Alkenes decarboxylation

The formation of 1-and 2-aIkenes can be understood by the following mechanism. In the presence of formate anion, the 7r-allylpalladium complex 572 is converted into the 7r-allylpalladium formate 573. The most interesting feature is the attack of the hydride from formate to the more substituted side of the (T-allylic system by the cyclic mechanism shown by 574 to form the 1-alkene 575[367]. The decarboxylation and hydride transfer should be a concerted... 

Pyrano[3,4-b]indol-3-ones are the most useful equivalents of the indol-2,3-quinodimethane synthon which are currently available for synthetic application. These compounds can be synthesized readily from indole-3-acetic acids and carboxylic anhydrides[5,6]. On heating with electrophilic alkenes or alkynes, adducts are formed which undergo decarboxylation to 1,2-dihydro-carbazoles or carbazoles, respectively. 

TROST - CHEN Decarboxylation Ni complex catalyzed decarboxylation of dicarboxylic acid anbydndes to form alkenes. 

Carboxylic acids are oxidized by lead tetraacetate. Decarboxylation occurs and the product may be an alkene, alkane or acetate ester, or under modified conditions a halide. A free radical mechanism operates and the product composition depends on the fate of the radical intermediate.267 The reaction is catalyzed by cupric salts, which function by oxidizing the intermediate radical to a carbocation (Step 3b in the mechanism). Cu(II) is more reactive than Pb(OAc)4 in this step. 

Dicarboxylic acids undergo to-decarboxylation on reaction with lead tetraacetate to give alkenes. This reaction has been of occasional use for the synthesis of strained alkenes. 

Reaction of the aldehyde-tethered furanone 244 with pipecolinic acid results in the formation of the oxazolopyr-idine derivative 245, which undergoes spontaneous decarboxylation to give the ylide 246. This in turn undergoes an intramolecular cycloaddition with the tethered exomethylene group to give 247, or with the endocyclic alkene to give the furoindolizine 248 <1997T10633> (Scheme 66). 

Electrophilic substitution of the ring hydrogen atom in 1,3,4-oxadiazoles is uncommon. In contrast, several reactions of electrophiles with C-linked substituents of 1,3,4-oxadiazole have been reported. 2,5-Diaryl-l,3,4-oxadiazoles are bromi-nated and nitrated on aryl substituents. Oxidation of 2,5-ditolyl-l,3,4-oxadiazole afforded the corresponding dialdehydes or dicarboxylic acids. 2-Methyl-5-phenyl-l,3,4-oxadiazole treated with butyllithium and then with isoamyl nitrite yielded the oxime of 5-phenyl-l,3,4-oxadiazol-2-carbaldehyde. 2-Chloromethyl-5-phenyl-l,3,4-oxadiazole under the action of sulfur and methyl iodide followed by amines affords the respective thioamides. 2-Chloromethyl-5-methyl-l,3,4-oxadia-zole and triethyl phosphite gave a product, which underwent a Wittig reation with aromatic aldehydes to form alkenes. Alkyl l,3,4-oxadiazole-2-carboxylates undergo typical reactions with ammonia, amines, and hydrazines to afford amides or hydrazides. It has been shown that 5-amino-l,3,4-oxadiazole-2-carboxylic acids and their esters decarboxylate. 

With respect to the biosynthesis of the solvents it has been speculated on the basis of quantitative data and the identification of (3,y-unsaturated acids in primitive oxytelid beetles that pairs of 1-alkenes and y-lactones are synthesized from corresponding 3-alkenoic acids by either lactonization or by decarboxylation [118]. 

Insertion of aUcynes into aromatic C-H bonds has been achieved by iridium complexes. Shibata and coworkers found that the cationic complex [Ir(COD)2]BF4 catalyzes the hydroarylation of internal alkynes with aryl ketones in the presence of BINAP (24) [111]. The reaction selectively produces ort/to-substituted alkenated-aryl products. Styrene and norbomene were also found to undergo hydroarylation under similar condition. [Cp IrCl2]2 catalyzes aromatization of benzoic acid with two equivalents of internal alkyne to form naphthalene derivatives via decarboxylation in the presence of Ag2C03 as an oxidant (25) [112]. 

Table 9.5. Anodic decarboxylation of vic-diacids to form alkenes in pyridine, water containing triethylamine.

Reaction of 1,2 -dicarboxylic acids has been used for the formation of a number of strained alkenes and also applied to the Diels-Alder addition products from maleic anhydride (Table 9.5). Both cis- and tr s-diacids take part in the process. Aqueous pyridine containing, triethylamine as a strong base, is considered the best solvent and higher yields are obtained at temperatures of around 80 "C [130]. Use of a divided cell avoids a possibility of electrocatalytic hydrogenation of the product at the cathode. The addition of /a/-butylhydroquinone as a radical scavenger prevents polymerization of the product [127], An alternative chemical decarboxylation process is available which uses lead tetraacetate [131] but problems can arise because of reaction between the alkene and lead tetraacetate. 

After extensive screening of various aldehydes to optimize the reaction conditions, it was found that aromatic aldehydes were able to serve as a carbon monoxide source, in which the electronic nature of the aldehydes is responsible for their ability to transfer CO efficiently [24]. Consequently, aldehydes bearing electron-withdrawing substituents are more effective than those bearing electron-donating substituents, with pentafluoro-benzaldehyde providing optimal reactivity. Interestingly, for all substrates tested the reaction is void of any complications from hydroacylation of either the alkene or alkyne of the enyne. Iridium and ruthenium complexes, which are known to decarboxylate aldehydes and catalyze the PK reaction, demonstrated inferior efficiency as compared to... 

Meldrum s acid, like other 1,3-dicarboxyl compounds, was amenable to radical reactions at C-5. The radical reaction between Meldrum s acid benzyl alkyl ethers mediated by InCl3/Cu(OTf)2 has been reported to proceed regioselectively at the benzylic position of the ether moiety (Scheme 35) <2006AGE1949>. Radical reaction of Meldrum s acid and alkenes was carried out with 2equiv of ceric ammonium nitrate (CAN) to give the a-carboxy-lactones which were subsequently subjected to decarboxylative methylenation affording the a-methylene lactones in 35-50% yield (Scheme 35) <2006SL1523>. 

The decarboxylative approach to the ylide formation generated cycloaddition products derived from cycloaddition of the ylide to the carbonyl moiety of the molecule, as opposed to the alkene as seen in previous examples. Kanemasa has reconciled this observation by consideration of the postulated transition state model of the reaction. It was assumed that the steric repulsion of the terminal olehnic substituent and the ylide would favor transition state 309 (Fig. 3.19). Additionally, nonstabilized azomethine ylides have a higher energy HOMO than stabilized ylides, and would therefore prefer the LUMO of the carbonyl than the lower lying alkene LUMO. Formation of fused hve-membered rings would also be kinetically favored over construction of six-membered ring (Scheme 3.103). 

Meier and Heimgartner (208) achieved an intramolecular sydnone-alkene cycloaddition to give adduct 306 in 50% yield. Other tether lengths did not so react, but photolysis of these other sydnones led to novel fused pyrazoles via decarboxylation and subsequent cycloadditions from the subsequent nitrile-imines. 

One of the primary reactions of ionizing radiation with saturated fatty acids is decarboxylation and alkane formation (2). Dimers tend to be produced by reaction of ionizing radiation with unsaturated fatty acids (2). When meats are irradiated C -C 7 n-alkanes, C2-C17 n-alkenes, and C4-Cg iso-alkanes are the predominant products from the lipid fraction (10), Irradiation of the lipoprotein fraction of meat results in the formation of the following volatile compounds Ci-C 7 n-alkanes, C2-C1J n-alkenes, dimethyl sulfide, benzene, and toluene (10). 

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