Decarboxylative oxidation

Glycol and o -hydroxy acid cleavage Oxidative decarboxylation Oxidative rearrangement of olefins... 

The ring-opening of the cyclopropane nitrosourea 233 with silver trifiate followed by stereospecific [4 + 2] cycloaddition yields 234 [129]. (Scheme 93) Oxovanadium(V) compounds, VO(OR)X2, are revealed to be Lewis acids with one-electron oxidation capability. These properties permit versatile oxidative transformations of carbonyl and organosilicon compounds as exemplified by ring-opening oxygenation of cyclic ketones [130], dehydrogenative aroma-tization of 2-eyclohexen-l-ones [131], allylic oxidation of oc,/ -unsaturated carbonyl compounds [132], decarboxylative oxidation of a-amino acids [133], oxidative desilylation of silyl enol ethers [134], allylic silanes, and benzylic silanes [135]. 

Thiamine diphosphate (TDP) is an essential coenzyme in carbohydrate metabolism. TDP-dependent enzymes catalyze carbon-carbon bond-breaking and -forming reactions such as a-keto acid decarboxylations (oxidative and non-oxidative) and condensations, as well as ketol transfers (trans- and phospho-ketolation). Some of these processes are illustrated in Fig. 12. 

Boiling an ethanolic solution of 4//-pyridazino[6,l-fl]isoquinoline (42) in the presence of KOH for 6 h gave the 4-unsubstituted derivative 53, which was A-acylated with benzoyl chloride (83JOC1084). Heating the A-benzoyl derivative 54 in boiling ethanol in the presence of KOH for 36 h afforded the 2-hydroxy derivative 55, which was also prepared from 56 by basic hydrolysis and subsequent acylation with benzoyl chloride. A decarboxylation-oxidation product 50 was also isolated from the reaction mixture. 

Murahashi and co-workers (49) extensively studied the synthesis of nitrones such as 29 by a decarboxylative oxidation of proline derivatives (Scheme 12.12). However, these nitrones were primarily used in nucleophilic addition reactions rather than 1,3-dipolar cycloadditions. Others have synthesized cyclic nitrones 30 and 31 having a chiral center adjacent to the nitrogen atom (50,51). Saito and co-workers (51) applied nitrone 31 in reactions with fumaric and maleic acid... 

There is some competing decarboxylation of the ethanoic acid, but the conversions in this kind of reaction are usually good. The key steps in the reaction probably are exchange of carboxylic acid groups on tetravalent lead, cleavage of the Pb-O bond to give the carboxylate radical, decarboxylation, oxidation... 

Penicillic acid (Figure 3.45), another micro-bially produced food contaminant with carcinogenic properties, is synthesized by cultures of Penicillium cyclopium and P. baarnense, and also features oxidative ring fission of an aromatic compound. This time orsellinic acid (Figure 3.25) is a precursor, and ring fission appears to proceed via a quinone, which is the result of decarboxylation, oxidation, and methylation reactions. Figure 3.45 also represents an over-simplistic rationalization of the ring fission process. 

Fig. 1. a-Oxidation of amino acids. Hydroxyl radical (or other reactive radical) abstracts hydrogen atom from the a-carbon. The C-centered free radical formed may react with other amino acid residues or dimerize in the absence of oxygen, which leads to protein aggregation. In die presence of oxygen the carbon-centered radical forms peroxyl radical. Reduction of peroxyl radical leads to protein hydroperoxide. Decomposition of hydroperoxide leads to formation of carbonyl compounds via either oxidative deamination or oxidative decarboxylation. Oxidation of the new carbonyl group forms a carboxyl group. 

Oxidative decarboxylation. Oxidation of [n.2.2]propellanecarboxylic acids (1) with lead tetraacetate in pyridine at 80 gives bicyclic acetates 2 and/or tricyclic acetates 3. The latter products are converted into 2 on vapor-phase thermolysis."... 

The conversion of pyruvate into acetyl CoA consists of three steps decarboxylation, oxidation, and transfer of the resultant acetyl group to CoA. 

If the hydroxylic group next to the carboxyl is tertiary, decarboxylative oxidation gives ketones. Benzilic acid is degraded to benzophenone in 85-90% yield on refluxing for 20 min with water and iV-bromosuccinimide [745]. 2-(p-Methoxybenzyl)-p-methoxymandelic acid is converted into des-... 

Lysine is formed in bacteria by decarboxylation of meso-diamino-pimelic acid (Fig. 24-14). Glycine is decarboxylated oxidatively in mitochondria in a sequence requiring lipoic acid and tetrahydrofolate as well as PLP (Fig. 15-20). A methionine decarboxylase has been isolated in pure form from a fem. ° The bacterial dialkylglycine decarboxylase is both a decarboxylase and an aminotransferase which uses pyruvate as its second substrate forming a ketone and L-alanine as products (See Eq. 

Aqueous samples are treated similarly beginning with the acidification step. The entire sample is then put through the hydrophobic resin, and the fulvic acids are eluted at pH 7. The humic acids are removed with 0.1 M NaOH (2). After extraction, purification of the samples can be accomplished by freeze-drying and dialysis. The use of strong acids and bases has been criticized for several reasons. They can promote degradation, decarboxylation, oxidation, and condensation reactions. Strong acids and bases can also dissolve siliceous materials and lyse cells, resulting in contamination of the sample. Other extractants have been proposed, such as sodium pyrophosphate or sodium fluoride however, the classical procedure offers the most complete dissolution of humic material from solid samples and is still most often used (72). 

The structure of the western corn rootworm sex pheromone is 8-methyl-2-decanol propanoate (] 6) and four stereoisomers are possible (Figure 7). In our synthesis (3), we coupled a chiral 5-carbon unit to a 6-carbon fragment that had the requisite substitution to allow resolution at the oxygenated carbon. As mentioned earlier, (S)-2-methylbutyric acid was available to us from the alcohol. D-Isoleucine served as a source for the (R)-acid. Nitrosation, followed by decarboxylative oxidation of the intermediate hydroxyacid led to the (R)-2-methylbutyric acid in 96% ee. The process of fractional crystallization was... 

The synthesis of unsubstituted Dewar benzene was accomplished by van Tamelen (3) 4). Thus, dihydrophthalic anhydride was photochemically isomerized to a [2.2.0]-ring system which was decarboxylated oxidatively to Dewar benzene. This compound has a higher stability than expected from the high strain of its ring system (t1/2 = 37.2 h at 24.3°). This stability was later explained by the rule of the conservation of the orbital symmetry by Woodward and Hoffmann. 

Decarboxylation /-Butylhydroperoxide. Copper powder. Dimethyl sulfoxide. Iron. Decarboxylation, oxidative Lead dioxide. Lead tetraacetate. Pyridine-N-oxide. Degradation, bile acid side chain Periodic acid. 

Isoleucine and valine. The first four reactions in the degradation of isoleucine and valine are identical. Initially, both amino acids undergo transamination reactions to form a-keto-/T methyl valerate and a-ketoiso valerate, respectively. This is followed by the formation of CoA derivatives, and oxidative decarboxylation, oxidation, and dehydration reactions. The product of the isoleucine pathway is then hydrated, dehydrogenated, and cleaved to form acetyl-CoA and propionyl-CoA. In the valine degradative pathway the a-keto acid intermediate is converted into propionyl-CoA after a double bond is hydrated and CoA is removed by hydrolysis. After the formation of an aldehyde by the oxidation of the hydroxyl group, propionyl-CoA is produced as a new thioester is formed during an oxidative decarboxylation. 

Examples. Either or both microwave reactors have been useful for processes such as esterification, amidation, transesterification, rearrangement, acetalization, nucleophilic substitution, hydrolysis of esters and amides, isomerization, decarboxylation, oxidation, elimination, etherification, and formation of aminoreductones. Examples of such reactions have been tabulated (2,3). 

Aza-annulation of 296b with 313, the chloro analog of 311, led to formation of bicyclic pyridone 314 (Scheme 26).89 Modification of this intermediate gave 315, which was then decarboxylated, oxidized, and utilized in the Friedlander quinoline synthesis to give ( )-camptothecin (125). 

Oxidation without decarboxylation. Epstein et al. [4] observed that lAA was destroyed in the endosperm of germinating com kernels at a greater rate than [ ClCOj was evolved from carboxyl labeled lAA, indicating that there must be turnover without decarboxylation. Nonhebel et al. [155] also reported that the rate of decarboxylation was lower than expected when [ C]-IAA was fed to maize seedlings. In maize, the product of non-decarboxylative oxidation of lAA in vivo is oxindole-3-acetic acid (OxIAA Fig. 4)... 

Oxidative decarboxylations. See Decarboxylation Oxidative -elimination. See ( Elimination Oxidative sulfitolysis, 239-240. V-, P- and 5-Oxides deoxygenation, 115 Oximes Beckmann rearr., 136-137 heterocycles from, 307-308 reduction of, 98, 112 Oxirane (ethylene oxide) ... 

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