3-Methoxycyclohex-2-en-1-one → Spiro[2.5]octan-5-one

Participants

Reaction Steps

3-Methoxy-cyclohex-2-enone (7.8 g, 61.83 mmol) was dissolved in Et2O (100 mL) and titanium tetraisopropoxide (20.1 mL, 68.01 mmol) was added. To the resulting brown solution ethylmagnesium bromide solution (3M, 60 mL, 180 mmol) was added dropwise over 70 minutes. A precipitate formed over the course of the addition. After 2 hours at RT the now dark brown/black reaction mixture was carefully quenched with saturated aqueous NH4Cl. A dark gray precipitate formed and was filtered off over Celite. The aqueous layer was extracted twice with Et2O. The combined organic layers were washed with brine, dried (Na2SO4), filtered, and evaporated. The residue was taken up in Et2O (100 mL) and p-toluenesulfonic acid monohydrate (0.588 g, 3.091 mmol) was added. The resulting brown solution was stirred at RT over the weekend before being evaporated. The remaining brown oil was purified by SiO2 chromatography (330 g SiO2, hexanes/EtOAc 0 to 7% EtOAc) to give 2.5 g of spiro[2.5]octan-5-one as a light yellow liquid (32% yield).

Provenance & Evidence