Castro reaction oxidation

Although much of the biological literature focuses on nitrosating reactions of nitric oxide, chemically nitric oxide is a moderate one-electron oxidant, making formation of nitroxyl anion feasible under physiological conditions. The reduction potential to reduce nitric oxide to nitroxyl anion is +0.39 V, whereas it requires +1.2 V to oxidize nitric oxide to nitrosonium ion. Nitrosating reactions of nitric oxide are often mediated by conversion of nitric oxide to another nitrogen oxide species or by direct reaction with transition metals (Wade and Castro, 1990). 

The spontaneous reaction of nitric oxide with thiols is slow at physiological pH and the final product under anaerobic conditions is not a nitrosothiol (Pryor et al., 1982). The reaction is slow because it involves the conjugate base of the thiol (R—S"). At pH 7.0, the oxidation of cysteine by nitric oxide required 6 hr to reach completion and yields RSSR and N 2O as the products. The synthetic preparation of nitrosothiols usually involves the addition of nitrosonium ion from acidified nitrite to the thiol, or oxidation of the thiol with nitrogen dioxide under anaerobic conditions in organic solvents. Nitric oxide will form nitrosothiols by reaction with ferric heme groups, such as found in metmyoglobin or methemoglobin (Wade and Castro, 1990). It is also possible that nitrosyldioxyl radical also reacts with thiols to form a nitrosothiol. 

Boc-L-Leucinal 1s a useful chiral synthon in the preparation of the natural amino acid statine [S-(R, R )]-4-am1no-3-hydroxy-6-methylheptanoic acid (3S.4S). The procedure reported here Is based on the method of Fehrentz and Castro for the preparation of optically active Boc amino aldehydes from a-amino acids. It Is satisfactory on a kilogram scale. Boc-L-Leucinal has also been prepared by the reduction of Boc-L-leucine methyl ester with d1Isobutyl aluminum hydride or by oxidation of Boc-L-leucinolThe reaction conditions described here differ from those In the literature. The N-... 

The majority of reported reactions of aryl and heteroaryl substrates with organocopper reagents are examples of Stephens-Castro coupling or the more recent catalytic version of that reaction. The reaction has found recent application in syntheses of C-(6)-substituted pterins and pteridines, substituted pyridines, and the antitumor antibiotic fredericamycin A," to name a few. Aryl iodide can be che-mospecifically displaced in the presence of bromide," and 2,5-dibromopyridine is regioselectively substituted at the 2-position. Substitution of halobenzenes by propargyl alcohol, followed by oxidative cleavage, provides a convenient route to terminal arylalkynes. " Fused heterocycles are formed in reactions of aryl halides bearing nucleophilic ortho substituents. - "... 

Ethynylcopper compounds, isolated or generated in situ, play a fundamental role in acetylene synthesis. The reactions basically are of three types the Glaser and Cadiot-Chodkiewicz oxidative couplings employed in polyacetylene synthesis, and the Castro coupling for preparing arylacetylenes (for comprehensive reviews of these reactions see ref. 9). 

Whilst acetylenic alcohols can be employed directly in Cadiot-Chodkiewicz reactions [9], protection of the alcohol (usefully as the Thp ether) is necessary for Castro coupling [14]. A variation based upon these two processes involves coupling of terminal alkynes with 3-bromopropynol (10) in the presence of pyridine [15]. For primary alcohol products, oxidation to the aldehyde with nickel peroxide followed by base-catalyzed decarbonylation generates the new terminal acetylene e.g. Fig. 1.10. 

The production of toluene 1,2-epoxide (C) and 2-methy oxepin (D) by the pathway (b) was proposed by Klotz et al. (2000). Their reaction rates with OH was found to be fast experimentally and theoretically, and they are thought to be one of the formation pathways to the open-ring compounds described below (Cartas-Rosado and Castro 2007). In the case of benzene, it has been reported that phenol is formed from the photolysis of benzene oxide and oxepin (Klotz et al. 1997), but the cresols are not formed from toluene 1.2-epoxide or 2-methyl oxepin (Klotz et al. 2000). 

Machado, G.S., Castro, K, Wypych, F. Nakagaki, S. (2008) Immobilization of metalloporphyrins into nanotubes of natural halloysite toward selective catalysts for oxidation reactions. Journal of Molecular Catalysis a-Chemical, 283, 99-107. 

A possible mechanism for the conversion of aryl halides 38 to aryl nitriles 40 invokes a copper(III) intermediate 41, which is reminiscent of the postulated key complex 35 in the Cadiot-Chodkiewicz mechanism outlined above. Despite the gross similarities among these three transformations, there is no clear evidence that the oxidative addition/elimination pathway and copper(III) intermediates which define the Cadiot-Chodkiewicz and Rosenmund-von Braun reaction mechanisms are operant in the typical Castro-Stephens coupling. 

Julien C, Castro-Garcia S (2001) Lithiated cobaltates for Li-ion batteries. Structure, morphology and electrochemistry of oxides grown by solid-state reaction, wet chemistry and flhn deposition. J Power Sourc 97-98 290-293... 

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