A. 4-[(E)-1,2-Dichlorovinyl]-4-methyl-2-cyclohexen-1-one (1). A dry, 3-L, one-necked, round-bottomed flask is equipped with a magnetic stirrer and a 500-mL pressure-equalizing dropping funnel. The dropping funnel is fitted with a rubber septum and the air in the system is replaced with dry nitrogen (Note 1). The flask is charged with 1500 mL of anhydrous tetrahydrofuran (Note 2) and 38.9 g (54 mL, 0.38 mol) of diisopropylamine (Note 3). The flask is cooled to 0°C with an ice bath. A 1.51 M hexane solution of butyllithium (255 mL, 0.38 mol) is added dropwise with stirring over a 30-min period. The resulting lithium diisopropylamide is cooled to −78°C with a dry ice-acetone bath (Note 4). A solution of 57.8 g (0.38 mol) of 3-ethoxy-6-methyl-2-cyclohexen-1-one (Note 5) in 400 mL of anhydrous tetrahydrofuran is added dropwise with stirring at −78°C over a 90-min period, followed immediately by the addition of 68 g (66 mL, 0.38 mol) of neat hexamethylphosphoric triamide (Note 6) over a 5-min period. The solution is stirred at −78°C for 45 min, followed by the dropwise addition of 52.6 g (36 mL, 0.40 mol) of neat trichloroethylene (Note 7). The solution is allowed to warm to room temperature slowly over a 6-hr period. As the solution warms, the color changes from pale yellow to olive green, to pale red, and finally to black. After 6 hr (Note 8) the solution is quenched with 1000 mL of water and the organic phase is separated. The aqueous phase is extracted four times with 250 mL of diethyl ether. The organic phases are combined and washed four times with 750 mL of water and twice with 750 mL of brine and dried over magnesium sulfate. The solvent is removed on a rotary evaporator and recovered starting material is removed by fractional distillation at 91–93°C (1 mm) through a 15-cm Vigreux column. The residual crude 6-[(E)-1,2-dichlorovinyl]-3-ethoxy-6-methyl-2-cyclohexen-1-one (Note 9) is dissolved in 400 mL of toluene and placed in a dry, 2-L, one-necked, round-bottomed flask, equipped with a mechanical stirrer; a 500-mL pressure-equalizing dropping funnel is fitted with a rubber septum and the air in the system is replaced with dry nitrogen (Note 1). The solution is cooled to 0°C with an ice bath. A 1 M hexane solution of diisobutylaluminum hydride (400 mL, 0.40 mol) (Note 10) is added dropwise with stirring at 0°C over a 1-hr period. The solution is stirred for 2 additional hr at 0°C. To quench the reaction 200 mL of methanol is carefully added to the stirred reaction mixture, followed slowly at first then more rapidly with 400 mL of water and then 300 mL of 10% sulfuric acid solution. After the mixture is stirred for 10 min, it is transferred to a separatory funnel and 500 mL of 10% sulfuric acid solution is added. The separatory funnel is shaken vigorously for 5 min and the organic phase is separated. The aqueous phase is extracted four times with 300 mL of diethyl ether. The organic phases are combined and washed twice with 300 mL of saturated sodium bicarbonate solution, twice with 300 mL of water, twice with 300 mL of brine, and dried over magnesium sulfate. Solvent removal on a rotary evaporator followed by short-path distillation at reduced pressure affords 31–34 g (40–44%, based on 3-ethoxy-6-methyl-2-cyclohexen-1-one) of 4-[(E)-1,2-dichlorovinyl]-4-methyl-2-cyclohexen-1-one (1) as a colorless oil, bp 75–78°C (0.1 mm) (Note 11).

B. 8-Ethynyl-8-methyl-1,4-dioxaspiro[4.5]dec-6-ene (2). A dry, 1-L, one-necked, round-bottomed flask is equipped with a magnetic stirrer, Dean-Stark trap, and reflux condenser. The flask is charged with 500 mL of benzene, 12.0 g (0.059 mol) of 4-[(E)-1,2-dichlorovinyl]-4-methyl-2-cyclohexen-1-one, 12.2 g (11 mL, 0.20 mol) of ethylene glycol and 40 mg (a catalytic amount) of p-toluenesulfonic acid. After the solution is refluxed for 24 hr, it is poured into 200 mL of saturated sodium bicarbonate solution. The organic phase is separated and the aqueous phase is extracted four times with 50 mL of diethyl ether. The organic phases are combined and washed twice with 100 mL of water and once with 100 mL of brine and are dried over magnesium sulfate. The solvent is removed on a rotary evaporator, and the resulting crude 8-[(E)-1,2-dichlorovinyl]-8-methyl-1,4-dioxaspiro[4.5]dec-6-ene (Note 12) is dissolved in 200 mL of anhydrous tetrahydrofuran and placed in a dry, 1-L, one-necked, round-bottomed flask equipped with a magnetic stirrer and a 500-mL pressure-equalizing dropping funnel. The dropping funnel is fitted with a rubber septum and the air in the system is replaced with dry nitrogen (Note 1). The solution is cooled to −78°C with a dry ice-acetone bath (Note 4). A 1.51 M hexane solution of butyllithium (76 mL, 0.12 mol) is added dropwise with stirring at −78°C over a 30-min period. The solution is stirred at −78°C for 2 hr, the cold bath is removed, and stirring is continued for 90 min. The solution is poured into 100 mL of water and the organic phase is separated. The aqueous phase is extracted four times with 25 mL of diethyl ether. The organic phases are combined and washed twice with 75 mL of water, twice with 75 mL of brine, and dried over magnesium sulfate. Solvent removal on a rotary evaporator followed by short-path distillation at reduced pressure yields 5.5-6.3 g (52–60%) of 8-ethynyl-8-methyl-1,4-dioxaspiro[4.5]dec-6-ene as a colorless oil, bp 88–90°C (1 mm) (Note 13).