Lead oxidative decarboxylation with

The rest of the synthesis (Scheme 13) is completely stereospecific and most of the steps are known (20). The bicyclic acid was oxidatively decarboxylated with lead tetraacetate and copper acetate (21). The resulting enone was alkylated with methyllithium giving a single crystalline allylic tertiary alcohol. This compound was cleaved with osmium tetroxide and sodium periodate. Inverse addition of the Wittig reagent effected methylenation in 85% yield. Finally, the acid was reduced with lithium aluminum hydride to grandisol. 

Stannyl- (and -silyl-) carboxylic acids undergo oxidative decarboxylation with LTA under mild conditions to provide the corresponding alkenes. This represents an improvement on the well-known alkene-forming decarboxylation of acids with LTA, which requires thermtd or photochemical conditions, for example. The directing metal effect leads to improved yields and regioselectivity. However, stereo-specific alkene formation did not occur and this could imply free radical involvement or transmetallation (Pb for Sn) (stereochemistry ) followed by cation formation, see for example Scheme 27. 

As an extension, the same laboratory demonstrated the possibility of performing one-pot oxidative decarboxylations with concomitant iodina-tion when excess iodine was used (Scheme 16) [23]. As illustrated with the pipecolinic carbonate 26, this sequence can be performed followed by trapping of the iminium ion intermediate with 2-hexen-l-ol leading to the functionalized piperidine 27 in 71% yield. Subsequently, a 5-exo cyclization can be performed to give the bicyclic M,0-acetal 28, thus illustrating the potential of preparing complex systems in few steps. 

One synthesis of cyclopentenone [80], requiring a resolution, involved initial ring contraction of phenol when treated with alkaline hypochlorite (49). Resolution of the resulting cis acid [85] was effected with brucine. The desired enantiomer [86] formed the more soluble brucine salt and was thus obtained from the mother liquors of the initial resolution. Oxidative decarboxylation with lead tetracetate, partial dechlorination with chro-mous chloride, and alcohol protection gave chloro enone [87]. Zinc-silver couple (50) dechlorinated [87] to the desired cyclopentenone [80]. 

Further details of Kondo s perillene (236) synthesis (Vol. 5, p. 43 Vol. 6, p. 16) have been publishedanother synthesis was based (Scheme 4) upon photochemical isomerization-lactonization of (237)/ Reduction and alkylation of 3-methyl-2-furoic acid with l-bromo-3-methylbut-2-ene gave (238) which was oxidatively decarboxylated with lead tetra-acetate-cupric acetate to rosefuran (239). ... 

Oxidative decarboxylation. Having occasion to prepare a quantity of 1-carbo-ethoxy-A -bicyclo[2.2.2]-octene (8), Grob and co-workers prepared the anhydride (6) by the neat synthesis formulated and investigated the oxidative decarboxylation with lead dioxide according to Doering (see Lead dioxide). Even with the active lead dioxide of Kuhn and Hammer, the reaction proceeded poorly and the yield of (8) was only 30-37%. The Swiss workers then found that the yield can be more... 

King JA (1947) A new synthesis of /-serine. J Am Chem Soc 69 2738-2741 Kochi JK (1965a) The mechanism of oxidative decarboxylation with lead(IV) acetate. J Am Chem Soc 87 1811-1812... 

One-electron oxidation of carboxylate ions generates acyloxy radicals, which undergo decarboxylation. Such electron-transfer reactions can be effected by strong one-electron oxidants, such as Mn(HI), Ag(II), Ce(IV), and Pb(IV) These metal ions are also capable of oxidizing the radical intermediate, so the products are those expected from carbocations. The oxidative decarboxylation by Pb(IV) in the presence of halide salts leads to alkyl halides. For example, oxidation of pentanoic acid with lead tetraacetate in the presence of lithium chloride gives 1-chlorobutane in 71% yield ... 

The decarboxylation reactions of fluonnated carboxylic acids are similar to those of their nonfluonnated counterparts, but predictably many exceptions exist The oxidation of the potassium salts of perfluoro acids with potassium persulfate leads to decarboxylation and coupling [93] (equation 59)... 

The Cg-amine, originally obtained by the methanolysis of kasugamycin, on treatment with lead tetraacetate or sodium periodate afforded a nitrile amine, with evolution of carbon dioxide, showing a maximum at 2200 cm.-1. This reaction is explained only by the structure (13). The -N-C=N group of the product can be formed by oxidative decarboxylation and can be easily rationalized by the present understanding of such reagents (2, 13) as shown below. On the other hand, the treatment... 

A cursory inspection of key intermediate 8 (see Scheme 1) reveals that it possesses both vicinal and remote stereochemical relationships. To cope with the stereochemical challenge posed by this intermediate and to enhance overall efficiency, a convergent approach featuring the union of optically active intermediates 18 and 19 was adopted. Scheme 5a illustrates the synthesis of intermediate 18. Thus, oxidative cleavage of the trisubstituted olefin of (/ )-citronellic acid benzyl ester (28) with ozone, followed by oxidative workup with Jones reagent, affords a carboxylic acid which can be oxidatively decarboxylated to 29 with lead tetraacetate and copper(n) acetate. Saponification of the benzyl ester in 29 with potassium hydroxide provides an unsaturated carboxylic acid which undergoes smooth conversion to trans iodolactone 30 on treatment with iodine in acetonitrile at -15 °C (89% yield from 29).24 The diastereoselectivity of the thermodynamically controlled iodolacto-nization reaction is approximately 20 1 in favor of the more stable trans iodolactone 30. 

The oxidative decarboxylation reaction above is part of the TCA cycle and leads to the formation of oxaloacetate, which maybe used to synthesize citrate (with acetyl-CoA) or may be used as a substrate by phosphoenol pyruvate carboxykinase, PEPCK. It should be noted that the phosphoenolpyruvate generated by PEPCK reaction shown above is... 

The full paper on the synthesis of onikulactone and mitsugashiwalactone (Vol. 7, p. 24) has been published.Whitesell reports two further useful sequences (cf. Vol. 7, p. 26) from accessible bicyclo[3,3,0]octanes which may lead to iridoids (123 X=H2, Y = H) may be converted into (124) via (123 X = H2, Y = C02Me), the product of ester enolate Claisen rearrangement of the derived allylic alcohol and oxidative decarboxylation/ whereas (123 X = 0, Y = H) readily leads to (125), a known derivative of antirride (126) via an alkylation-dehydration-epoxi-dation-rearrangement sequence. Aucubigenin (121 X = OH, R = H), which is stable at —20°C and readily obtained by enzymic hydrolysis of aucubin (121 X = OH, R = j8-Glu), is converted by mild acid into (127) ° with no dialdehyde detected sodium borohydride reduction of aucubigenin yields the non-naturally occurring isoeucommiol (128 X=H,OH) probably via the aldehyde (128 X = O). ... 

A typical chemical system is the oxidative decarboxylation of malonic acid catalyzed by cerium ions and bromine, the so-called Zhabotinsky reaction this reaction in a given domain leads to the evolution of sustained oscillations and chemical waves. Furthermore, these states have been observed in a number of enzyme systems. The simplest case is the reaction catalyzed by the enzyme peroxidase. The reaction kinetics display either steady states, bistability, or oscillations. A more complex system is the ubiquitous process of glycolysis catalyzed by a sequence of coordinated enzyme reactions. In a given domain the process readily exhibits continuous oscillations of chemical concentrations and fluxes, which can be recorded by spectroscopic and electrometric techniques. The source of the periodicity is the enzyme phosphofructokinase, which catalyzes the phosphorylation of fructose-6-phosphate by ATP, resulting in the formation of fructose-1,6 biphosphate and ADP. The overall activity of the octameric enzyme is described by an allosteric model with fructose-6-phosphate, ATP, and AMP as controlling ligands. 

Brevicolline.—The /3-carboline part of the plant alkaloid brevicolline (114) has been shown to derive from tryptophan (94) and pyruvic acid.37 Putrescine (4) and related compounds provide the pyrrolidine ring.38 A key intermediate in brevicolline biosynthesis is likely to be (113), derived by oxidative decarboxylation of (111), which in turn is formed through the condensation of (94) with pyruvic acid condensation of (113) and (112) (formed from putrescine) would lead to (114). This has been supported by successfully mimicking the biogenetic sequence, starting with the chemical oxidative decarboxylation of (111).39... 

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