[CH3:1][C:2]1([CH3:12])[C@H:7]2[CH2:8][C@@H:3]1[CH2:4][CH:5]=[C:6]2[CH2:9][CH2:10][OH:11].[O:13]1[CH:18]=[CH:17][CH2:16][CH2:15][CH2:14]1.Cl.[OH-].[Na+]>Cl.ClCCl>[O:13]1[CH2:18][CH2:17][CH2:16][CH2:15][CH:14]1[O:11][CH2:10][CH2:9][C:6]1[C@@H:7]2[CH2:8][C@H:3]([CH2:4][CH:5]=1)[C:2]2([CH3:12])[CH3:1]
A solution of 2-{(1R,5S)-6,6-dimethylbicyclo[3,1,1]hept-2-en-2-yl}ethanol (61.6 g) in a minimum of dichloromethane (20 ml) was acidified by treatment with concentrated hydrochloric acid (2 drops). The solution was then treated with 2,3-dihydropyran (56 g), dropwise, at such a rate that the temperature rose to 60° C. and remained at 60° C. During the addition of the 2,3-dihydropyran the acidic nature of the mixture was maintained by the addition of one or more further small quantities of concentrated hydrochloric acid. The mixture was stirred at 60° C. for a further period of 3 hours, and was then added dropwise to a vigorously stirred, ice-cooled, aqueous sodium hydroxide solution (2 N; 91 ml). The resulting mixture was extracted with diethyl ether and the ethereal extract was dried over sodium sulphate, and concentrated and distilled in vacuo, to give 2-{(1R,5S)-6,6-dimethylbicyclo[3,1,1]hept-2-en-2-yl}ethyl tetrahydropyran- 2-yl ether (74 g), b.p. 160°-167° C./14 mmHg [νmax (liquid film): 978, 998, 1038 cm-1. N.M.R. (10% w/v solution in deuterochloroform): multiplets at 5.3δ, 4.55δ, 2.25δ, 1.6δ, broad multiplet at 3.6δ, singlets at 1.3δ, 0.83δ. C16H26O2 requires C, 76.75%; H, 10.47%; found C, 76.75%; H, 10.6%].
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