Hydrochloric Acid → 2,4-Dimethyl-3-cyclohexene carboxaldehyde

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A solution of isopropyl magnesium chloride in ether is prepared by dropwise adding a solution of 164 grams (2.1 moles) of 2-chloropropane in 200 ml of ether to a stirred slurry of 50 grams (2.1 moles) of magnesium in 500 ml of ether at reflux under nitrogen. The resulting solution is stirred at reflux for 30 minutes. A solution of 164 grams (2 moles) of 2,4-dimethyl-3-cyclohexenecarboxaldehyde in 200 ml of ether is added over a 45-minute period to the reaction mixture at reflux under nitrogen. The resulting slurry is heated at reflux for 30 minutes and then cooled to 0° C. 400 ml of 18% aqueous hydrochloric acid is slowly added with cooling and stirring. Two clear layers are formed. The aqueous layer is discarded and the organic layer is washed twice with H2O, neutralizing the second wash with aqueous caustic soda. The ether is removed by distillation at atmospheric pressure. Fractional distillation of the remaining oil (375 grams) through a 11/2"×12" Goodloe packed column affords 121 grams of recovered 2,4-dimethyl-3-cyclohexenecarboxaldehyde; 54 grams of 1,5-dimethyl-3-isopropyl-2-oxabicyclo[2.2.2]octane; and 173 grams of 2,4-dimethylalpha-isopropyl-3-cyclohexene-1-methanol (b.p. 91° C., 2.1 mm Hg pressure).

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