A. 1-Iodo-3-trimethylsilylpropane. In a dry, 100-mL, two-necked, round-bottomed flask equipped with a magnetic stirring bar, a reflux condenser, and a rubber septum is placed 15.0 g (0.10 mol) of sodium iodide. A nitrogen inlet tube is connected to the top of the reflux condenser and all the apparatus is kept under nitrogen. To this vessel are added 50 mL of acetone and 11.5 mL (10 g, 0.066 mol) of 1-chloro-3-trimethylsilylpropane (Note 1) with a hypodermic syringe through the septum; the resulting white suspension is stirred under reflux for 24 hr. The condenser is replaced with a Claisen head, and the bulk of the solvent is removed under ordinary pressure (Note 2) to give a white slurry. To this is added 60 mL of hexane and the inorganic salts are filtered off by suction. The filter cake is washed with five 10-mL portions of hexane. The hexane is distilled off from the combined organic portions at atmospheric pressure. The residual oil is transferred to a 50-mL, round-bottomed flask fitted with a stirring bar and a Claisen head, and is distilled under reduced pressure to afford 1-iodo-3-trimethylsilylpropane 1 (11.5–13.1 g, 72–81%), bp 84–86°C (25 mm), as a clear liquid (Note 3) and (Note 4).

B. 2-Methyl-2-vinylcyclopentanone. A 300-mL, two-necked, round-bottomed flask fitted with a magnetic stirring bar, a nitrogen inlet tube, and a rubber septum is kept under dry nitrogen. To this flask are introduced 8.3 mL (5.99 g, 0.0591 mol) of diisopropylamine and 120 mL of tetrahydrofuran (Note 5) with a syringe through the septum. The flask is cooled in a dry ice–hexane bath. To the solution is slowly added 38.7 mL of butyllithium (1.53 M in hexane, 0.0592 mol) with a syringe and the mixture is kept at 0°C (in an ice bath) for 10 min. The resulting solution of lithium diisopropylamide is again cooled in a dry ice–hexane bath (−78°C), and 11.2 mL (11.57 g, 0.0645 mol) of N,N'-dimethylpropyleneurea (DMPU) (Note 6) is added. After stirring for 30 min, 6.47 mL (6.15 g, 0.0539 mol) of methyl tiglate is injected drop by drop at −78°C. After the solution is stirred for an additional 20 min, 13.0 g (0.0537 mol) of 1-iodo-3-trimethylsilylpropane 1 is added with a syringe and the dry ice–hexane bath is replaced with an ice bath. The solution is stirred at about 0°C for 1 hr and then poured onto 150 mL of ice-cooled 3 N hydrochloric acid covered with 150 mL of hexane. The organic layer is separated and the aqueous layer is extracted with two 80-mL portions of hexane. The combined organic layers are washed successively with 50 mL of 3 N hydrochloric acid and 50 mL of saturated sodium bicarbonate solution and dried over anhydrous magnesium sulfate. The solvent is removed on a rotary evaporator to afford the crude ester 2 (ca. 13 g) (Note 7), which is sufficiently pure for the next operation.

In a two-necked, round-bottomed flask equipped with a magnetic stirring bar, a rubber septum, and a reflux condenser, the top of which is fitted with a nitrogen inlet tube, is placed 7.3 g (ca. 0.13 mol) of 85% pure potassium hydroxide. To the flask are added 4 mL of water and an ethanol solution (60 mL) of the crude ester 2 (ca. 13 g) with a syringe; the mixture is refluxed for 1 hr. The reflux condenser is replaced with a Claisen head and the bulk of the solvent is distilled off over 30 min (Note 8). The residue is cooled in an ice bath and 80 mL of 6 N hydrochloric acid is cautiously introduced. The mixture is extracted with 150 mL of hexane and the organic layer is separated. To the aqueous layer is added 40 mL of concentrated hydrochloric acid and the solution is again extracted with two 100-mL portions of hexane. The combined organic extracts are dried over anhydrous magnesium sulfate and concentrated under reduced pressure to afford the crude acid 3 (10.6–12.0 g) as a dark-colored oil (Note 9).

A 200-mL, two-necked, round-bottomed flask fitted with a magnetic stirring bar, a reflux condenser, and a rubber septum is flushed with nitrogen. To this flask is introduced a dry benzene solution (50 mL) of crude acid 3 through the septum. Then 8.9 mL (12.9 g, 0.101 mol) of oxalyl chloride is slowly added with stirring at room temperature. After the evolution of gas ceases, the solution is further heated in an oil bath maintained at 70°C for 30 min. The solvent, together with excess oxalyl chloride, is removed at room temperature first on a rotary evaporator and finally with a vacuum pump to leave the crude acid chloride of 3 as a dark-colored oil (Note 10).

In a 300-mL, three-necked, round-bottomed flask fitted with an nitrogen inlet tube, a dropping funnel, and a rubber septum are placed 7.45 g (0.0559 mol) of powdered aluminum chloride and a magnetic stirring bar. After 100 mL of dichloromethane (Note 11) is introduced, the crude acid chloride, dissolved in 50 mL of dichloromethane, is added via the dropping funnel to the stirred suspension of aluminum chloride at 0°C over 5 min, whereupon most of the aluminum chloride dissolves. After further stirring at 0°C for 15 min and at room temperature for 15 min, the flask is recooled in an ice bath and 100 mL of 3 N hydrochloric acid is cautiously added through the dropping funnel. The organic phase is separated and the aqueous layer is extracted 3 times with 50-mL portions of dichloromethane. The combined organic layers are successively washed with 30 mL of 3 N hydrochloric acid and 50 mL of saturated sodium bicarbonate solution, and dried over anhydrous magnesium sulfate. The solvent is removed under ordinary pressure and the residue is distilled under reduced pressure to give 2-methyl-2-vinylcyclopentanone as a clear liquid (3.74–5.6 g, 56–84% yield based on the methyl tiglate), bp 104–124°C (110 mm) (Note 12), ca. 95% pure by GLC (Note 13).