Carbon Dioxide → 3-Butenal, 2-methyl-4-(2,6,6-trimethyl-2-cyclohexen-1-yl)-

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A mixture of 192 g of α-ionone, 165.4 g of ethyl chloroacetate, 500 mg of phenothiazine and 100 ml of pyridine is treated with 81 g of sodium methylate within 30 minutes at -10° C to -15° C with the exclusion of moisture and oxygen from the air. After the addition of 100 ml of absolute ether, the mixture is stirred for 4 hours at - 5° C and treated with 400 ml of 15% methanolic sodium hydroxide while cooling. The mixture is stirred for 1 hour at 10° C, cooled to -30° C and adjusted to a pH of about 4 by the addition of 600 ml of glacial acetic acid. After warming to room temperature, 1 liter of water is added and the mixture stirred again for 15 minutes (CO2 evolution). Extraction with hexane, washing the organic phase neutral, drying over anhydrous sodium sulphate and removal of the solvent under reduced pressure yields 190 g of a brown, liquid crude product which is subjected to fractional distillation in vacuo and produces 125 g of 2-methyl-4-(2,6,6-trimethyl-2-cyclohexenyl)-3-butenal; b.p.0.15 = 90° C; nD20 = 1.4880. Odour: woody, ionone-like, flowery.

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