Br[CH2:2]/[CH:3]=[CH:4]/[C:5]([O:7][CH2:8][CH3:9])=[O:6].[Na].[CH2:11]([O:13][P:14]([CH:19]([CH3:25])[C:20]([O:22][CH2:23][CH3:24])=[O:21])([O:16][CH2:17][CH3:18])=[O:15])[CH3:12].[H-].[Na+]>O1CCOCC1>[C:5]([CH:4]=[CH:3][CH2:2][C:19]([P:14]([O:13][CH2:11][CH3:12])([O:16][CH2:17][CH3:18])=[O:15])([CH3:25])[C:20]([O:22][CH2:23][CH3:24])=[O:21])([O:7][CH2:8][CH3:9])=[O:6]Ethyl 4-bromocrotonate (19.3 parts) was added dropwise at 25°-30° C. to a solution of the sodium salt of ethyl 2-diethylphosphonopropionate, prepared from 23.8 parts of ethyl 2-diethylphosphonopropionate and 5.3 parts of sodium hydride (50% in oil) in dioxan. The resulting solution was heated at reflux for 18 hr., after which time the sodium bromide was removed by filtration and the solution concentrated in vacuo. The residual oil was distilled to give 12.7 parts of ethyl 5-carboethoxy-2-diethylphosphono-2-methylpent-4-enoate boiling at 158°/0.2 mm. Hydrogenation of 12 parts of this material over 5% palladium on carbon gave 7.2 parts of diethyl 2-diethylphosphono-2-methyladipate boiling at 146°-52° C./0.05 mm; subsequent hydrolysis of 5 parts of this in concentrated hydrochloric acid gave 3.7 parts of 2-methyl-2-phosphonoadipic acid as a glassy solid which had a 31P chemical shift of -24 ppm.
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