Radical reactions in malonic acid single crystal between 4 K and 300 K

For three out of the four different radicals which are produced by γ-irradiation in malonic acid single crystals, two stereo-isomers have been observed. The structures and orientations of these radicals were determined. ?H₂COOH proceeds from the cation and is already formed at 4 K; as to H?(COOH)₂, it proceeds from the molecular form of the protonated anion COOHCH₂?(OH)₂.     

Oxidation of methyl phenyl sulfide by carbamide peroxide in the presence of activators

The oxidation of methyl phenyl sulfide by carbamide peroxide in water and water–ethanol mixtures proceeds at the same rates as oxidation by hydrogen peroxide. In the presence of ammonium bicarbonate, the reaction proceeds through a pathway including HCO₄^- as a more active oxidizing agent than H₂O₂.     

Electrochemical formation and reduction of silver oxides in alkaline media

The anodic oxidation of silver electrodes in NaOH solution and the reduction of the silver oxides formed were studied by potential step chronoamperometry. Oxidation of Ag to Ag₂O is a diffusion-controlled reaction, the diffusion control being established in the solid phase. Oxidation of Ag₂O to AgO proceeds via a nucleation and growth-controlled process. The amount of AgO decreased with increasing step height. The current—time curves for this reaction have been analysed with the Kolmogoroff—Avrami equation. Reduction of AgO to Ag₂O occurs initially on the outside of the electrode, and the rate of the reaction is limited by diffusion of ions across the thickening layer of Ag₂O. Reduction of Ag₂O to Ag proceeds via a nucleation and growth reaction.     

Chemische,thermoanalytische und röntgenorgraphische Untersuchungen zur Bildung des β-Ca2[P2O7] aus dem Ca2[P4O12] · 4 H2O

Chemical, Thermoanalytical, and X-ray Investigations to the Formation of the β-Ca₂[P₂O₇] from the Ca₂[P₄O₁₂] · 4 H₂O The formation of β-Ca₂[P₂O₇] from Ca₂[P₄O₁₂] · 4 H₂O (modification I) proceeds crystallographically oriented in several steps: In one of these steps an X-ray amorphous phase is formed and simultaneously cyclotetraphosphate reorganizes to polyphosphate. The dehydration proceeds in 2 steps: At 120°C 3 molecules and at 220°C 1 molecule are lost, respectively. The formation of diphosphate from polyphosphate, which is connected with the loss of P₂O₅, takes place at 850°C according to high temperature Guinier.     

Stereodivergent Synthesis of Arylcyclopropylamines by Sequential CH Borylation and Suzuki–Miyaura Coupling

A step‐economical and stereodivergent synthesis of privileged 2‐arylcyclopropylamines (ACPAs) through a C(sp³)? H borylation and Suzuki–Miyaura coupling sequence has been developed. The iridium‐catalyzed C? H borylation of N‐cyclopropylpivalamide proceeds with cis selectivity. The subsequent B‐cyclopropyl Suzuki–Miyaura coupling catalyzed by [PdCl₂(dppf)]/Ag₂O proceeds with retention of configuration at the carbon center bearing the Bpin group, while epimerization at the nitrogen‐bound carbon atoms of both the starting materials and products is observed under the reaction conditions. This epimerization is, however, suppressed in the presence of O₂. The present new ACPA synthesis results in not only a significant reduction in the steps required for making ACPA derivatives, but also the ability to access either isomer (cis or trans) by simply changing the atmosphere (N₂ or O₂) in the coupling stage.     

Nucleophilic substitution at phosphorus: stereochemistry and mechanisms

This review is devoted to the stereochemistry of nucleophilic substitution reactions at phosphorus. The study of the reactions of phosphoryl group transfer is important for biological and molecular chemistry. The stereochemistry and mechanisms of S_N1(P) monomolecular and S_N2(P) bimolecular nucleophilic substitution reactions of organophosphorus compounds are discussed. It has been shown that hydrolysis of many natural phosphates proceeds according to the monomolecular S_N1(P) mechanism via the formation of metaphosphate intermediate (PO₃^?). S_N2(P) nucleophilic substitution at chiral trivalent or pentavalent phosphorus compounds proceeds via the formation of penta-coordinated transition state or pentacoordinate intermediate.     

Metal‐Free Aminosulfonylation of Aryldiazonium Tetrafluoroborates with DABCO⋅(SO2)2 and Hydrazines

The coupling of aryldiazonium tetrafluoroborates, DABCO?(SO₂)₂, and hydrazines under metal‐free conditions leads to the formation of aryl N‐aminosulfonamides. The reaction proceeds smoothly at room temperature and shows broad functional‐group tolerance. A radical process is proposed for this transformation.     

Stereodivergent Synthesis of Arylcyclopropylamines by Sequential C?H Borylation and Suzuki–Miyaura Coupling

A step‐economical and stereodivergent synthesis of privileged 2‐arylcyclopropylamines (ACPAs) through a C(sp³) H borylation and Suzuki–Miyaura coupling sequence has been developed. The iridium‐catalyzed C H borylation of N‐cyclopropylpivalamide proceeds with cis selectivity. The subsequent B‐cyclopropyl Suzuki–Miyaura coupling catalyzed by [PdCl₂(dppf)]/Ag₂O proceeds with retention of configuration at the carbon center bearing the Bpin group, while epimerization at the nitrogen‐bound carbon atoms of both the starting materials and products is observed under the reaction conditions. This epimerization is, however, suppressed in the presence of O₂. The present new ACPA synthesis results in not only a significant reduction in the steps required for making ACPA derivatives, but also the ability to access either isomer (cis or trans) by simply changing the atmosphere (N₂ or O₂) in the coupling stage.     

Oxidation of aminothiols by molecular oxygen catalyzed by copper ions. Stoichiometry of the reaction

Catalysis of oxidation of aminothiols by copper ions was studied depending on the structure of aminothiols and pH of the medium. The catalytic reaction proceeds in the inner coordination sphere of Cu⁺. At pH 7—9, oxidation of bidentate aminothiols involves reduction of O₂ to H₂O₂. At pH 9—13, oxidation of chelating aminothiols is accompanied by reduction of O₂ to H₂O, whereas oxidation of weak-chelating aminothiols still proceeds by the former mechanism. In this process, the thiolate anions coordinated to the Cu⁺ ions lose one electron each and are oxidized to amino disulfides, which go from the inner sphere of the Cu⁺ complex into a solution. Procedures developed for the determination of amino disulfides, the chemiluminescence determination of H₂O₂ in the presence of aminothiols as luminescence quenchers, and a modified polarographic procedure for the determination of O₂ allowed us to establish that oxidation of aminothiols is not accompanied by catalytic decomposition of H₂O₂ that formed.     

Reaction of [Cp12W2O5] with mercaptocarboxylic acids: Addition rather than reduction. Isolation and characterization of Cp1WO2(SCH2CH2COOH)

The reaction of Cp¹₂W₂O₅ with HS(CH₂)_nCOOH (n = 1, 2) in MeOH or in CH₂Cl₂ solutions at room temperature proceeds in slightly different ways depending on the value of n. For n = 2, it selectively yields compound Cp¹WO₂(SCH₂CH₂CO₂H), which has been isolated and characterized by elemental analysis, NMR and single crystal X-ray diffraction. The reaction is equilibrated, being shifted to the product by absorption of water by anhydrous Na₂SO₄ in CH₂Cl₂, and to the reactants by addition of water. Contrary to the Mo analogue, no products resulting from metal reduction are obtained. The corresponding reaction for n = 1 occurs similarly at low substrate/W ratios (<0.5), but proceeds further to several uncharacterized products for greater substrate amounts. The primary product could not be isolated, but its ¹H NMR spectrum suggests a different, asymmetric structure.     

Catalytic oxidation of thiols to disulfides using iodine and CeCl3·7H2O in graphite

A very simple procedure for the efficient oxidation of thiols to disulfides catalyzed by I₂/CeCl₃·7H₂O in graphite and ethyl acetate as the solvent, in an open system at room temperature is described. The reaction proceeds cleanly under mild conditions and was performed with aromatic, aliphatic, and heterocyclic thiols.     

The Preparation of Potassium Octacyanomolybdate(IV) Dihydrate

K₄Mo(CS)₈ · 2 H₂O was prepared by the reduction of MOO^2? by KBH₄ in potassium cyanide medium. The reduction proceeds during the slow addition of concentrated acetic acid. The synthesis is efficient because reduction and complexation are accomplished at the same time.     

Suzuki reaction on pyridinium N-(5-bromoheteroar-2-yl)aminides

The reactivity of substituted pyridinium N-(2′-azinyl)aminides in Suzuki-Miyaura cross-coupling reaction is reported. The reaction proceeds in good yield employing Cs₂CO₃ as base, and producing substitution on the negatively charged moiety.     

The reaction of eremanthin and isoeremanthin with bromine. Unprecedented simultaneous addition of Br2 to two isolated but topographically related double bonds.

The reaction of $\text{1}$ with Br₂ in CHCl₃ proceeds with the simultaneous and stereospecific incorporation of two moles of Br₂ to give $\text{2}$ thus providing strong experimental evidence for the existence of Br₃.     

Chemo- and diastereoselective cyclopropanation of allylic amines and carbamates

A highly chemo- and diastereoselective protocol for the cyclopropanation of tertiary allylic amines with Shi’s carbenoid [CF₃CO₂ZnCH₂I] is described. The high levels of diastereoselectivity observed in these reactions may be attributed to chelation of the nitrogen atom to the zinc reagent, which then transfers a methylene unit to the syn-face of the olefin. Furthermore, a stereodivergent protocol for the cyclopropanation of a range of allylic carbamates has been developed, which provides access to both diastereoisomers of the corresponding cyclopropanes with very high levels of diastereoselectivity: cyclopropanation with the Wittig-Furukawa reagent [Zn(CH₂I)₂] proceeds under chelation control to give the corresponding syn-product, whilst reaction with Shi’s carbenoid proceeds under steric control to give the corresponding anti-cyclopropane, in >95:5 dr in both cases.     

A novel one-pot conversion of amines to homologated esters in poly(ethylene glycol)

The first deaminative homologation of amines (-CH₂NH₂) to esters (-CH₂CH₂COOEt) in one-pot is reported. The reaction proceeds through, formation of an aldehyde from an amine in the presence of Pd/C as catalyst followed by Wittig reaction and catalytic hydrogenation using poly(ethylene glycol) as the solvent in one-pot.     

Fe-Catalyzed transacetalization of 2-alkoxytetrahydrofurans with alcohols

The transacetalization of 2-alkoxy-4-benzylidenetetrahydrofurans with alcohols proceeds smoothly with the aid of Fe(ClO₄)₃ catalyst. The catalyst reactivity is ordered as Fe(ClO₄)₃ > Zn(ClO₄)₂ > Mg(ClO₄)₂. The present transacetalization provides an entry for various 2-alkoxytetrahydrofurans, which have potential as anticancer agents.     

Reactions of ketenes XVII. Intermediates in the reactions between ketone acetals and ethyl azidoformate

The reaction of the ketene acetals with ethyl azidoformate proceeds via I-ethoxycarbonyl-5,5-dialkoxy-Δ² -1,2,3-triazolines. The latter decomposes easily at room temperature, the reaction pathway depending on the presence of the substituents at the 4-position. Thermolysis and photolysis of the 4-alkyl-substituted triazolines proceed via 1,3-diradicals. The photodecomposition of the 4-unsubstituted triazolines proceeds similarly. The thermal decomposition of the latter is considered either to involve homolytic cleavage of the N₁? N₂ bond to give a 1,5-diradical, or to proceed by a concerted mechanism.     

Non-isothermal Studies on Mechanism And Kinetics of Thermal Decomposition of Cobalt(II) Oxalate Dihydrate

Thermal decomposition of CoC₂O₄⋅2H₂O was studied using DTA, TG, QMS and XRD techniques. It was shown that decomposition generally occurs in two steps: dehydration to anhydrous oxalate and next decomposition to Co and to CoO in two parallel reactions. Two parallel reactions were distinguished using mass spectra data of gaseous products of decomposition. Both reactions run according toAvrami–Erofeev equation. For reaction going to metallic cobalt parameter n=2 and activation energy is 97±14 kJ mol^–1. It was found that decomposition to CoO proceeds in two stages. First stage (0.12<α_II<0.41) proceeds according to n=2, with activation energy 251±15 kJ mol^–1 and second stage (0.45<α_II<0.85) proceeds according to parameter n=1 and activation energy 203±21 kJ mol^–1. This revised version was published online in August 2006 with corrections to the Cover Date.     

A novel reagent combination for the oxidation of highly electron deficient pyridines to N-oxides: trifluoromethanesulfonic anhydride/sodium percarbonate

A novel reagent combination, Tf₂O/Na₂CO₃·1.5H₂O₂, has been developed for the oxidation of highly electron deficient pyridines to their corresponding N-oxides. The N-oxidation reaction, utilizing the in situ generated peracid, proceeds under mild conditions that allow for a number of functional groups and substitution patterns on the pyridine ring.