Cinnamic decarboxylation

Reactions. Heating an aqueous solution of malonic acid above 70°C results in its decomposition to acetic acid and carbon dioxide. Malonic acid is a useful tool for synthesizing a-unsaturated carboxyUc acids because of its abiUty to undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic acids are formed from the reaction of malonic acid and benzaldehyde derivatives (1). If aUphatic aldehydes are used acryhc acids result (2). Similarly this facile decarboxylation combined with the condensation with an activated double bond yields a-substituted acetic acid derivatives. For example, 4-thiazohdine acetic acids (2) are readily prepared from 2,5-dihydro-l,3-thiazoles (3). A further feature of malonic acid is that it does not form an anhydride when heated with phosphorous pentoxide [1314-56-3] but rather carbon suboxide [504-64-3] [0=C=C=0], a toxic gas that reacts with water to reform malonic acid. 

For cinnamic acid at 9.6 °C, a = 0.107, b = 1.25 and k = 0.69 l.mole .sec E = 26.7 0.5 kcal.mole" and AS = 34.5 eu. Identification of products of oxidation of a number of acids indicates two concurrent mechanisms. Predominating is direct attack on the double bond to give, ultimately, cleavage products, e.g. benzaldehyde from cinnamic acid (some phenylacetaldehyde is also found, indicating oxidative decarboxylation to occur) and also acetophenone from 3-phenylcrotonic acid. 

A number of carboxylic acids are found in nature and also present in metabolic pathways. Accordingly, if monobasic acids are smoothly decarboxylated, they are expected to provide us with new routes to supply useful materials for chemical industry without depending on petroleum. Actually, there are some already known examples. The representative examples are the decarboxylation of cinnamic acid derivatives (Table 8). ... 

Although the reaction mechanism of this type of reactions is not fully elucidated, it is easily anticipated that no intramolecular special stabilization effect for the carbanion generated from decarboxylation is expected, different from the case of malonic acid-type compounds. Moreover, cinnamic acid derivatives that have both the electron-donating and withdrawing substituents have been reported to undergo this reaction. This fact suggests that the enzyme itself stabilizes the transition state without the aid of mesomeric and inductive effects of the other part of the substrate molecule itself. If such unknown mechanism also works for other... 

Lindsay RF, FG Priest (1975) Decarboxylation of substituted cinnamic acids by enterobacteria the influence on beer flavour. J Appl Bacterial 39 181-187. 

The chiral center would be installed from either Unear carbamate 15 or branched carbamate 16 via the asymmetric addition of malonate anion to the 7i-allyl Mo complex reported by Trost et al. [11] to afford the branched chiral malonate derivative 17. Decarboxylation of 17 should provide the mono-carboxylic acid 18. Masa-mune homologation with 18 affords our common precursor 14. Linear carbamate 15 was obtained from the corresponding cinnamic acid, and branched 16 was prepared in one pot from the corresponding aldehyde. 

Landete and others (2009) reported that Lactobacillus plantarum have the ability to metabolize phenolic compounds found in olive products (such as oleuropein, hydroxytyrosol, and tyrosol, as well as vanillic, p-hydroxybenzoic, sinapic, syringic, protocatechuic, and cinnamic acids). For example, oleuropein was metabolized mainly to hydroxytyrosol, whereas protocatechuic acid was decarboxylated to catechol by the enzymatic actions. 

Research Focus Method of preparing 4-hydroxystyrene by de-carboxylation of 4-hydroxylcinnamic acid for use in preparing poly(4-glycidyloxystyrene). Originality While the thermal decarboxylation of cinnamic acid as a method of... 

Xanthones in higher plants are also formed by this mixed pathway, though the polyketide chain originates from a benzoic acid instead of the usual cinnamic acid. Cyclization now affords a benzophenone (691), rather than a chalcone, which subsequently cyclizes to the xanthone, a route used with considerable success in the laboratory (Scheme 280). Other xanthones are derived only from acetate, through ring opening, decarboxylation and cyclization of an anthraquinone precursor. 

A pure culture of the organism was inoculated into a basal medium with the addition of 0.025% caffeic acid. After 7 days incubation at 25°C under conditions of reduced oxygen tension, the caffeic acid was completely metabolized. Metabolites of caffeic acid are identified as dihydrocaffeic acid and ethyl catechol, respectively. In the 1960s, it has been reported that a constitutive enzyme present in strains of Aerobacter decarboxylates caffeic acid to 4-vinylcatechol nonoxidatively [20], Several cinnamic acids have been tested and the decarboxylation product from /7-coumaric acid has been identified as 4-vinylphenol. Thus, the bacterial enzyme activity requires a relatively unhindered 4-hydroxy group on the aromatic ring and an acrylic acid side chain. 

Reactions. Malonie acid is a useful tool lor synthesizing a-unsaturaled carboxylic acids because of its ability lo undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic... 

If the original reaction is carried out under more vigorous conditions with malonic acid 67, the decarboxylation occurs during the reaction to give the unsaturated acid in one step. This is a simple way to make11 substituted cinnamic acids 68. 

Malonic acid itself can react with aldehydes in the presence of piperidine by way of a Knoevenagel condensation. A decarboxylation occurs after the condensation, and this decarboxylation cannot be avoided. Figure 13.55 shows how the overall reaction can be employed for the synthesis of cinnamic or sorbic acid. This reaction sequence occurs under much milder conditions than the Perkin synthesis of cinnamic acids. (The Perkin synthesis consists of the condensation of aromatic aldehydes with acetic acid anhydride in the presence of sodium acetate.)... 

Precursors. Both hydroxycinnamic acids and 4-vinylphenols can lead to the formation of hydroxyphenyl-pyranoanthocyanins. The main hydroxycinnamic acids present in wines are p-coumaric, caffeic, ferulic and sinapic acids. 4-Vinylphenol and 4-vinylguaiacol are volatile phenols associated with off flavors in wine (Eti6vant 1981) and arise from the decarboxylation of p-coumaric and ferulic acid, respectively, via the yeast cinnamate decarboxylase (CD) (Chatonnet et al. 1993). 

A facile synthesis of two naturally occurring 3-deoxyanthocyanidins from 2,4,6-triacetoxybenzaldehyde has been described <03S1878>. A one-step route to pyranoanthocyanins, molecules that have been found in red wine <03TL4887>, involves initial reaction under aqueous conditions of cinnamic acids at the electrophilic 4-position of anthocyanins followed by an intramolecular cyclisation and decarboxylation <03TL7583>. A tri-( )-caffeoyl anthocyanin present in the blue petals of morning glory, Ipomoea tricolor, is resistant to ,Z-isomerisation by UV-B irradiation, a property that may be important in plant survival <03TL7875>. 

As a preparative method the direct decarboxylation of olefinic acids is almost limited to the formation of styrenes and stilbenes from substituted cinnamic acids. Thermal decomposition of cinnamic acid gives styrene (41%). The yield is nearly quantitative if the reaction is carried out in quinoline at 220° in the presence of a copper catalyst. The yields of substituted styrenes where the aryl radical contains halo, methoxyl, aldehyde, cyano, and nitro groups are in the range of 30-76%. cis-Stilbene and cis-p-nitrostilbene are prepared in this way from the corresponding a-phenylcinnamic acids (65%). One aliphatic compound worthy of mention is 2-ethoxypropene, prepared by heating -ethoxycro-tonic acid at 165° (91% yield). The mechanism of acid-catalyzed decarboxylations of this type has been studied. Isomerization of the double bond from the a,/5- to the /5, y-position before decarboxylation very likely occurs in many instances. ... 

Electrolyses of substrates of the cinnamic acid ester family (Table 4) in anhydrous MeCN were shown to result in formation of 7-60% of the CHD [Eq. (3)], corresponding exclusively to the ( ) coupling as determined from the stereochemistry of the cyclopenta-none formed by hydrolytic decarboxylation [61]. The stereochemistry was later verified by x-ray crystallography [65]. The stereoselectivity in the coupling step was originally rationalized in terms of orientation of the substrate molecules at the electrode surface [61]. However, later kinetic studies have shown that dimerization of the radical anions is fairly slow (Table 3), and takes place in the diffusion layer at a distance from the electrode. 

Polymerizations have been carried out under nitrogen in THF or benzene with azobisisobutyronitrile (3% weight) as initiator (Table II). The results are different according to the nature of the cinnamic double bond substituents. Monomers 1 and 2 and corresponding polymers can indeed lose one acid function during polymerizations carried out at reflux temperature. This decarboxylation is in relation with the yield of gel product and molecular weight. Therefore monomers 3 and 4 for which no decarboxylation could occur, have been polymerized without gel formation with high yields. Likewise decarboxylation reaction seems to induce transfert reaction. 

Ethyl phenols are a result of enzymatic activities linked to the decarboxylation of cinnamic acids and the subsequent reduction in vinyl phenols caused by the Brettanomyces/Dekkera yeast genus (Chatonnet et al., 1992), apart from very small quantities produced in peculiar... 

When a /3-hydroxy acid or its /-butyl ester is heated in quinoline solution with a trace of copper powder, decarboxylation and dehydration occur and the product is an exocyclic olefin. For decarboxylation of substituted cinnamic acids in quinoline. 

L-Phenylalanine,which is derived via the shikimic acid pathway,is an important precursor for aromatic aroma components. This amino acid can be transformed into phe-nylpyruvate by transamination and by subsequent decarboxylation to 2-phenylacetyl-CoA in an analogous reaction as discussed for leucine and valine. 2-Phenylacetyl-CoA is converted into esters of a variety of alcohols or reduced to 2-phenylethanol and transformed into 2-phenyl-ethyl esters. The end products of phenylalanine catabolism are fumaric acid and acetoacetate which are further metabolized by the TCA-cycle. Phenylalanine ammonia lyase converts the amino acid into cinnamic acid, the key intermediate of phenylpropanoid metabolism. By a series of enzymes (cinnamate-4-hydroxylase, p-coumarate 3-hydroxylase, catechol O-methyltransferase and ferulate 5-hydroxylase) cinnamic acid is transformed into p-couma-ric-, caffeic-, ferulic-, 5-hydroxyferulic- and sinapic acids,which act as precursors for flavor components and are important intermediates in the biosynthesis of fla-vonoides, lignins, etc. Reduction of cinnamic acids to aldehydes and alcohols by cinnamoyl-CoA NADPH-oxido-reductase and cinnamoyl-alcohol-dehydrogenase form important flavor compounds such as cinnamic aldehyde, cin-namyl alcohol and esters. Further reduction of cinnamyl alcohols lead to propenyl- and allylphenols such as... 

Flavonoids serve as flower pigments, UV protectants, phytoalexins and signal molecules (1,2). Unlike BPS, CHS exhibits a broad substrate specificity (Table I). H. androsaemum CHS and the enzymes from other sources (27) accepted CoA-linked benzoic acids as minor subshates and formed the respective benzophenones. An efficient but unphysiological starter unit is benzoyl-CoA for 2-pyrone synthase (2-PS) that performs only two decarboxylative condensations with malonyl-CoA to produce 6-phenyl-4-hydroxy-2-pyrone (28). In cell cultures of H. androsaemum, benzoic acid originates from cinnamic acid by side-chain degradation (29). The underlying mechanism is CoA-dependent and non-) -oxidative. The complete sequence of enzymes involved was detected. 

Unsaturated Lignin Model Compounds Double bonds in lignin model compounds are attacked by peracetate ions. Dehydro-di-woeugenol (XXI, Figure 12.9) reacted with epoxidation of the aliphatic double bond and formation of the diol. The double bonds in stilbenes [59] and coniferaldehyde [90] are also cleaved. FemUc acid (IVa) and its ethyl ester reacted slowly at 50°C the methyl ether, 3,4-dimethoxy cinnamic acid, was much less reactive and was almost quantitatively recovered [55]. The reactions of ferulic acid and its ethyl ester (both in the trans form) were accompanied by trans-cis isomerization, perhaps an indication of reversible phenoxy radical formation. HomovanilUc acid (XXXa) was also formed the proposed mechanism involved epoxidation of the a-P double bonds followed by decarboxylation. 

Malonic acid undergoes Knoevenagel condensations with nearly every type of aldehyde and with very reactive ketones. If condensations with malonic acid are performed in ethanolic ammonia below 70 C, the methylenemalonic acids are usually obtained. If, however, the condensations are performed in pyridine (Doebner modification), decarboxylation normally takes place and the acrylic or cinnamic acid is... 

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