A solution of 11.1 g (32.2 millimoles) of ethyl (E)-3-cyclohexyl-2-(ethoxyisobutylphosphinoyl)methylpropenoate in 100 ml of 4.3 N hydrogen chloride-butyl acetate was heated in a sealed tube for 48 hours. After cooling, the solvent was evaporated under reduced pressure to give a mixture of ethyl (Z)-3-cyclohexyl-2-(hydroxyisobutylphosphinoyl)methylpropenoate and ethyl (E)-3-cyclohexyl-2-(hydroxyisobutylphosphinoyl)methylpropenoate as a pale yellow oil. The (Z):(E) ratio determined by 1H-NMR was 90:10. The mixture was dissolved in a mixture of 32 ml of ethanol and 16 ml of 6 N sodium hydroxide, and heated under reflux for 3 hours. After cooling, the solvent was evaporated under reduced pressure. The residue was dissolved in 100 ml of water and made strongly acidic with hydrochloric acid, whereupon crystals precipitated. The crystals were collected by filtration and recrystallized from methanol-water (2:1) to give 4.6 g (yield 49%) of (Z)-3-cyclohexyl-2-(hydroxyisobutylphosphinoyl)methylpropenoic acid. Its melting point and IR and 1H-NMR were identical with those of the product obtained in Example 5 (b).
