Reaction Steps
(5-Ethoxycarbonyl-5-methylhexyl)-triphenylphosphonium bromide (35.0 g, 0.0619 mol) was dissolved in dichloromethane (100 mL) containing 2-chlorobenzaldehyde (8.70 g, 0.0619 mol). A solution of sodium hydroxide (10 g, 0.25 mol) in water (10 mL) was added in portions over ten minutes. The mixture stirred for 2 hours at room temperature. After two hours, the layers were separated and the dichloromethane fraction was washed with water (2×150 mL), dried over sodium sulfate, filtered, and concentrated under reduced pressure. The remaining brown oil (18.99 g) was filtered through silica gel (200 g), eluting with ethyl acetate/heptane (1:9). The product containing fractions were combined and concentrated under reduced pressure. The remaining yellow oil (10.5 g) was contaminated with 2-chlorobenzaldehyde (30-40%). The material was reprocessed by dissolving in fresh dichloromethane (100 mL) with additional phosphonium salt (25 g, 0.048 mol). Sodium hydroxide (10 g, 0.25 mol) in water (10 mL) was added in portions and the mixture was allowed to stir for 4 hours at room temperature. The layers were separated and the dichloromethane fraction was washed with water (2×100 mL), dried over sodium sulfate, filtered, and concentrated under reduced pressure. The remaining brown oil was purified by column chromatography on silica gel (200 g), eluting with ethyl acetate/heptane (1:9). The product-containing fractions were combined and concentrated under reduced pressure to provide 7-(2-chlorophenyl)-2,2-dimethylhept-6-enoic acid ethyl ester (12.0 g, 60% yield) as a light, yellow liquid. 1H NMR (300 MHz, CDCl3/TMS): δ=7.47 (d, 0.4H, J=7.5 Hz), 7.36-7.07 (m, 3.6H), 6.74 (d, 0.4H, J=15.6 Hz), 6.50 (d, 0.6H, J=11.4 Hz), 6.16 (dt, 0.4H, J=15.6, 7.2 Hz), 5.75 (dt, 0.6H, d=11.4, 7.2 Hz), 4.10 (m, 2H), 2.26-2.12 (m, 2H), 1.61-1.34 (m, 4H), 1.29-1.17 (m, 3H), 1.14 (s, 6H). (mixture of cis/trans isomers). 13C NMR (75 MHz, CDCl3/TMS): δ=177.59, 135.63 (2 peaks), 133.67, 133.45, 133.31, 132.38, 130.31, 129.41, 129.19, 127.84, 127.73, 126.57, 126.47, 126.24, 126.00, 60.16, 42.12, 42.07, 40.22, 33.56, 28.83, 25.21, 25.16, 24.69, 14.30. (mixture of cis/trans isomers). HRMS (MMI-TOF): Calculated for C22H29Cl2NO2S (MH+): 406.1202. Found 406.1594.
