[CH2:1]1[C:3]2([CH2:12][CH2:11][C:6]3(OCC[O:7]3)[CH2:5][CH2:4]2)[CH2:2]1.[OH-].[Na+].C([O-])(O)=O.[Na+]>C1COCC1.O.C(O)(C(F)(F)F)=O>[CH2:2]1[C:3]2([CH2:12][CH2:11][C:6](=[O:7])[CH2:5][CH2:4]2)[CH2:1]1A solution of 7,10-dioxa-dispiro[2.2.4.2]dodecane (6.25 g, approx. 29 mmol) in THF (25 mL), water (20 mL) and TFA (10 mL) is stirred at rt for 2 h. The mixture is neutralized by adding 2 N aq. NaOH and sat. NaHCO3 solution and extracted with diethyl ether. The organic extracts are washed with water, dried over Na2SO4, filtered and the solvent of the filtrate is removed to give spiro[2.5]octan-6-one (5.0 g) as a colourless oil containing remainders of toluene (product volatile). 1H NMR (CDCl3): δ 2.14 (t, J=6.4 Hz, 4H), 1.40 (t, J=6.4 Hz, 4H), 0.21 (s, 4H).
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