Sulfuric Acid → 1-Methyl-3-(2-methylpropyl)-2-oxabicyclo[2.2.2]octane

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A solution of isobutyl magnesium bromide in ether is prepared by dropwise adding a solution of 517 grams (3.45 moles) of 1-bromo-2-methyl propane in 700 ml of dry ether to a stirred slurry of 76.5 grams of magnesium (3.15 moles) in 600 ml of dry ether under nitrogen at reflux. The resulting solution is stirred at reflux for 30 minutes. A solution of 372 grams of 4-methyl-3-cyclohexenecarboxaldehyde (3.38 moles) in 200 ml of ether is then added to the reaction mixture over a period of one hour at reflux under nitrogen. The resulting slurry is heated at reflux for 30 minutes and then cooled to 0° C. 1200 grams of 20% sulfuric acid is slowly added with external cooling over a 30-minute period. After the addition is complete, two clear layers appear. A distillation head is placed on the flask and ether is distilled from the reaction mixture at atmospheric pressure to a pot temperature of 90° C. 500 ml of water and 300 ml of isopropyl alcohol is added to the reaction mixture. Sulfuric acid (200 grams) is added slowly and the resulting solution is heated to reflux for 9 hours. At the end of this period, the reaction is cooled. 500 ml of water and 200 ml of toluene is added thereto with stirring. The phases are allowed to separate and the aqueous phase is discarded. The organic phase is washed twice with H2O with sufficient sodium carbonate added to the second wash to adjust to pH to 7-8. Distillation of the organic layer affords 220 grams (1.2 moles) of 1-methyl-3-(2-methylpropyl)-2-oxabicyclo[2.2.2]octane. Fractionation through a 1.5"×12" Goodloe column affords the pure compound (b.p. 62° C., 2.00 mm Hg pressure).

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