[CH3:1][C:2](=[O:5])[CH2:3][CH3:4].[CH3:6][C:7]12[CH2:12][CH:11]1[CH2:10][CH:9]([CH2:13][CH:14]=O)[C:8]2([CH3:17])[CH3:16].[OH-].[K+].CO>O>[CH3:4][C:3](=[CH:14][CH2:13][CH:9]1[CH2:10][CH:11]2[C:7]([CH3:6])([CH2:12]2)[C:8]1([CH3:16])[CH3:17])[C:2](=[O:5])[CH3:1]560 g (8.5 mol) of butan-2-one and 234 g (1.4 mol) of (1,2,2-trimethyl-bicyclo[3.1.0]hex-3-yl)ethanal were added to 48 g (0.75 mol) of potassium hydroxide dissolved in 500 ml of water and 1.4 1 of methanol. The reaction mixture was stirred overnight with ice-bath cooling, poured into 3 l of water and extracted with diethyl ether. The extract was washed with water, dried (MgSO4) and evaporated in vacuo. The residue was distilled at 108° C./0.1 Torr to give 140 g (45% yield) of 3-methyl-5-(1,2,2-trimethylbicyclo[3.1.0]hex-3-yl)pent-3-en-2-one.
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