (0.36 mol) of 2-(2,2,3-trimethylcyclopent-3-enyl)propionaldehyde, prepared from campholenic aldehyde as known per se, and 42.0 g (0.72 mol) of propanal was added successively during 15 min and 2 hours, respectively, to the sodium methylate solution prepared from 0.83 g of sodium and 200 ml of anhydrous methanol, at 10° C. The reaction mixture was stirred at 10° C. for 2 hours and at room temperature for the following 42 hours. After addition of 5 ml of acetic acid the solvent was evaporated in vacuo at the temperature maintained below 50° C. The residue was diluted with 500 ml of MTBE, washed with 2×200 ml of brine, dried (MgSO4), concentrated in vacuo and distilled at 76-95° C./0.1 Torr to give 28.1 g (38%) of 2-methyl-4-(2,2,3-trimethylcyclopent-3-enyl)pent-2-enal. An analytical sample was prepared by flash chromatography on silica gel (eluent: hexane/MTBE 12:1).
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