Decarboxylation cyclization

Mechanistic insight into this process was obtained by administration of labeled trideca- or undeca-3,6,9-trienoic acid instead of the natural C12 precursor (Figure 2). In this case, the artificial 2H metabolites can be analyzed by mass spectrometry without interference from the plants own 1H metabolites, since a homo- or norectocarpene is formed. The sequence of the oxidative decarboxylation/cyclization reaction proceeds without loss of 2H atoms from the double bonds but with loss of a single 2H atom from certain methylene groups of the precursor acids (Figure 3). If C(l) and a 2H atom from C(5) of the labeled precursor is lost, finavarrene is the product of the reaction channel. If the methylene group... 

The use of aliphatic monomers for hyperbranched polyesters has been debated because aliphatic monomers are said to be prone to thermal degradation reactions such as decarboxylation, cyclization, or dehydration [77]. The only commercial hyperbranched polymer is a hydroxy-functional aliphatic polyester, Boltorn, available from Perstorp AB, Sweden. 

The potassium salt of the 3-mercaptopropionic acid derivative 238 undergoes photoinduced decarboxylative cyclization to give the tricyclic product 239 in a low yield after prolonged irradiation (Equation 22)... 

There were relatively few examples reported, in which the chromo-phoric group was an aryl ketone (Ilia) whereas much more PET induced cyclizations with phthalimides (Illb) are known, sometimes other imides, such as succinimides and maleimides were also used. Phthalimides differ from aryl ketones in some respects despite their apparently similar photophysical properties. On one hand, their reduction potential is remarkably lower in comparison with aryl ketones [13]. On the other hand, the radical anion derived from phthalimides is clearly more stable than the corresponding species from aryl ketones [15]. Both facts increase the thermodynamic driving force of a PET and facilitates applications that are unknown from aryl ketones. In this context, one of the most successful approaches is a PET-induced decarboxylation-cyclization route, developed by Griesbeck [13]. The details of this interesting method will be discussed in Sec. 3.4.6. 

Another route to this tetracyclic system involves the decarboxylative cyclization of indolylethyl-tetrahydropyridine derivatives. As an example, heating the diester (120) with aqueous alkali results in hydrolysis, decarboxylation, and cyclization, with the formation (after re-esterification) of one diastereoisomer of the tetracyclic monoester (121).776 However, the stereochemistry of this product has not yet been clarified. 

Doll, M. K. H. A Short Synthesis of the 8-Azaergoline Ring System by Intramolecular Tandem Decarboxylation-Cyclization of the Minisci-... 

During a synthesis of lamellarin and related pyrrole alkaloids, Iwao et al. observed the Pd(OAc)2-mediated decarboxylative cyclization of pyrrole acid 52 to 53 [44]. Lesser amounts (12%) of the product from decarboxylation of 52 were isolated. 

The phthalimide functional group has absorption and ET properties which make it very attractive in terms of PET processes in which it is the oxidizing species. The application of phthalimide derivatives in carbon-carbon bond forming processes with electron-donating groups such as ethers, thioethers, amines, arenes, carboxylates, etc., has been reviewed. A PET decarboxylation-cycliz-ation sequence has been used for the synthesis of medium-sized (8-16) heterocyclic ring systems (15) from AT-phthaloylanthranilic amides coupled to ca-aminoacids (14). The same PET protocol has been used to convert di-, tri-, and tetrapeptides into cyclopeptides with a minimum of protection and activation... 

As mentioned earlier, perchloro-9,10-dihydrophenanthrene gives per-chloro-9,10-phenanthrenequinone. However, under more forcing reaction conditions, perchlorobiphenyl-2,2 -dicarboxylic acid becomes the major product. Longer reaction times afford finally perchlorofluorenone (Ballester et al., 1980c). The sequence (25), involving a decarboxylative cyclization, has been suggested. 

A new method of synthesis of multisubstituted nipecotic acid (piperidine-3-carboxylic acid) derivatives (487) has been developed by way of palladium-catalyzed decarboxylative cyclization of y-methylidene-5-valero-lactones (485) with imines (486) (Scheme 124). ... 

Hyoscyamine is considered to be biosynthesized from a C4 unit derived from two molecules of malonyl CoA attached to the N-methyl-A -pyrrolinium ion, followed by decarboxylation, cyclization, reduction, and esterification [1,2]. The biosynthetic route through which ornithine becomes putrescine by decarboxylation and is transformed to N-methyl-A -pyrrolinium during the biosynthesis of (—)-hyoscyamine was described in the section of the biosynthesis of nicotine. 

Sabitha et al. published an analogous reaction utilizing a D-glucose-derived aldehyde 337 for the construction of the Yonemitsu reaction product 338 (Scheme 13.75) [128]. The aldehyde 340 containing a free hydroxyl group directly led to a decarboxylative cyclization step with the Meldrum s acid moiety, subsequent to the formation of the Yonemitsu product providing 7-(l//-3-indolyl)-2,3-dimethoxy-perhydrofuro[3,2-b]pyran-5-ones 341 in good yields (74-84%). 

A similar reaction procedure with various sugar-derived aldehydes was published by Sapi et al. in 2010 [129]. Deprotection of the oxygen-substituents present in the aldehyde moiety led to the previously discussed decarboxylative cyclization in one additional step providing the desired products in good yields over two steps with high diastereoselectivity. 

In 2012, Kumar et al. reported the Yonemitsu condensa-tion/decarboxylative cyclization sequence in a saccharine-derived ionic liquid at rt, which provides the products in high yields around 90% [130]. The ionic liquid was shown to be recyclable up to four times with only small decrease in the... 

Variation of the Heterocyclic Component Exchanging the indole as the heterocyclic component in the Yonemitsu reaction by imidazo[l,2-fl]pyridines 367 led to a multicomponent synthesis pathway for the preparation of a library of imidazo[l,2-a]pyridin-3-yl carboxylic acids and amides (Scheme 13.80) [138]. Heterocycles bearing a primary amine group tend to decarboxylative cyclization... 

The decarboxylative cyclization could be prevented by using two equivalents of the corresponding aldehyde component 395, which led to spirodihydropyridines 396 as shown by Li et al. (Scheme 13.82) [139], or by exchanging the amino group by a hydroxyl substituent and adding ammonium acetate as the amine source [ 159]. In this 4CR, the Meldrum s acid moiety is hydrolyzed to give the carboxyhc acid 399 that is stabilized by an intramolecular hydrogen bond. 

Shintani, R., Hayashi, S.-Y., Murakami, M., Takeda, M., Hayashi, T. (2009). Stereoselective synthesis of spirooxindoles by palladium-catalyzed decarboxylative cyclization of Y-methylidene-5-valerolactones with isatins. Organic Letters, 11, 3754-3756. 

The decarboxylative cyclization of diphenylacetic acid can be conducted in the presence of [Cp RhCl2]2 [84]/AgSbFg as catalyst system and Cu(0Ac)2-H20 as oxidant, accompanied by decarboxylation to produce fluorene (Scheme 4.81) [85]. 

Although the oxidation potentials of carboxylates are relatively high compared to other electron donor groups (e.g., acetate Eqx. = 1-54 V in MeCN, 2.65 V in HjO vs. SCE), the decarboxylative cyclization proceeds very efficiently and many functional groups are tolerated. As the key step in the reaction, rapid intramolecular photoinduced electron transfer proceeds via the jt,7t state or the higher excited n,Jt triplet state in the nanosecond time regime. ... 

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