3-Ethoxycyclohex-2-ene-1-one → Spiro[2.5]octan-5-one

3-Ethoxycyclohex-2-enone (25 g) was dissolved in diethyl ether (500 mL), and tetraisopropoxytitanium (55 mL) was added, followed by the addition of ethyl magnesium bromide (3.0M in diethyl ether, 180 mL) over 30 minutes. The reaction was stirred at room temperature for another two hours, and quenched by the careful addition of water (250 mL). The mixture was filtered through diatomaceous earth, and rinsed with diethyl ether. The filtrate was transferred to a separatory funnel, the aqueous layer was drawn off, and p-toluenesulfonic acid monohydrate (2 g) was added to the organic layer, which was stirred at room temperature for two days. The reaction mixture was washed with saturated aqueous NaHCO3 and brine, then dried over Na2SO4. The mixture was filtered, and concentrated and chromatography on silica gel using 93/7 hexanes/ethyl acetate provided the title compound.