Trans 2,4-Pentadienoic acid

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. 

A. trans-2,4-Pentadienoic acid. A 1-1., three-necked, round-bottomed flask is equipped with a mechanical stirrer, a condenser cooled with ice-cold water (Note 1) and bearing a calcium chloride drying tube, and a powder funnel. The flask is charged with 206 g. (210 ml., 2.6 moles) of pyridine (Note 2), vigorous stirring is... 

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 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 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. 

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. 

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). 

Various trans-1-iV-acylamino-1,3-butadienes (58) are prepared from 2,4-pentadienoic acids (57) by the mixed anhydride method (equation 37). The procedure is reproducible when V,V-diisopropylethyl-amine is used in place of triethylamine. 

To understand how to control process conditions to give methyl, 4-pentadienoate, the reaction mechanism must be examined. (See Equation 2.). -palladium hydride elimination from 4 gives rise to trans and cis-methyl penta-, 4-dienoate which is the desired monocarbonylation intermediate for sebacic acid. The desired mono-carbonylation reaction is promoted by low carbon monoxide pressure ( 1000 psig) while high pressure (1800 psig) gives excellent 1,4-dicarbonylation product yield. The mono-carbonylation reaction is also facilitated by using a Lewis Acid as a co-catalyst and iodide as the preferred palladium counter-ion (Table III.). Chloride is the preferred palladium counter-ion for 1,4-dicarbonylation. 

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