[CH3:1][CH:2]([OH:8])[CH:3]=[CH:4][CH:5]([OH:7])[CH3:6].[CH:9](=O)[CH2:10][CH2:11][CH3:12].C1(C)C=CC=CC=1>C1(C)C=CC(S(O)(=O)=O)=CC=1.O>[CH2:10]([CH:9]1[O:8][CH:2]([CH3:1])[CH:3]=[CH:4][CH:5]([CH3:6])[O:7]1)[CH2:11][CH3:12]A mixture of 580 g (5 moles) of hex-3-ene-2,5-diol, 3 g of p-toluenesulfonic acid, 360 g (5 moles) of n-butanal and 1 l of toluene was refluxed, and the resulting water of reaction (108 ml) was removed in the course of 3 h. Thereafter, the mixture was left to cool to room temperature, 10 ml of a 25% strength aqueous sodium hydroxide solution were added, the mixture was washed neutral with a little water and the toluene was removed under reduced pressure at from 50° to 60° C. The residue obtained was distilled under 0.1 mbar to give 681 g (4 moles) of 2-propyl-4,7-dimethyl-4,7-dihydro-1,3-dioxepin of boiling point 70° C./0.1 mbar.
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