A
1-L, three necked, round-bottomed flask is fitted with a
magnetic stirring bar and a
pressure-equalizing dropping funnel to which is attached an
oil bubbler, a
rubber septum, and an
argon or nitrogen inlet to maintain a static inert gas atmosphere in the reaction vessel throughout the reaction. The flask and dropping funnel are charged with
500 mL of dry methylene chloride and
40 mL (34 g, 0.20 mol) of 1-trimethylsiloxy-1-cyclohexene (Note
1), respectively. The flask is flushed with dry inert gas and immersed in a
cooling bath at ca. −78°C (acetone or 2-propanol-dry ice). Stirring is started and
23 mL (52.1 g, 0.20 mol) of anhydrous stannic chloride (Note
2) is added rapidly through the rubber septum by means of a syringe. Then
20.0 mL (21.0 g, 0.23 mol) of 2-nitropropene (Note
3) is added through the rubber septum by a syringe over a period of 5–10 min, giving a green solution. The reaction mixture is further stirred at −78°C for 20 min, and then the silyl enol ether is added dropwise to the mixture over 1 hr, giving a faint yellow solution. After completion of the addition the resulting solution is stirred at ca. −78°C for an additional hour; then the bath temperature is gradually warmed to −5°C over a period of 3–3.5 hr while the stirring is continued (Note
4). The inert gas flow is stopped, the dropping funnel is replaced by a
condenser, the
magnetic stirrer is removed, and the flask is equipped with a
heating mantle and an
overhead stirring device. Then 280 mL of water are added, and the resulting heterogeneous mixture is vigorously stirred at reflux for 2 hr (Note
5). The mixture is subsequently cooled to room temperature and then poured into a
1-L separatory funnel and the
methylene chloride layer is separated from the water. The aqueous layer is extracted once with
100 mL of methylene chloride, and the combined organic layers are washed twice with 160-mL portions of cold water (Note
6) and once with saturated
brine, dried over anhydrous
magnesium sulfate, and filtered. The solvent is removed on a
rotary evaporator and the residual oil is distilled through a
10-cm Vigreux column under reduced pressure to yield
18.7–21.5 g (
61–70%) of
2-(2-oxopropyl)cyclohexanone as a fragrant yellow liquid, bp
84–85°C (0.8 mm),
nD19 1.4671 [lit.
2 bp
91–93°C (1.1 mm),
nD25 1.4655] (Note
7).