Catechols oxidative cleavage

Alcoholysis of cyano acids 9-10 Oxidative cleavage of catechols... 

A problem with the formation of the ternary ES—02 adduct is that it entails an attack of triplet 02 on the singlet substrate, which is a forbidden reaction. However, the presence of iron(III) may provide a mechanism for relaxing this barrier, as suggested by biomimetic studies showing that oxidative cleavage of catechols can be catalyzed by iron(III) centers [145,146], Building on this important early work, Que and coworkers synthesized a series of [Fe(L)(dbc)] complexes where L is a tetradentate tripodal ligand based on trimethylamine with... 

Lin, G., Reid, G., and Bugg, T.D.FI. Extradiol oxidative cleavage of catechols by ferrous and ferric complexes of 1,4,7-triazacyclononane insight into the mechanism of the extradiol catechol dioxygenases, J. Am. Chem. Soc. 123 (2001), 5030-5039. 

The following oxidative cleavage reactions of catechol are typical examples of reactions catalyzed by dioxygenases ... 

Other non-halogenated aromatic compounds are transformed into either catechol or protocatechuate. Then, through a series of oxidative cleavage reactions, catechol and protocatechuate are processed to yield either acetylCoA and succinate, or pyruvate and acetaldehyde. In general, aromatics composed of one, two, or three condensed rings with several types of substitutions are also transformed into catechol. See Figures 9.7a and 9.7b. 

Catechol dioxygenases are nonheme iron enzymes which catalyze the oxidative cleavage of catechols. [Fe(Cat)(Tp )(Hpz )] [Cat = catecholate = C6H4O2, 3,5- Bu2, C6H2O2, C6CI4O2) have been prepared and their reactivity toward O2 investigated.94... 

L-isoleucine, and L-tryptophan was observed, suggesting that 123 likely shares a common biosynthetic pathway with the paraherquamides as shown in Fig. (28). Prenylation of the cyc/o-L-tryptophan-L-13-methylproline and intramolecular [4+2] cyclization (via 126) would provide the putative bicyclo[2,2,2] core (127). Williams and coworkers have already demonstrated that 127 serves as a biosynthetic precursor to paraherquamide A (146) shown in Fig. (33). Oxidation of 127 leads to the catechol derivative (128). Oxidative cleavage of four carbon atoms from the oxygenated aromatic ring in 128 could furnish the spirosuccinimide ring of 123. 

Oxidative cleavage of ring A of the catechol 476 would eventually give the aza-anthraquinone acid 477. Transformation of 477 would lead to 478, in which ring closure to a pyridone 479 would be followed by deoxygenation to form the intermediate sampangine (448). 

Although there has been extensive work done on the oxidative cleavage of catechols catalyzed by copper and other complexes vide infra), less information is available on catalyst complexes that do not carry the reaction beyond the o-quinone stage. 

Catalytic oxidative cleavage of catechols 6.3.1. Base catalyzed oxidations... 

Copper(II) chloride in pyridine with added MeOH activates molecular 0 at room temperature for the oxidative cleavage of catechol to... 

An important question, studied in considerable detail, is whether the oxidative cleavage of catechol and o-benzoquinone does or does not require molecular oxygen. Experiments under anaerobic conditions with the "copper reagent" prepared in the absence of oxygen yielded essentially the same amounts of 21 as the aerobic syntheses. The obvious conclusion is that catechol is stoichiometrically oxidized by a copper(II) species and molcular oxygen is not involved in the cleavage. The function of 0 is merely to reoxidize the copper(I) formed. 

Single-step, 2-electron oxidations were invoked to interpret the mechanism of catechol oxidation to cis,cis-muconic acid monomethyl ester. Catecholatocopper(11) complexes are key intermediates in carbon-carbon bond cleavage in both catechols and o-benzoquinones. The following scheme illustrates the 2-electron steps occurring when the active species is the methoxohydroxocopper(II) dimer (o-benzoquinone is formed as an intermediate) ... 

In base-catalyzed catechol oxidation 0 attacks a catecholato species, producing a peroxo intermediate (or a semiquinone radical anion + 0 ), followed by ring cleavage via a dioxetane. 

The half ester of (E -muconic acid (456) was synthesized in three steps as follows Starting from catechol (457), oxidative cleavage with a peracid led to the (Z,Z)-diacid 458, which was monoprotected via lactonization to provide compound 459, and by treatment with Eschenmoser s base the desired monoester 460 was obtained (Scheme 8.15). 

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