A. (1-Ethenyl)heptanyl 3-ketobutanoate. 3-Hydroxy-1-nonene ((Note 1), 7.5 g, 0.053 mol) is stirred in 250 mL of anhydrous ether (Note 2) in a 500-mL, three-necked, round-bottomed flask, fitted with a thermometer, a nitrogen/mineral oil bubbler, a Teflon-covered magnetic stirring bar, and a rubber septum. A constant flow of nitrogen is maintained throughout the reaction. To this clear homogeneous solution, diketene ((Note 3), 5.04 g, 0.060 mol) is added in one portion by syringe, followed by 4-dimethylaminopyridine (DMAP) (0.591 g, 0.0049 mol, (Note 4)). A slightly exothermic reaction (to 32°C) is observed. After 15 min, the reaction is complete (Note 5). The reaction mixture is quenched with 100 mL of 0.1% sodium hydroxide solution and 100 mL of anhydrous ether. The layers are separated and the organic phase is washed once with 50 mL of 0.1% sodium hydroxide solution and once with brine. Drying over magnesium sulfate and concentration under reduced pressure affords 11.3 g (0.05 mol, 94%) of a pale-yellow oil. The β-keto ester is of high purity, as shown by TLC, GLC, and spectral analyses (Note 6); however, distillation (bp 113–114°C/1.4 mm) leads to a colorless oil.

B. 2-Carboxy-5-dodecen-2-one. A solution of lithium diisopropylamide (LDA, (Note 7)) in 150 mL of tetrahydrofuran (Note 8) is prepared from 0.199 mol (20.12 g) of diisopropylamine (Note 9) and 0.181 mol of butyllithium (Note 10) and (Note 11). The solution is cooled to −78°C (acetone–dry ice) and a solution of 10.0 g (0.044 mol) of (1-ethenyl)heptanyl 3-ketobutanoate in 50 mL of tetrahydrofuran (Note 8) is added via a 12-mL, pressure-equalizing dropping funnel at −78°C over a 15-min period. After the addition is complete, the reaction mixture is stirred at −78°C for 45 min and is then allowed to warm gradually to room temperature. When the reaction mixture finally reaches 25°C (about 2 hr), it has a deep-red color. After the mixture is stirred for 18 hr at room temperature, the reaction is complete (Note 12). To this mixture, 100 mL of water and 100 mL of pentane are added in portions with stirring, maintaining the temperature below 25°C with an ice bath. As the deep-red reaction mixture is quenched, an orange heterogeneous mixture results. The layers are separated and the pentane layer is extracted 2 times with 50 mL of 0.1% sodium hydroxide solution (Note 13). All aqueous layers are combined in a 800-mL beaker equipped with a Teflon-covered magnetic stirring bar. A 100-mL aliquot of pentane is added to this aqueous mixture, which is stirred vigorously, and then 100 mL of 10% hydrochloric acid solution is added in 10-mL portions until pH 2 is reached (Note 14). The heterogeneous solution is poured into a 1-L separatory funnel and the layers are quickly separated. The aqueous layer is extracted 3 times more, each time with 50 mL of pentane. The combined organic layers (ca. 250–300 mL) are dried (MgSO₄), and evaporated at reduced pressure without heating, to give 9.6 g (0.04 mol, 97%) of a red-orange oil. This carboxylic acid is of high purity as shown by TLC and spectral analyses (Note 15).

C. 5-Dodecen-2-one. The 3-carboxy-5-dodecen-2-one (9.0 g, 0.040 mol) is stirred in 150 mL of carbon tetrachloride (Note 16) in a 500-mL, three-necked, round-bottomed flask that is fitted with a reflux condenser, a thermometer, a Teflon-covered magnetic stirrer, and a ground-glass stopper. After the orange-yellow solution is heated at reflux for 1 hr, TLC analysis shows the reaction to be complete (Note 17). The reaction mixture is concentrated under reduced pressure with warming to afford 7.1 g (0.039 mol, 98%) of a red-orange oil. The product is sufficiently pure for most purposes. It may be purified by vacuum distillation at 105–107°C/2.7 mm (5.2 g, 0.03 mol, 71%), which yields a pale-yellow oil (Note 18).