[CH2:1]([O:3][C:4](=[O:15])[CH:5]=[C:6]([CH3:14])[CH:7]=[CH:8][CH:9]=[C:10]([CH3:13])[CH2:11]O)[CH3:2].CCOCC.P(Br)(Br)[Br:22]>N1C=CC=CC=1.CCCCCC>[CH2:1]([O:3][C:4](=[O:15])[CH:5]=[C:6]([CH3:14])[CH:7]=[CH:8][CH:9]=[C:10]([CH3:13])[CH2:11][Br:22])[CH3:2]36.5 g. of 8-hydroxy-3,7-dimethyl-octa-2,4,6-trien-1-oic acid ethyl ester are dissolved in 380 ml. of ether. The solution is cooled to 0° C., and after the addition of 3 drops of pyridine treated dropwise with 28.6 g. of phosphorous tribromide in 120 ml. of hexane. The mixture is stirred for 20 minutes at 0° C., then poured onto ice water and extracted with ether. The ether extract is washed successively with water, a saturated aqueous sodium bicarbonate solution and again with water, dried over sodium sulfate and evaporated. There is obtained 8-bromo-3,7-dimethyl-octa-2,4,6-trien-1-oic acid ethyl ester, which is processed as follows:
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