C s-Cinnamic acids

Recall from Section 7.13 that a stereospecific reaction is one in which each stereoisomer of a particular starting material yields a different stereoisomeric form of the reaction product. In the examples shown, the product from Diels-Alder cycloaddition of 1,3-butadiene to c/s-cinnamic acid is a stereoisomer of the product from trans-cinnamic acid. Each product, although chiral, is formed as a racemic mixture. 

Z-Isomerizations in the crystalline state are apparently difficult processes. Effectively, an internal rotation of 180° must occur. However, crystals are usually closely packed. Nevertheless, several examples have been found for such processes and those are 12 c/s -cinnamic acids 23 [36], the ds-isomer 24 [30a], the trans-compounds 25 and 26 [29], the ds-compound 27 [37], and the nonphotocyclizingchalcones 29 and 30 [38], In most cases (except 25 and 26) the products appear to be less sterically hindered and the reactions irreversible in the solid. Mechanistic assumptions made with 23 and 27... 

The high instability of bromine monochloride (the heat of formation of which has been estimated as 0.3 kcal.mole ) provides some difficulty in studying its reactions. Nonetheless, the rate of addition of mixtures of chlorine and bromine (with the total concentration of halogen constant) to c/s-cinnamic acid in carbon tetrachloride-acetic acid mixtures was greatest when [Br2]/[Cl-i] was unity . The kinetic form of the reaction was the same as that for the other interhalogens and for bromine, but not for chlorine. The possible intervention of bromine monochloride in the reaction of allyl trimethylammonium perchlorate with hypobromous acid in aqueous acid has also been reported here, the kinetics were . 

The addition of benzonitrile oxide to acrylic acid gave only the 4-carboxylic acid (441) (59MI41601), while addition to cis- and trans-cinnamic esters gave cis and trans diastereomeric pairs of 4-carboxylic acids (442) (Scheme 100) (59MI41600). Arbisono repeated the experiment and, when methyl c/s-cinnamate was used, in addition to the 4-carboxylic acid some 5-carboxylic acid (442) was isolated (66MI41600). The reaction of vinyl bromides with benzonitrile oxide yielded only an isoxazole and not a bromoisoxazoline (Scheme 101) (78JCR(S)192). 

Quinic Acid trans-Cinnamates Only (+)-Quinic Acid trans- and c/s-Cinnamates of Quinic Acid trans-Cinnamates Only... 

The sensitivity to temperature is reminiscent of that seen in Ron s study (188) of o-methoxy-m-cinnamic acid, 129. When crystals of this substance are exposed to light at low temperatures (< — 80°C), there occurs a gradual isomerization of the molecules to the trans form, 130, with formation of a little of the (2 + 2) photodimer, 131, of the latter. If this irradiated material is warmed in the dark to + 60°C, recooled, and reirradiated for a short while, there is a jump in the amount of dimer. This behavior is interpreted as follows ... 

Conversion of frans-cinnamic acids into the c/s-isomers (Table 8.12)... 

El-Basyouni, S.Z., A. C. Neish, andG. H. N. Towers The Phenolic Acids in Wlxeat III. Insoluble Derivatives of Phenolic Cinnamic Acids as Natural Intermediates in Lignin Biosynthesis. Phytochem. 3, 627—640 (1964). 

DC040 Sarkar, S., and C. T. Phan. Some hydroxy-cinnamic acids of the carrot root. Plant Sci Lett 1974 2 41. 

Houpis, I.N., Patterson, L.E., Alt, C.A., Rizzo, J.R., Zhang, T.Y. and Haurez, M. S3mthesis of PPAR Agonist via Asymmetric Hydrogenation of a Cinnamic Acid derivative and Stereo-specific Displacement of (S)-2-Chloropropionic Acid. Org. Lett. 2005, 7, 1947-1950. 

Lee S-H, Mendenhall GD (1988) Relative yields of excited ketones from self-reactions of alkoxyl and alkylperoxyl radical pairs. J Am Chem Soc 110 4318-4323 Leitzke A, Reisz E, Flyunt R, von Sonntag C (2001) The reaction of ozone with cinnamic acids - formation and decay of 2-hydroperoxy-2-hydroxy-acetic acid. J Chem Soc Perkin Trans 2 793-797 Lodhi ZH, Walker RW (1991) Oxidation of allyl radicals kinetic parameters for the reactions of allyl radicals with H02 and 02 between 400 and 480 °C. J Chem Soc Faraday Trans 87 2361-2365 Martini M, Termini J (1997) Peroxy radical oxidation of thymidine. Chem Res Toxicol 10 234-241... 

Figure S.21 Resulting chromatogram at the optimum conditions predicted by figure S.20. pH = S.8 concentration of n-octylamine = 3.2 mM. ODS column mobile phase methanol-water (20/80) with 0.010 M acetate buffer. Solutes E = phenylethylamine, P = phenylalanine, V = vanillic acid, C = trans caffeic acid, M = trans p-coumaric acid, F = trans ferulic acid, A = phenylacetic acid, H = hydrocinnamic acid and N = trans cinnamic acid. Figure taken from ref. [559]. Reprinted with permission. 

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