Decarboxylative catalytic transformations

Sun, Z.-M., Zhao, P. (2009). Rhodium-mediated decarboxylative conjugate addition of fluorinated benzoic acids stoichiometric and catalytic transformations. Angewandte Chemie International Edition, 48, 6726-6730. 

Since 2006, the efficiency of decarboxylative couplings has steadily been improved, and they are on the way to becoming standard tools for organic synthesis [1-4]. A growing number of researchers have developed a wealth of catalytic transformations starting from carboxylic acids with release of CO2, providing... 

The utilization of the Robinson annellation method for the synthesis of cory-nanthe-type alkaloids has been thoroughly investigated by Kametani and coworkers (149-152). The tetracyclic ring system was efficiently formed via the Michael addition of dimethyl 3-methoxyallylidenemalonate (247) to the enamine derived from 3,4-dihydro-1 -methyl-(3-carboline (150). Alkylation of 248, followed by hydrolysis and decarboxylation, resulted in a mixture of stereosiomeric enamides 250 and 251. Hydrogenation of 250 afforded two lactams in a ratio of 2 1 in favor of the pseudo stereoisomer 253 over the normal isomer 252. On the other hand, catalytic reduction of 251 gave 254 as the sole product in nearly quantitative yield. Deprotection of 254, followed by lithium aluminum hydride reduction, yielded ( )-corynantheidol (255) with alio relative configuration of stereo centers at C-3, C-15 and C-20. Similar transformations of 252 and 253 lead to ( )-dihydrocorynantheol and ( )-hirsutinol (238), respectively, from which the latter is identical with ( )-3-epidihydrocorynantheol (149-151.). 

Furthermore, the first catalytic synthesis of allenes with high enantiomeric purity [15c, 25] was applied recently to the pheromone 12 by Ogasawara and Hayashi [26] (Scheme 18.7). Their palladium-catalyzed SN2 -substitution process of the bromo-diene 16 with dimethyl malonate in the presence of cesium tert-butanolate and catalytic amounts of the chiral ligand (R)-Segphos furnished allene 17 with 77% ee. Subsequent transformation into the desired target molecule 12 via decarboxylation and selenoxide elimination proceeded without appreciable loss of stereochemical purity and again (cf. Scheme 18.5) led to the formation of the allenic pheromone in practically the same enantiomeric ratio as in the natural sample. 

This section concerns catalytic processes that transform chemicals from renewables by C-C bond breaking. Among these are thermochemical processes, such as pyrolysis and also gasification, catalytic reactions, such as catalytic cracking and different reforming reactions, and decarbonylation and decarboxylation reactions. Many of these reactions occur simultaneously, particularly in the thermochemical processes. Another technically important class of C-C bond breaking reactions is the fermentation processes, however, they will not be considered in this section since they do not involve heterogeneous catalysis. 

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 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. ... 

Studies on thiamine (vitamin Bi) catalyzed formation of acyloins from aliphatic aldehydes and on thiamine or thiamine diphosphate catalyzed decarboxylation of pyruvate have established the mechanism for the catalytic activity of 1,3-thiazolium salts in carbonyl condensation reactions. In the presence of bases, quaternary thiazolium salts are transformed into the ylide structure (2), the ylide being able to exert a cat ytic effect resembling that of the cyanide ion in the benzoin condensation (Scheme 2). Like cyanide, the zwitterion (2), formed by the reaction of thiazolium salts with base, is nucleophilic and reacts at the carbonyl group of aldehy s. The resultant intermediate can undergo base-catalyzed proton... 

Several co-oxo fatty acids are transformed to the corresponding a,co -dicarboxylic acids, whereas -formylesters of fatty acids are decarboxylated to the co-hydroxy fatty acids and carbon dioxide1111. For several co-oxo fatty acids turnover frequencies (measured as O2 consumption) between 1.8 to 25 s 1 were found. Many P450 systems are multi-component enzymes with small protein cofactors such as putidaredoxin performing the electron mediation between NAD(P)H and the active site of the enzyme. Vilker and coworkers recently were able to show that NADPH can be omitted from the catalytic cycle by direct electrochemical reduction of putidar-... 

Alkylquinoxalines have also been prepared by various transformations of preformed quinoxalines. Thus 2-carboxy groups are usually readily decarboxylated and 2-chloro groups removed by catalytic hydrogenation. Illustrative of this approach is the reduction of 2-chloro-3-methylquinoxaline to 2-methylquinoxaline. " ... 

This review covers the catalytic literature on condensation reactions to form ketones, by various routes. The focus is on newer developments from the past 15 years, although some older references are included to put the new work in context. Decarboxylative condensations of carboxylic acids and aldehydes, multistep aldol transformations, and condensations based on other functional groups such as boronic acids are considered. The composition of successful catalysts and the important process considerations are discussed. The treatment excludes enantioselective aldehyde and ketone additions requiring stoichiometric amounts of enol silyl ethers (Mukaiyama reaction) or other silyl enolates, and aldol condensations catalyzed by enzymes (aldolases) or catalytic antibodies with aldolase activity. It also excludes condensations catalyzed at ambient conditions or below by aqueous base. Recent reviews on these topics are those of Machajewski and Wong, Shibasaki and Sasai, and Lawrence. " The enzymatic condensations produce mainly polyhydroxyketones. The Mukaiyama and similar reactions require a Lewis acid or Lewis base as catalyst, and the protecting silyl ether or other group must be subsequently removed. However, in some recent work the silane concentrations have been reduced to catalytic amounts (or even zero) this work is discussed. 

Diels-Alder reaction of pyran-2-ones. Diels-Alder reaction of 2-pyrones, if successful, can provide unusual cyclohexenecarboxylic acids, but thermally promoted cycloadditions with these electron-deficient dienes usually result in decarboxylation and aromatization of the adducts as a result of the required high temperatures (6,291-292). Successful Diels-Alder reactions of 3-bromo-2-pyrone (1) with the electron-rich dioxole 2 can be effected with a catalytic amount of ethyldiisopropylamine at 90° (4 days) to give the major adduct (endo-3) in 63% yield. The adduct is hydrolyzed by p-toluenesulfonic acid in methanol to 4 as the only diastereomer. The trisilyl ether of 4 was transformed to the a,/8-unsaturated ester 5 by radical debromination and DBU isomerization. ... 

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