反应详情

4.7 g (0.202 mol) of magnesium shavings in a 3-necked flask under an argon atmosphere and provided with a calcium chloride tube are activated by addition of 2.0 ml of methyl iodide. After 5 minutes, the methyl iodide is removed and the magnesium washed several times with absolute tetrahydrofuran. To the activated magnesium is added dropwise a solution of 44 g (0.175 mol) of 2-[(S)-4-bromo-3-methylbutoxy]-tetrahydro-2H-pyran in 50 ml of absolute tetrahydrofuran at such a rate that the solvent just boils. Where the Grignard reaction does not start itself, it is warmed to 85° with the oil bath. After completed addition of 2-[(S)-4-bromo-3-methylbutoxy]-tetrahydro-2H-pyran, the mixture is stirred at 85° for so long (0-15 min.) until only traces of 2-[(S)-4-bromo-3-methylbutoxy]-tetrahydro-2H-pyran are still present in accordance with gas-chromatographical analysis. The solution obtained is cooled to -78° and treated dropwise with 21.2 g (0.0875 mol) of 3-methyl-1-butanol-p-toluenesulphonate followed by 3.6 ml of a 0.1 molar solution of Li2CuCl4 in absolute tetrahydrofuran. This reaction mixture is stirred at -78° during 10 min. then at 0° for 2 hours and subsequently at room temperature for a further 14 hours. For the working up of the 2-[(R)-3,7-dimethyloctanoxy]-tetrahydro-2H-pyran obtained the mixture is poured on to ice and brought to pH 5-6 with 2-N sulphuric acid. By three-fold extraction with ether and removal of the solvent on the rotary evaporator there is obtained a mixture of (R)-3,7-dimethyl-1-octanol and 2-[(R)-3,7-dimethyloctanoxy]-tetrahydro-2H-pyran. This mixture is treated portionwise in 100 ml of methanol at 0° with a total of 100 ml of 7-N aqueous hydrochloric acid. After 2-hours stirring at room temperature, the mixture is neutralised with dilute aqueous caustic soda and extracted with ether. After chromatography on silicagel, deactivated with 0.5% ammonia, with pentane/ether (4:1), there are obtained 10.6 g (76% based on 3-methyl-1-butanol-p-toluenesulphonate employed) of pure (R)-3,7-dimethyl-1-octanol. B.p. 58°-59°/0.05 Torr; [α]D20 = +4.0 (c = 1.03, CHCl3).

1. customthe methyl iodide is removed
2. customWhere the Grignard reaction
3. temperatureis warmed to 85° with the oil bath
4. customThe solution obtained
5. temperatureis cooled to -78°
6. waitat 0° for 2 hours
7. waitsubsequently at room temperature for a further 14 hours