Pentadienoic hydrogenation

Another alternative method to produce sebacic acid iavolves a four-step process. First, butadiene [106-99-0] is oxycarbonylated to methyl pentadienoate which is then dimerized, usiag a palladium catalyst, to give a triply unsaturated dimethyl sebacate iatermediate. This unsaturated iatermediate is hydrogenated to dimethyl sebacate which can be hydrolyzed to sebacic acid. Small amounts of branched chain isomers are removed through solvent crystallizations giving sebacic acid purities of greater than 98% (66). 

A complex naturally occurring amino acid 5-hydroxypiperazic acid (5HyPip) 100 was prepared by a multistep procedure that included Diels-Alder addition of 2,4-pentadienoic acid to phthalazinedione 83a as a first step (Scheme 24). Adduct 97 was esterified and oxidized with mercuric acetate to 98, which on hydrogenation over rhodium on alumina and subsequent hydrolysis provided a mixture of enantiomers from which the required enantiomer 99 was obtained by resolution with quinine. Its hydrazinolysis provided 100 [71JCS(C)514 77H119],... 

Isosteric substitution of the C-2 hydrogen atom of valproic acid (12) with a fluorine atom affords 2-fluorovalproic acid (22), which causes significantly less hepatoxicity than valproic acid, although a reduction in anticonvulsant properties is also observed [59, 60]. The hepatoxicity of 12 involves hepatic cytochrome P450-mediated metabolism to its 4-ene metabolite (14), which undergoes further metabolism, specifically mitchondrial (3-oxidation, to provide ( )-2-propyl-2,4-pentadienoic add (23), a reactive electrophilic metabolite [59, 60]. 

Addition of hydrogen is selective for the double bond further from the electron-withdrawing group thus, the major alkene formed on selective reduction of ethyl 4-methyl-2,4-pentadienoate is the a,/3-unsaluralcd ester (equation 1). The reaction proceeds under mild conditions and in the presence of oxygen. 

In pentadienoic acid and sorbic acid, the double bond next to the carbonyl group is harder to hydrogenate. Thus pentadienoic acid and sorbic acid can be hydrogenated in the presence of Pd, in ethanol at RT and atm P to conjugated 2-pentanoic acid and 2-hexenoic acid . The conjugated diene moiety may be totally reduced in the presence of other double bonds properly substituted, e.g., hydrogenation of the sesquiterpene aldehyde sinensal, IS, over Pt oxide stops after selective saturation of the conjugated diene ... 

Hydrogenation of 2,4-pentadienoic acid was carried out analogously The acid (29.5 g) was dissolved in purified methanol (100 ml), and Adams catalyst (0.25 g) was added. 3-Pent-enoic acid distilled at 93°/15 mm. The yield was almost quantitative. In this hydrogenation, also, the reaction was interrupted after absorption of 1 equivalent (0.602 g) of hydrogen in 20 min. 

---