Decarboxylation-elimination

Reaction No. 5 (Table 11) is part of a synthetically useful method for the alkylation of aromatic compounds. At first the aromatic carboxylic acid is reductively alkylated by way of a Birch reduction in the presence of alkyl halides, this is then followed by an eliminative decarboxylation. In reaction No. 9 decarboxylation occurs probably by oxidation at the nitrogen to the radical cation that undergoes decarboxylation (see... 

The cationic pathway allows the conversion of carboxylic acids into ethers, acetals or amides. From a-aminoacids versatile chiral building blocks are accessible. The eliminative decarboxylation of vicinal diacids or P-silyl carboxylic acids, combined with cycloaddition reactions, allows the efficient construction of cyclobutenes or cyclohexadienes. The induction of cationic rearrangements or fragmentations is a potent way to specifically substituted cyclopentanoids and ring extensions by one-or four carbons. In view of these favorable qualities of Kolbe electrolysis, numerous useful applications of this old reaction can be expected in the future. 

The approach also allows the synthesis of furans by employing ethoxymethylene malonate, followed by an eliminative decarboxylation. This method was used by Balme for a formal synthesis of the antitumor lignan burseran (6/1-294), starting from 6/1-290,6/1-291 and 6/1-292 via the furan 6/1-293 (Scheme 6/1.78) [139], Furans as 6/1-298 can also be obtained by Pd-catalyzed reaction of 2-propynyl-l,3-dicarbonyls 6/1-295 with aryl halides 6/1-296 in DMF, using potassium carbonate as base, as shown by Arcadi, Cacchi and coworkers (Scheme 6/1.79) [140]. 

On heating the condensed [l,2,4]-triazolo[4,3- ]pyridazine-6(577)-one-3(27/)-thione 91 with dialkyl acetylenedi-carboxylates in DMF, the subsequent ring transformations yielded the novel tetracyclic 1,3-diazepine cis-92, which can further be converted to 93 in a number of steps involving elimination, decarboxylation, and cyclization oxidation upon heating (Scheme 15) <2001T7191>. 

On the basis of this palladium-mediated Michael addition cyclization process, a novel two-step synthetic entry into functionalized furan derivatives 67 has also been devised (Scheme 28). Substitution of benzylidene (or alkyli-dene) malonates for their ethoxymethylene analog (65) as activating olefins gave rise to the formation of the corresponding 2-ethoxy-4-arylidene tetrahy-drofurans 66. An in situ addition of potassium ferf-buloxidc induced a decar-boxylative elimination reaction which was followed by an isomerization of the exocyclic double bond. The entire process successively involved a conjugate addition, a palladium-catalyzed cyclization-coupling reaction, a base-induced eliminative decarboxylation, and finally, a double bond isomerization [73]. 

Sodium hydroxide a,j -Acetylenecarboxylic acids by elimination-decarboxylation... 

Pathways of metabolism have been outlined which indicate how tryptophan is a source of auxin, niacin, serotonin, ommochrome, and energy. Many other compounds are formed as side-products of these pathways and still others are formed by further reactions. Yet additional pathways remain to be elucidated to describe the formation of gramine (V-dimethyl-indole-3-methylamine), abrine (A -methyltryptophan), the a-hydroxy-tryptophan component of phalloidin, skatole, and possibly other complex compounds containing the indole nucleus. The reactions involved in these transformations include examples of various types of oxidation, transamination, cleavage, elimination, decarboxylation, and condensation as well as cis-trans isomerization. The wealth of biochemical variety already revealed in these studies is a stimulus toward exploration of the still unknown reactions of tryptophan metabolism. 

It was thought that a new type of analog that does not contain the endocyclic double bond could be synthesized in almost exactly the same manner. Instead of the mono-esterified pimelic acid undergoing the aldol reaction with acrolein, an allyl group could be installed via a simple enolate alkylation reaction. Subsequent methylation, elimination, decarboxylation, cycloaddition, and cross-metathesis steps could be performed in the same manner as before with the result being a more saturated analog (76 Scheme 15). The synthesis to generate diester 73 proceeded as planned however, numerous decarboxylation conditions failed. 

Decarbonylation s. Carbon monoxide, elimination Decarboxylation HGfhC... 

Oxo-4,7-dihydrothieno[2,3- ]pyridine-5-carbonitriles such as compoimd 53 are important intermediates in the synthesis of thieno[2,3-Z)]pyridine-5-carbonitrile kinase inhibitors [130, 131]. A facile three step synthesis of 4-oxo-4,7-dihydrothieno[2,3-i]pyridine-5-carbonitriles 53 from substituted 2-aminothiophene-3-carboxylate esters 7 was developed [132]. The key step of the synthesis is a thermally promoted elimination/decarboxylation followed by nucleophilic cyclization of 52 to give fused thieno-dihydropyridines 53 (Scheme 20) in good yields (Table 10). 

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