[O:1]1[C:3]2([CH2:14][CH2:13][CH2:12][CH2:11][CH2:10][CH2:9][CH2:8][CH2:7][CH2:6][CH2:5][CH2:4]2)[CH2:2]1.B(F)(F)F.CCOCC.CCCCCC.CCCCCC.C(OCC)(=O)C>CCOCC>[CH:3]1([CH:2]=[O:1])[CH2:14][CH2:13][CH2:12][CH2:11][CH2:10][CH2:9][CH2:8][CH2:7][CH2:6][CH2:5][CH2:4]1To 5.0 g (25.5 mmol) of 1-oxaspiro[2.11]tetradecane in 50 ml of dry ether at 0° C. is slowly added 1.8 ml (2.1 g, 14.6 mmol) of boron trifluoride etherate. The ice bath is removed and after 15 minutes at room temperature the solution is partitioned between ether and saturated sodium bicarbonate. The organic phase is evaporated to give a clear oil. Flash chromatography over silica gel using a hexane to hexane:ethyl acetate (9:1) gradient give 1.6 g (34%) of a clear oil: NMR (CDCl3) δ 1.28-1.8 (m, 18 H), 2.03 (s, 1 H), 2.42 (m, 1 H), 9.62 (s, 1 H)
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