2,4-Pentadienoic acid

The intramolecular reaction oF allcenes with various O and N functional groups offers useful synthetic methods for heterocycles[13,14,166]. The reaction of unsaturated carboxylic acids affords lactones by either exo- or endo-cyclization depending on the positions of the double bond. The reaction of sodium salts of the 3-alkenoic acid 143 and 4-alkenoic acid 144 with Li2PdCl4 affords mostly five-membcrcd lactones in 30-40% yields[167]. Both 5-hexe-noic acid (145) and 4-hexenoic acid (146) are converted to five- or six-mem-bered lactones depending on the solvents and bases[168]. Conjugated 2,4-pentadienoic acid (147) is cyclized with Li2PdCl4 to give 2-pyrone (148) in water[i69]. 

The value of a for the trans, tra s-5-substituted 2,4-pentadienoic acids suggests that the conformation in solution is the s-trans (between C and C ). Rough estimates give a value of a of about. 8 for the s-trans and of about 1.0 for... 

The Curtius rearrangement procedure described here is a modification of one reported by Winestock. The submitters have found this procedure to be considerably more reproducible when N,N-diisopropylethylamine is substituted for triethylamine. The procedure described for the preparation of trans-2,4-pentadienoic acid is a modification of an earlier one by Doebner. The submitters have found this method to give reproducibly higher yields, and to be more convenient, than other commonly used procedures for preparing this material. The use of dichloromethane as the extracting and crystallizing solvent greatly simplifies the isolation of polymer-free samples of the crystalline acid. 

Palladium catalyst, 59,160 Palladium(II) chloride, 59,161 Paraformaldehyde, 56,40 Pentachlorophenyllithium, 59, 72 frans-2,4-Pentadienoic acid, 59, 1 2,4-Pentadienoic acids, 59, 6... 

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],... 

Photolytic. The major photolysis and hydrolysis products identified in distilled water were pentachlorocyclopentenone and hexachlorocyclopentenone. In mineralized water, the products identified include cis- and /ra/3s-pentachlorobutadiene, tetrachlorobutenyne, and pentachloro-pentadienoic acid (Chou and Griffin, 1983). In a similar experiment, irradiation of hexachlorocyclopentadiene in water by mercury-vapor lamps resulted in the formation of 2,3,4,4,5-pentachloro-2-cyclopentenone. This compound hydrolyzed partially to hexachloroindenone (Butz et ah, 1982). Other photodegradation products identified include hexachloro-2-cyclopentenone and hexachloro-3-cyclopentenone as major products. Secondary photodegradation products reported include pentachloro-as-2,4-pentadienoic acid, Z- and A-pentachlorobutadiene, and tetrachloro-butyne (Chou et ah, 1987). In natural surface waters, direct photolysis of hexachlorobutadiene via sunlight results in a half-life of 10.7 min (Wolfe et al, 1982). 

The combination of cis-trans isomerism with iso-syndio and erythro-threo dispositions gives complex stractures as exemplified by the 1,4 polymers of 1-or 4-monosubstituted butadienes, such as 1,3-pentadiene (72, 73), and 2,4-pentadienoic acid (74, 75) and of 1,4-disubstituted butadienes, for example, sorbic acid (76). This last example is described in 32-35 (Scheme 6, rotated Fischer projection). Due to the presence of three elements of stereoisomerism for each monomer unit (two tertiary carbons and the double bond) these polymers have been classed as tritactic. Ignoring optical antipodes, eight stereoregular 1,4 structures are possible, four cis-tactic and four trans-tactic. In each series (cis, trans) we have two diisotactic and two disyndiotactic polymers characterized by the terms erythro and threo in accordance with the preceding explanation. It should be noted that here the erythro-threo relationship refers to adjacent substituents that belong to two successive monomer units. 

Desaturation of alkyl groups. This novel reaction, which converts a saturated alkyl compound into a substituted alkene and is catalyzed by cytochromes P-450, has been described for the antiepileptic drug, valproic acid (VPA) (2-n-propyl-4-pentanoic acid) (Fig. 4.29). The mechanism proposed involves formation of a carbon-centered free radical, which may form either a hydroxy la ted product (alcohol) or dehydrogenate to the unsaturated compound. The cytochrome P-450-mediated metabolism yields 4-ene-VPA (2-n-propyl-4pentenoic acid), which is oxidized by the mitochondrial p-oxidation enzymes to 2,4-diene-VPA (2-n-propyl-2, 4-pentadienoic acid). This metabolite or its Co A ester irreversibly inhibits enzymes of the p-oxidation system, destroys cytochrome P-450, and may be involved in the hepatotoxicity of the drug. Further metabolism may occur to give 3-keto-4-ene-VPA (2-n-propyl-3-oxo-4-pentenoic acid), which inhibits the enzyme 3-ketoacyl-CoA thiolase, the terminal enzyme of the fatty acid oxidation system. 

Pentadienoic Acid 2.4-Dichloro-Irifluoro- ElOb, 580 (Educt)... 

Pentadienoic Acide, 2-Benzoyl-amino-2-trifltioromethyl- E10b2. 212 (4.5-H, 1.3-oxazol-Der. + 1I20)... 

The reaction proceeds well with unhindered secondary amines as both nucleophiles and bases. The yield of allylic amine formed depends upon how easily palladium hydride elimination occurs from the intermediate. In cases such as the phenylation of 2,4-pentadienoic acid, elimination is very facile and no allylic amines are formed with secondary amine nucleophiles, while phenylation of isoprene in the presence of piperidine gives 29% phenylated diene and 69% phenylated allylic amine (equation 30).84 Arylation occurs at the least-substituted and least-hindered terminal diene carbon and the amine attacks the least-hindered terminal ir-allyl carbon. If one of the terminal ir-allyl carbons is substituted with two methyl groups, however, then amine substitution takes place at this carbon. The reasons for this unexpected result are not clear but perhaps the intermediate reacts in a a- rather than a ir-form and the tertiary center is more accessible to the nucleophile. Primary amines have been used in this reaction also, but yields are only low to moderate.85 A cyclic version occurs with o-iodoaniline and isoprene.85... 

Stereochemistry is largely lost in die diene vinylation, at least at 100 C, as evidenced by die reaction of (Z,E)-3-methyl-2,4-pentadienoic acid shown in equation (40). 

Pentadienoic acid reacts well with aromatic halides to give 5-aryl-pentadienoic acids. The only vinylic halide studied so far is E-2-bromostyrene. This halide gave a 57% yield of E,E,E-7-phenylheptatrienoic acid.N-(2,4-Pentadienyl)piperidine is very useful... 

Treatment of l,l,l-trichloro-2-penten-4-one with aqueous sodium hydroxide solution gives a good yield of 5-chloro- trans-2- cis-4-pentadienoic acid after standard acid work up. 

Grewe et al (29) synthesised the four possible isomeric acids by stereospecific routes, as also the corresponding piperidides, and determined their spectral and other physical characteristics. This cleared the confusion in earlier works on the supposed isolation of chavicinic acids from pepper. They also determined their pungency and showed that, excepting piperine, 5(3,4-dioxymethylene phenyl)-2-trans.4-trans-pentadienoic acid, all other isomers are poorly pungent. They concluded that neither chavicine nor the other two, cis-trans or trans-cis. isomers exist in natural pepper. They also showed that most of the isomers were unstable to light and were easily converted into the trans.trans piperine. 

The pungency of black pepper [P. nigrum L.) was attributed initially to the presence of piperine only, the structure of which is trans,trans-5-(3,4-methylenedi-oxyphenyl)-2,4-pentadienoic acid piperidide. Further investigations into the pungency of this spice by several workers led to the discovery that materials other than piperine also contributed to its pungency (Traxler, 1971). 

Piperine is a yellow crystalline substance having a melting point of 128—130°C. Piperine, C17H1903N, was shown to be a weak base which, on hydrolysis with aqueous alkali or nitric acid, yielded a volatile base CjH N, later identified as piperidine. The acidic product of hydrolysis, piperine acid (C12H1904, m.p. 216-217°C), was shown to be 5-(3,4-methylene dioxy phenyl)-2,4, pentadienoic acid. 

Similarly, Morokuma located four transition states (9-12) for the Diels-Alder cyclization of acrylic acid with 2,4-pentadienoic acid. These transition states are shown in Figure 4.6. All show rather large asynchronous bond formation, with a difference in the new o-bond distances of as much as 0.5 Al... 

When the acylcobalt species is derived from a compound containing halogen on an activated carbon (e.g. an a-halo ester or nitrile) an elimination may occur to introduce an exocyclic double bond in the final product. This sequence, leading to lactones of pentadienoic acids, is general for both terminal and internal alkynes in the presence of amine bases (equation 17). ... 

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