One-flask transformation of secondary amines to nitrones by oxidation with hydrogen peroxide mediated by triscetylpyridinium tetrakis oxodiperoxotungsto-phosphate (PCWP). Some mechanistic considerations

Oxidation of 5-methylaminomethyl uridine (mnm⁵U) by Oxone Leads to Aldonitrone Derivatives

Oxidative RNA damage is linked to cell dysfunction and diseases. The present work focuses on the in vitro oxidation of 5-methylaminomethyl uridine (mnm⁵U), which belongs to the numerous post-transcriptional modifications that are found in tRNA. The reaction of oxone with mnm⁵U in water at pH 7.5 leads to two aldonitrone derivatives. They form by two oxidation steps and one dehydration step. Therefore, the potential oxidation products of mnm⁵U in vivo may not be only aldonitrones, but also hydroxylamine and imine derivatives (which may be chemically more reactive). Irradiation of aldonitrone leads to unstable oxaziridine derivatives that are susceptible to isomerization to amide or to hydrolysis to aldehyde derivative.

An umpolung approach toward N-aryl nitrone construction: a phosphine-mediated addition of 1,2-dicarbonyls to nitroso electrophiles

An umpolung strategy toward the chemoselective construction ofN-aryl nitrones employing a phosphine-mediated addition of 1,2-dicarbonyls to nitroso arenes is described.

Oxidation of primary amines to oximes with molecular oxygen using 1,1-diphenyl-2-picrylhydrazyl and WO3/Al2O3 as catalysts

The oxidative transformation of primary amines to their corresponding oximes proceeds with high efficiency under molecular oxygen diluted with molecular nitrogen (O2/N2 = 7/93 v/v, 5 MPa) in the presence of the catalysts 1,1-diphenyl-2-picrylhydrazyl (DPPH) and tungusten oxide/alumina (WO3/Al2O3). The method is environmentally benign, because the reaction requires only molecular oxygen as the terminal oxidant and gives water as a side product. Various alicyclic amines and aliphatic amines can be converted to their corresponding oximes in excellent yields. It is noteworthy that the oxidative transformation of primary amines proceeds chemoselectively in the presence of other functional groups. The key step of the present oxidation is a fast electron transfer from the primary amine to DPPH followed by proton transfer to give the α-aminoalkyl radical intermediate, which undergoes reaction with molecular oxygen and hydrogen abstraction to give α-aminoalkyl hydroperoxide. Subsequent reaction of the peroxide with WO3/Al2O3 gives oximes. The aerobic oxidation of secondary amines gives the corresponding nitrones. Aerobic oxidative transformation of cyclohexylamines to cyclohexanone oximes is important as a method for industrial production of ε-caprolactam, a raw material for Nylon 6.

Conversion of oximes to carbonyl compounds by triscetylpyridinium tetrakis(oxodiperoxotungsto) phosphate (PCWP)-mediated oxidation with hydrogen peroxide

Aromatic and aliphatic oximes have been deoximated in chloroform-water to the corresponding aldehydes with dilute hydrogen peroxide and triscetylpyridinium tetrakis (oxodiperoxotungsto) phosphate as catalyst. The presence of dipolarophiles in the reaction mixtures allows a competitive reaction that converts oximes into isoxazole and isoxazoline derivatives via the intermediate formation of nitrile oxide species.

Synthesis of 9- and 27-Armed Tetrakis(diperoxotungsto)phosphate-Cored Dendrimers and Their Use as Recoverable and Reusable Catalysts in the Oxidation of Alkenes, Sulfides, and Alcohols with Hydrogen Peroxide

A series of 3- and 9-armed dendrons, functionalized at the focal position to quaternary ammonium salts, were synthesized and characterized. The reaction of these ammonium dendrons with the heteropolyacid H(3)PW(12)O(40) in the presence of hydrogen peroxide led to a family of 9- and 27-armed air-stable polyoxometalate (POM)-cored dendrimers containing a catalytically active trianionic POM species [PO(4)[WO(O(2))(2)](4)](3-) in the core. These POM-cored dendrimers are air-stable, efficient, recoverable, and reusable catalysts for the selective oxidation of alkenes to epoxides, sulfides to sulfones, and alcohols to ketones, in an aqueous/CDCl(3) biphasic system with hydrogen peroxide as the primary oxidant. A study of the countercation effects showed that the dendritic structure increased the stability of the POM species and facilitated the recovery of the catalyst up to the eighth cycle, whereas the increased bulkiness around the POM center led to a negative kinetic dendritic effect. Within the 9-armed POM-cored dendrimer series, the reaction kinetics were susceptible to the nature of the peripheral endgroups. Indeed, the 9-armed n-propyl-terminated POM-cored dendrimer was identified as the most active catalyst. In addition, the results obtained with POM-cored dendrimers versus tetraalkylammonium POMs ([[n-(C(8)H(17))(3)NCH(3)](+)](3)[PO(4)[WO(O(2))(2)](4)](3-) and [[nC(18)H(37)(75 %) + nC(16)H(33)(25 %)](2)N(CH(3))(2)](+)](3)[PO(4)[WO(O(2))(2)](4)](3-)) clearly reveal that the dendritic structures are more stable than their nondendritic counterparts. After the reactions were complete, the dendrimer catalysts were easily recovered and recycled without a discernable lost of activity, whereas attempts to recover tetraalkylammonium POMs gave unsatisfactory results. A significant advantage of the dendritic structures is that they enable the recovery and recyclability of the POM catalyst, in contrast to the other tetraalkylammonium POMs.

Theoretical Study of Reactant Activation in 1,3-Dipolar Cycloadditions of Cyclic Nitrones to Free and Pt-Bound Nitriles

[reaction: see text] 1,3-Dipolar cycloaddition of the cyclic nitrones CH2(CH2)2CH=NO (N1), CH2CH2OCH=NO (N2), CH2-OCH2CH=NO (N3), and O(CH2)2CH=NO (N4) to organonitriles, RCN-both free (R = CH(3), CF(3)) and ligated to Pt(II) and Pt(IV) (in the complexes trans-[PtCl(2)(NCCH(3))(2)] (1) and trans-[PtCl(4)(NCCH(3))(2)] (2))-was investigated extensively by theoretical methods at different levels of theory. The effectiveness of two types of dipolarophile activation (by introducing a strong electron-acceptor group R and by coordination to a metal center) was analyzed and compared. The influence of factors such as the nature of the cyclic nitrone and the nature of the solvent on the reactions was also studied. The reactivity of dipoles and dipolarophiles increases along the series N4 < N1 approximately N3 < N2 and CH(3)CN < CF(3)CN < 1 < 2; the latter demonstrates that the coordination of RCN to a Pt center provides an even higher activation effect upon cycloaddition in comparison with the introduction of a strong electron-acceptor group R such as CF(3). A higher reactivity of the cyclic dipole N1 in comparison with acyclic nitrones (e.g., CH(3)CH=N(CH(3))O) is interpreted to be a result of its exclusive existence in a more strained and hence more reactive E- rather than Z-configuration. The activation and reaction energies have been calculated at different basis sets and levels of theory, up to MP4(SDTQ), CCSD(T), and CBS-Q. The activation energies are weakly sensitive to a change of the correlated methods. The consideration of the solvent effects results in the increase of the activation barriers, and such enhancement is less pronounced for the nonpolar or low polar solvents. The cycloadditions to CH(3)CN and CF(3)CN were found to be nearly synchronous, but these reactions involving 1 and 2 are clearly asynchronous. Moreover, the reaction of N2 with 2 proceeds via a very early acyclic transition state, while for all other reactions the transition states have a cyclic nature.

Asymmetric synthesis of the stereoisomers of 2-amino-5-carboxymethyl-cyclopentane-1-carboxylate

The stereoisomers of 2-amino-5-carboxymethyl-cyclopentane-1-carboxylate may be prepared stereoselectively from diester derivatives of (E,E)-octa-2,6-diendioc acid, with the key step utilising the conjugate addition of homochiral lithium N-benzyl-N- alpha-methylbenzylamide. The trans-C(1)-C(2)-stereoisomers are readily prepared via a diastereoselective tandem conjugate addition cyclisation protocol with lithium (R)-N-benzyl-N- alpha-methylbenzylamide, with subsequent hydrogenolysis and ester hydrolysis giving the (1R,2R,5R)- and (1R,2R,5S)- beta-amino diacids in good yields. The preparation of the cis-C(1)-C(2)-stereoisomers utilises a protocol involving N-oxidation and Cope elimination of the major diastereoisomeric product arising from conjugate addition and cyclisation, giving homochiral (R)-5-carboxymethyl-cyclopentene-1-carboxylate. Conjugate addition of either lithium (R)- or (S)-N-benzyl-N- alpha-methylbenzylamide to (R)-5-carboxymethyl-cyclopentene-1-carboxylate, and diastereoselective protonation with 2,6-di-tert-butyl phenol gives, after hydrogenolysis and ester hydrolysis, the (1S,2R,5R)- and (1R,2S,5R)- beta-amino diacids in good yield. The use of (S)-N-benzyl-N- alpha-methylbenzylamide in the initial conjugate addition and cyclisation reaction, and subsequent repetition of the elimination and conjugate addition strategy allows stereoselective access to all stereoisomers of 2-amino-5-carboxymethyl-cyclopentane-1-carboxylate.

Multiplicity of Reaction Pathways in the Processes of Oxygen Transfer to Secondary Amines by Mo(VI) and W(VI) Peroxo Complexes

Oxidation of N,N-benzylmethylamine, N,N-benzylisopropylamine, and N,N-benzyl-tert-butylamine by both anionic and neutral Mo(VI) and W(VI) oxodiperoxo complexes yields the corresponding nitrones quantitatively. The oxidation reactions employing anionic oxidants were performed in CHCl(3) and follow second-order kinetics, first order with respect to the amine and to the oxidant. The data were rationalized on the basis of a rate-determining nucleophilic attack of the amine onto the peroxide oxygen of the oxidant, with a transition state in which N-O bond formation and O-O bond cleavage occur in a concerted way (electrophilic oxygen transfer mechanism). This attack yields the corresponding hydroxylamine, which then is furtherly oxidized to nitrone in a fast step. On the other hand, in the case of neutral oxidants (1)H-NMR data as well as kinetic data indicate that amine coordinates the metal center replacing the original ligand HMPA and yields a new peroxo complex. For N,N-benzyl-tert-butylamine such a complex was isolated and characterized. These new peroxo complexes can themselves behave as electrophilic oxidants, transferring oxygen to external amine molecules through the same pathway followed by anionic oxidants, or can yield the reaction product by intramolecular oxidation of the coordinate amine. Measurements of added HMPA effects on oxidation rate would seem more consistent with the electrophilic oxygen transfer mechanism.