Oxidative decarboxylations copper acetate

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. 

Interestingly, the Fischer indole synthesis does not easily proceed from acetaldehyde to afford indole. Usually, indole-2-carboxylic acid is prepared from phenylhydrazine with a pyruvate ester followed by hydrolysis. Traditional methods for decarboxylation of indole-2-carboxylic acid to form indole are not environmentally benign. They include pyrolysis or heating with copper-bronze powder, copper(I) chloride, copper chromite, copper acetate or copper(II) oxide, in for example, heat-transfer oils, glycerol, quinoline or 2-benzylpyridine. Decomposition of the product during lengthy thermolysis or purification affects the yields. 

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. 

The oxidative decarboxylation of aliphatic carboxylic acids is best achieved by treatment of the acid with LTA in benzene, in the presence of a catalytic amount of copper(II) acetate. The latter serves to trap the radical intermediate and so bring about elimination, possibly through a six-membered transition state. Primary carboxylic acids lead to terminal alkenes, indicating that carbocations are probably not involved. The reaction has been reviewed. The synthesis of an optically pure derivative of L-vinylglycine from L-aspartic acid (equation 14) is illustrative. The same transformation has also been effected with sodium persulfate and catalytic quantities of silver nitrate and copper(II) sulfate, and with the combination of iodosylbenzene diacetate and copper(II) acetate. ... 

Another widely used decarboxylation procedure involves the use of lead tetraacetate. Depending on the nature of the substrate and the reaction conditions, this reagent may transform a carboxylic acid into an alkane or alkene, or into the respective acetoxy derivative (Scheme 2.144). The most favorable conditions for alkane formation utilize a good hydrogen donor as the solvent. Usually this transformation is carried out as a photochemically induced oxidative decarboxylation in chloroform solution, as is exemplified in the conversion of cyclobutanecarboxylic acid in cyclobutane.In contrast, the predominant formation of alkenes occurs in the presence of co-oxidants such as copper acetate. ... 

Oxidative decarboxylation of cis- and tra .v-2-phenylcyclopropanecarboxylic acid (19) by lead tetraacetate in anhydrous benzene containing copper(II) acetate and pyridine as catalyst affords a mixture of 7 products in a total yield of 55-58% among which phenylcyclopropane (20) and, 2-diphenylcyclopropane (21) were present in only 1.2% and 15% yield, respect-... 

Both trans- and c/j-2-phenylcyclopropanecarboxylic acid (6) can also be decarboxylated with lead tetraacetate in benzene at 80 C in the presence of a catalytic amount of pyridine and copper(II) acetate to give rran. -l,2-diphenylcyclopropane (8) in low yield (18-22%). When the oxidative decarboxylation of these carboxylic acids is carried out with lead tetraacetate in the presenee of iodine under irradiation ra ,v-l-iodo-2-phenylcyclopropane (9) is obtained as the sole product in 43% yield. Under identical conditions 2,2-diphenylcyclopropanecarboxylic acid leads to 2-iodo-l,l-diphenylcyclopropane (mp 45.5 C) in 57% yield. 

Kochi700 found that oxidative decarboxylation by lead tetraacetate is catalyzed not only by pyridine but even more markedly by cupric acetate, Cu(OAc)2, and other copper salts. Since the reaction is inhibited by oxygen, a free-radical reaction apparently is involved. The method is useful in synthesis. Thus Jensen and W. S. Johnson700 converted the tetrahydroabietic acid (1) into the diene mixture (2) in... 

A completely different concept13 makes use of a highly reduced bilane 5 which is oxidatively cyclized to an isobacteriochlorin 6 with copper(II) acetate. The ring closure is initiated by ester cleavage with trifluoroacetic acid and decarboxylative formylation with trimethyl orthoformate to yield a dialdehyde. One of the aldehyde functions forms the desired methine bridge whereas the other is lost during cyclization. 

Benzo[c]thiophene may be prepared by low-pressure (20 mm) vapor-phase catalytic dehydrogenation of l,3-dihydrobenzo[c]thio-phene (Section III,A) at 330° under nitrogen,5,8 by decarboxylation of benzo[c]thiophene-1 -carboxylic acid (Section III,C) with copper in quinoline16,38 or by dehydration of l,3-dihydrobenzo[c]thiophene 2-oxide (Section VI,A) in acetic anhydride or over aluminum oxide at 20 mm Hg and 100°-125° in a sublimation tube.52 A trace of water appears to be beneficial to the first reaction, and it has been suggested53... 

Copper(II) compounds also enhance the rate of decarboxylation of alkanoic acids with lead(IV) acetate by more efficient electron-transfer oxidation of the alkyl radicals produced alkylcopper species may be intermediates 179). 

Dibenzoylsinomenolquinone [in, R = < > -CO] can be oxidized by 30 per cent, hydrogen peroxide in hot glacial acetic acid to 4 5 -dimethoxy-5 6 -di(benzoyloxy)diphenic acid [vn, R = CO], hydrolysis and inethylation of which yields 4 5 5 6 -tetramethoxydiphenic acid [vn, R = Me], and decarboxylation of the latter can be effected by boiling with copper powder in quinoline, giving 2 3 3 4 -tetramethoxy-diphenyl[vm] [15], 4 5 5 6 -Tetramethoxydiphenic acid, like 5 6 5 -trimethoxydiphenic acid [16], could not be resolved into optical isomers [15]. 

Esters 106 (R = Me, Et or Pr = Et, Pr, r-Bu or PhCHi) of aliphatic carboxylic acids react with lithium acetylides 107 (R = H, C5 Hi i or Ph) in the presence of boron trifluoride etherate in THE to give acetylenic ketones 108 (equation 18). Palladium-[tetrakis(triphenylphosphine)]-copper(I) iodide catalyses the oxidative addition-decarboxylation of propargyl methyl carbonates, e.g. 109, with terminal alkynes to yield 1,2-dien-4-ynes (allenylacetylenes) 110. The regiochemistry of the palladium-catalyzed addition of phenylacetylene to the allenic ester 111 depends on the nature of the catalyst used palladium(III) acetate-triphenylphosphine yields a 81 19 mixture of adducts 112 and 113, while in the presence of tetrakis(carbomethoxy)palladacyclopentadiene-tris(2,4,6-trimethoxyphenyl)phosphine the ratio is reversed to 9 91 k... 

In a model synthesis <81CC524>, a nitro-Michael addition of the readily available nitroalkyl pyrrole 36 to mesityl oxide was used to introduce a geminally dimethylated structural element into an AD component rac-39 for the desired chlorin. Reduction of the nitro function in rac-37 leads to the desired AD dimer rac-38 which is combined in the presence hydrobromic acid with the well known a-bromo-a -bromomethyl dipyrromethene 40 after acid induced ester clevage and decarboxylation to yield the tetrapyrrolic biline rac-41. In the final step the linear tetrapyrrole rac-41 undergoes oxidation and cyclization in the presence of copper(II) acetate to give the copper chlorin. The cyclization occurs via the enamine tautomer of rac-41 by nucleophilic attack of the enamine structure on the bromo imine part of the linear tetrapyrrole. 

Alternatively, 3-vinylthiophenes 13 can be prepared through regioselective oxidative coupling of thiophene-2-carboxylic acid derivatives 11 with different alkenes 12 in the presence of a rhodium catalyst ([Cp RhCl2]2) and copper (II) acetate monohydrate as oxidant (Scheme 7) [32]. Thereby, the carboxylic group facilitates ort/io-olefination and is subsequently removed by decarboxylation in a one-pot sequence. Additionally, benzo[Z>]thiophenes can equally be coupled effectively with butyl acrylate giving rise to the vinylated product in a yield of 70%. 

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