Decarboxylation Dehydrogenation

The active form of vitamin Be, pyridoxai phosphate, is the most important coenzyme in the amino acid metabolism (see p. 106). Almost all conversion reactions involving amino acids require pyridoxal phosphate, including transaminations, decarboxylations, dehydrogenations, etc. Glycogen phosphory-lase, the enzyme for glycogen degradation, also contains pyridoxal phosphate as a cofactor. Vitamin Be deficiency is rare. 

Decarboxylation-dehydrogenation of allyl -ketocarboxylates (11, 391-392). Pd(OAc)2 is now the preferred catalyst for this reaction.1 An example is a new preparation of 2-methylcyclopentenone (2). 

Table XXXVI is a list of some catalytic photochemical redox transformation of organic reactants by (Q or H)3PW 204o. In the presence of UV light, Q3PW12O40 reacts with paraffins, arenes, alcohols, alkyl halides, ketones, nitriles, thioethers, and water. Under either anaerobic or aerobic conditions, decarboxylation, dehydrogenation, dimerization, polymerization, oxidation, and acylation takes place.

The Cu(II) complex with polyaniline (emeraldine base) exhibits a higher catalytic efficiency for the dehydrogenative oxidation of cinnamyl alcohol into cin-namaldehyde. Iron(III) chloride is similarly used instead of copper(II) chloride. The catalytic system is applicable to the decarboxylative dehydrogenation of man-delic acid to give benzaldehyde. The cooperative catalysis of polyaniline and cop-per(II) chloride operates to form a reversible redox cycle under oxygen atmosphere as shown in Scheme 3.4. The copper salt contributes to not only oxidation process but also metallic doping. The reduced phenylenediamine anionic species appear to be stabilized by the metallic dopants. 

Example 7, Tsuji-Trost decarboxylation-dehydrogenation sequence ... 

Formic acid can decompose in two different ways the decarbonylation-dehydration reaction produces carbon monoxide and water (Equation 3) and the decarboxylation-dehydrogenation process generates hydrogen and carbon dioxide (Equation 4). This latter reaction can be used in hydrogen storage and delivery (having a complete cycle neutral for CO2 emission, with the reverse step). 

Decarboxylation of Carboxylic Acids and Derivatives.—A palladium-catalysed decarboxylation-dehydrogenation of allyl P-keto-carboxylates and allyl enol carbonates occurs in good yield for ten examples however, mixtures of isomers are obtained in some cases (Scheme 32). ... 

Allyl /3-keto carboxylates and allyl enol carbonates undergo a palladium-catalyzed decarboxylation-dehydrogenation to yield o, S-unsaturated ketones in usually high chemical yield and with good selectivity. Following this approach, it was possible to obtain 2-methyl-2-cyclopentenone in two steps from diallyl adipate in a procedure that could be convenient for large-scale preparations (eq 62). ... 

The oxidative decarboxylation of amino acids is performed by VO(OEt)Cl2 [117]. For example, 2-phenylglycine undergoes decarboxylative dehydrogenation, followed by oxidative esterification, to give ethyl benzoate as a major product (Scheme 2.54). 

Two methods of synthesis of the acid (5) from 6-methoxy-l-tetralone (8), formed in two stages from nerolin (7) [139-142], have also been proposed. One of them [143, 144], like that just described above, is based on the introduction of the and 0 2 atoms by the Reformatskii reaction of the ketone (8). The ester formed (10) is converted into the bromide (11) and the 0 3 and 0 4 atoms are introduced by the condensation of the latter with sodiomalonic ester and decarboxylation. Dehydrogenation of the resulting acid (12) gives the acid (5). According to the other method for synthesizing this acid [140], the acids are introduced in one stage... 

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