"Marriage" of Inorganic to Organic Chemistry as Motivation for a Theoretical Study of Chloroform Hydrolysis Mechanisms.

Incorporation of chlorides in coordination complexes, prepared by reactions in CHCl, stimulated MP2 and DFT studies of its complete hydrolysis mechanisms. In excellent agreement with previous experimental results, the most important mechanism for CHCl basic hydrolysis at room temperature is the radical one producing :CCl. The latter inserts into the H-O bond of HO yielding dichloromethanol ().

One-Pot Synthetic Approach to 3-Carboxyl- and 3-Ketopyridines in Aqueous Media.

We describe a one-pot strategy to access 3-carboxyl- and 3-ketopyridines from readily available alkynes and propargylamine a hydroamination process. This one-pot protocol uses alkynes as starting materials, has a broad substrate scope, and operates in aqueous media and open-air conditions. A series of aryl- and alkyl-substituted pyridines were synthesized.

Interesting chemical and physical features of the products of the reactions between trivalent lanthanoids and a tetradentate Schiff base derived from cyclohexane-1,2-diamine.

The initial use of a tetradentate Schiff base (LH) derived from the 2 : 1 condensation between 2-hydroxyacetophenone and cyclohexane-1,2-diamine in 4f-metal chemistry is described. The 1 : 2 reaction of Ln(NO)·HO (Ln = lanthanoid or yttrium) and LH in MeOH/CHCl has provided access to isostructural complexes [Ln(NO)(L'H)(MeOH)] in moderate to good yields. Surprisingly, the products contain the corresponding Schiff base ligand L'H possessing six aliphatic -CH- groups instead of the -CH-(CH)-CH- unit of the cyclohexane ring, an unusual ring-opening of the latter has occurred.

Probing the anomeric effect and mechanism of isomerization of oxazinane rings by DFT methods.

Mechanistic studies of the thermal amine-promoted isomerization of oxazinane rings by DFT methods showed that the isomerization proceeds through abstraction of the C-3 hydrogen atom by the amine nitrogen atom followed by its re-recruitment from C-3 that helps the oxazinane ring to avoid breaking, leading to the same or an isomeric conformer. Calculations also provided evidence that steric effects are responsible for the breaking of the O-N bond in the transition state of the thermal amine-promoted transformations of oxazinane rings, leading to the transformation of the 6-membered ring to a 5-membered ring. Extensive computational studies of the origin of the anomeric effect in the di-substituted oxazinane rings, bearing the EtO substituent at C-6 and CO2Et at C-3, and a series of analogous tetrahydro-2H-pyran ring conformers, revealed that the conformational preferences in both series of compounds are tuned by the balance of non-covalent (weak vDW, dipole-dipole, electrostatic forces, hydrogen bonding) steric effects and hyperconjugative interactions.

Site-selectivity control in hetero-Diels-Alder reactions of methylidene derivatives of lawsone through modification of the reactive carbonyl group: an experimental and theoretical study.

A new perspective on the reactivity of hydroxyquinones was revealed as an acetal derivative of lawsone was synthesized, isolated, and used in tandem Knoevenagel/hetero-Diels-Alder reactions catalyzed by S-proline. The intermediate alkylidene-1,3-diones that were formed in situ reacted with electron rich alkenes to predominantly afford pyrano-1,2-naphthoquinone (β-lapachone) derivatives along with the isomeric pyrano-1,4-naphthoquinone (α-lapachone) derivatives in high to excellent total yields. Interestingly, the highly reactive arylidene-1,3-dione derivatives were found to be stable and isolable.

Cycloaddition Reactions of Indanedioneketene with Electron-Rich Dienophiles: An Experimental and a Theoretical Study.

Thermal decomposition of the phenyliodonium ylide of lawsone gives rise to a highly reactive cyclic α,α'-dioxoketene, indanedioneketene, which reacts with electron-rich dienophiles such as enol ethers to afford [4 + 2] cycloadducts. The initially formed 2,3-dihydro-2-alkoxy-indeno[1,2-b]pyrano-4,5-diones are labile compounds since through an opening of the pyranone ring upon heating they easily tautomerize to alkoxyallylidene-indenedione derivatives and under acid-catalysis they are additionally transformed to 2-(1,3-dihydroxyallylidene)-1H-indene-1,3(2H)-dione or by loss of alcohol to indeno[1,2-b]pyran-4,5-diones. A DFT study explains the polar nature of the cycloaddition reaction, the observed reactivity and suggests a possible mechanism operating in these reactions.

Dimerization of indanedioneketene to spiro-oxetanone: a theoretical study.

Indanedioneketene, a compound resulting from the thermal degradation of the phenyliodonium ylide of lawsone, dimerizes quantitatively to a spiro-oxetanone derivative, a key compound for further transformations. A theoretical electronic structure study of this unusual for alpha-oxoketenes [2 + 2] cyclization reaction both in the gas phase (DFT, MP2) and in dichloromethane solution (DFT), provides support for (a) a single-step, transition-state (involving a four-membered cyclic ring) charge-controlled, concerted mechanism and (b) a [4 + 2] cyclization reaction, not observed but studied theoretically in this study. A parallel study of an open-chain alpha,alpha'-dioxoketene dimerization explains the difference in the stability and reactivity observed experimentally between the cyclic and open-chain products.

Theoretical insights, in the liquid phase, into the antioxidant mechanism-related parameters in the 2-monosubstituted phenols.

The paper describes a DFT/B3LYP study, in the liquid phase, [using the PCM continuum model] on the O-H bond dissociation enthalpy (BDE) and ionization energy (IE) parameter values of the 2-monosubstituted phenols (2-X-ArOH), related to the H-atom transfer (HAT) and single-electron transfer (SET) mechanisms. The solvent and substituent effects on the conformers, the BDEs, and the IEs were studied using four electron-donating (EDG) and five electron-withdrawing (EWG) groups, in seven different solvents. In both the EDG- and/or EWG-substituted species of the parent compounds, radicals, and/or cation radicals, the most stable conformer is varied, depending on the medium and the substitution.

A DFT study on the thermal aryl migration in aryliodonium ylides. Support for a concerted mechanism.

A DFT study on the intramolecular thermal phenyl migration in iodonium ylides supports a concerted mechanism. In contrast to the two, different than each other, suggested mechanisms, involving only intermediates, this study indicates a single-step, transition-state one--involving a five-membered cyclic ring--with no intermediates. The frontier-orbital-controlled migration also confirms the different thermal behavior of two different ylides.

Structure-DPPH* scavenging activity relationships: parallel study of catechol and guaiacol acid derivatives.

The scavenging behavior of a series of catechol and guaiacol acid derivatives toward DPPH(*) was examined having as a starting point the order of activity derived on the basis of theoretically calculated BDE values. The studied compounds were protocatechuic, homoprotocatechuic, dihydrocaffeic, and caffeic acids and also vanillic, homovanillic, dihydroferulic, and ferulic acids. Catechol and guaiacol were used as reference compounds.

PCM study of the solvent and substituent effects on the conformers, intramolecular hydrogen bonds and bond dissociation enthalpies of 2-substituted phenols.

A PCM continuum model, at the DFT/B3LYP level, is used to study the solvent and substituent effects on the conformers, intramolecular hydrogen bond (HB) enthalpies, (Delta H(intra)s), and O-H bond dissociation enthalpies, (BDEs), in 2-substituted phenols, 2-X-ArOH, in the liquid phase. Two electron-donating (edg) and three electron-withdrawing (ewg) substituents are chosen, involved in a variety of biochemical transformations. Seven solvents, differing in their H-bonding ability and polarity, are selected to model different environmental situations.

The gem-Diol Form of (py) CO as a Ligand in Cobalt(II) Carboxylate Clusters: A Cubane Complex and a Novel Nonanuclear Species with a Vertex-Sharing Double Square Pyramidal Structure.

A vertex-sharing double square pyramid of cobalt(II) ions (see picture) is present in the nonanuclear complex 1, obtained by treating cobalt acetate with 0.5 equivalents of (py )CO. The corresponding 1:1 reaction gave 2, which has a central core with a cubane structure.