Decarboxylative method

This microwave-assisted decarboxylation method may have broader applicability as indicated by Aberg et al. who showed two other successful examples of decarboxylations [111]. 

The next task was removal of the C3,C3 -esters. Although the palladium-catalyzed decarboxylation protocol performed well in previous systems, a competing C-H insertion reaction was discovered with the methylidene bridge needed for cercosporin (see below). Since reexamination of alternate decarboxylation methods [48] led to no success, a decarbonylation strategy was explored [49]. Formation of the requisite dialdehyde was best accomplished by overreduction using DIB AL and... 

Non-stabilized a, p y, 5-unsaturated azomethine ylides (158), generated by the decarboxylation method from 3,3-diarylpropenals (156) and secondary amino acids (157), have been found to undergo [1,7]-electrocyclization followed by a [1,5]-hydrogen shift, to yield 2,3-dihydro-17/-2-benzazepines (159). 

Enaminone 128 (Scheme 33) is obtained, together with an isomeric indo-lizine derivative, by flash vacuum thermolysis of aminomethylene Meldrum s acid derivative through intermediate ketene and delocalized azomethine ylide (85TL833). The thermally induced cyclization of semi-cyclic dienamines to afford, for instance, tricyclic 129 is also believed to start with an azomethine ylide (97JOC7744) the p-chlorophenyl substituent is essential for the reaction. Unstabilized ylide 130, on the other hand, is generated from pipecolinic acid and /1-phenylcinnamaldehyde by the decarboxylation method target base 131 is formed by 1,7-electrocycliza-tion and [l,5]-hydrogen shift (99J(P1)2605). 

Substrate Decarboxylation Method Yield (%) Phosphonate Product Yield (%) Ref... 

These are to be considered as maximal values because of elevated blank reading in the range from the NH, peak to the 3-methylhistidine peak (Moore Stein, 1954, M15). For histidine, values obtained by an enzymic specific decarboxylation method are a little lower than those obtained on 150-cm column (Soupart, 1958, S23). 

Dimethyl-4-carbethoxy-2-cyclohexen-l-one and 3,5-di-methyl-2-cyclohexen-l-one have always been prepared from acetaldehyde and acetoacetic ester through the Knoevenagel condensation.2 The keto ester has previously been obtained by selective saponification and decarboxylation methods which have involved heating the crude condensation product with water at 140° 2 3 or with sodium ethoxide in alcohol.3 The ketone has been obtained from the same condensation product by prolonged refluxing in 20% sulfuric acid.2-4 6... 

Decarboxylation methods failed. After several trials, excess phenylmagnesium bromide was used to form the tertiary alcohol, 459, which was treated with acetic anhydride containing a trace of sulfuric acid yielding the tetrasubstituted olefin, 460 (Scheme 56). This olefin was cleaved with ruthenium tetroxide and periodate. The resulting benzophenone was radioactive, thus the pathway to muurolene proceeds via cyclodecadiene as intermediate. 

The free radical chain reaction of 0-acyl thiohydroxamates with a tertiary thiol (r-butyl, triethylmethyl or more recently t-dodecyl) is by far the most wide-ranging reductive decarboxylation method describe to date7 A wide variety of functional groups, including aldehydes, ketones, esters, amides, isolated and conjugated double bonds, are tolerated. Representative examples are given in equations (10) and (11). ... 

The lactones are readily obtained by interaction of oxides and sodio-malonic esters with subsequent hydrolysis and decarboxylation (method 323). The over-all yields are excellent. 

A large number of unsymmetrical ketones have been prepared by the thermal decarboxylation method however, the yields are not recorded. In general, by using a large excess of the short-chain acid (which minimizes formation of the long-chain symmetrical ketone) over thoria at 400°, yields of about 50% are obtained. ° Methyl benzyl ketone and other alkyl aryl ketones have been synthesized in this manner (65%). The use of manganese oxide catalyst at 400° gives about the same results. ... 

The acetoacetic ester synthesis and direct enolate alkylation are two different methods that prepare similar ketones. 2-Butanone, for example, can be synthesized from acetone by direct enolate alkylation with CH3I (Method [1]), or by alkylation of ethyl acetoacetate followed by hydrolysis and decarboxylation (Method [2]). 

The Leffivre-Tollens decarboxylation method for the determination of uronic acids has been applied to soils. This method gives good results with plant material adequately prepared. With soils, however, unbelievably high values for uronic acid, up to 40 % of the soil organic matter, are obtained. The decarboxylation method has been shown to be unsuited for the... 

The decarboxylation method was discussed on page 162 as it is part of the Knoevenagel method of control. The European cockchafer, a root-eating pest, is lured to traps by butyl sorbate (93), a synthetic pheromone. The ester is obviously made from the acid (94) which can be disconnected at the a, bond to give aldehyde (95), again disconnected at thea,/3 bond. 

The self-condensation to give (95) will need no control, and the decarboxylation method is ideally suited to the second step. 

Several reviews have been written which cover the history of the Krapcho reaction through 1982.1,4 Further research in this area revealed the application of the decarboxylation method to compounds such as P-ketoesters, malonate esters, a-cyanoester, and a-sulfonylesters. The classical method for decarboxylation of these compounds usually involves acidic or basic hydrolysis, followed by thermal decarboxylation. Unfortunately, compounds containing acid or base sensitive functional groups are not compatible with these methods. Modem Krapcho conditions have replaced cyanide with less toxic halide anions. Additionally, several decarboxylations have occurred in the absence of salt.4... 

Derivatives based around the use of 2-mercaptopyridine-A-oxide have also featured in decarboxylative methods for the generation of nitrogen-centered radicals. 

Considerable interest has been shown in analytical methods for the determination of algin (68, 72, 78, 101, 158, 171, 21A, 292). Improvements were made in the Lefevre-Tollens hydrochloric acid decarboxylation method by McCready, Swenson, and Maclay (135, 143) to make it more adaptable to routine determinations. Kenyon and coworkers (148, 262, 271, 272) in a series of articles compared various methods for the determination of the carboxyl content of sugar acids. These included the calcium acetate-acetic acid method, the potentiometric titration method in the presence of sodium bromide, decarboxylation and determination of the isolated furfural. Percival and Ross (70, 187) described improvements in the colorimetric carbazole determination of algin. New analytical methods include the oxidation of algin with cerium sulfate (W) and Perlin s (188) recent report of the quantitative thermal decomposition of algin at 255 C. 

Analysis of dietary fiber. Total dietary fiber including both water-soluble and water-insoluble components was analysed with an enzymic method as described by Asp et al. (18). The dietary fiber was characterized by gas-liquid chromatographic assay of monosaccharides after acid-hydrolysis and gravimetric determination of acid insoluble lignin. Uronic acids were assayed with a decarboxylation method. These analyses were performed as described by Theander and Aman (19). 

The radical chain decarboxylation method (see below) has been adapted to a one-carbon homologation procedure for carboxylic acids by trapping the inteimiediate carbon radicals with... 

With the preliminary results in hand, it was crucial that the C2 group on the indole could be readily removed. The C2 carboxylic acid derivatives of coupling products were initially employed toward this endeavor (Scheme 4). There are relatively few decarboxylation methods on indole acids reported in the literature, most of which utilize harsh reaction conditions. Nevertheless, Jagan tested several of the reported methods, including the use of copper chromite in quinoline at 215 °C, copper(I)oxide in DMA at 200 °C, and substoichiometric amounts of indole acid copper salts at 200 Much to his dismay, most of these reactions led to decomposition. Moreover, adjusting temperature or switching to microwave heating failed to provide the desired decarboxylation. 

In heparan sulfate the amount of uronic acid estimated by the carbazole method was much higher than the one found by the decarboxylation method, an observation also made in the case of heparin. Although it has been suggested that this high value was due to the presence of sulfate groups, it is still possible that it depends on the presence of another uronic acid, besides glucuronic acid. 

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