Orbital analysis of bonding in diarylhalonium salts and relevance to periodic trends in structure and reactivity.

Diarylhalonium compounds provide new opportunities as reagents and catalysts in the field of organic synthesis. The three center, four electron (3c-4e) bond is a center piece of their reactivity, but structural variation among the diarylhaloniums, and in comparison with other λ-iodanes, indicates that the model needs refinement for broader applicability. We use a combination of Density Functional Theory (DFT), Natural Bond Orbital (NBO) Theory, and X-ray structure data to correlate bonding and structure for a λ-iodane and a series of diarylchloronium, bromonium, and iodonium salts, and their isoelectronic diarylchalcogen counterparts.

Regioselective Synthesis of 1,2,3,4-Tetrasubstituted Arenes by Vicinal Functionalization of Arynes Derived from Aryl(Mes)iodonium Salts*.

Herein, the synthesis of 1,2,3,4-tetrasubstituted benzenoid rings, motifs found in pharmaceutical, agrochemical, and natural products, is described. In the past, the regioselective syntheses of such compounds have been a significant challenge. This work reports a method using substituted arynes derived from aryl(Mes)iodonium salts to access a range of densely functionalized 1,2,3,4-tetrasubstituted benzenoid rings.

Crystal Structures of DOTMA Chelates from Ce to Yb : Evidence for a Continuum of Metal Ion Hydration States.

The crystal structures of chelates formed between each stable paramagnetic lanthanide ion and the octadentate polyamino carboxylate ligand DOTMA are described. A total of 23 individual chelates structures were obtained; in each chelate the coordination geometry around the metal ion is best described as a twisted square antiprism (torsion angle -25.0°--31.

Design, Synthesis, and Preliminary Studies of Spiro-isoxazoline-peroxides against Human Cytomegalovirus and Glioblastoma ∥.

The association between glioblastoma (GBM) and human cytomegalovirus (HCMV) infection has been the intensely debated topic over the decades for developing new therapeutic options. In this regard, the peroxides from natural and synthetic sources served as potential antiviral and anticancer agents in the past. Herein, a concise and efficient strategy has been demonstrated to access a novel class of peroxides containing a spiro-isoxazoline to primarily investigate the biological activities.

Electrocatalytic reduction of CO with CCC-NHC pincer nickel complexes.

A CCC-NHC pincer Ni(ii)Cl complex was prepared according to the metallation/transmetallation methodology. It was fully characterized by electrochemical, NMR spectroscopic, theoretical, and X-ray crystallographic methods. The complex and its cation were evaluated for electrocatalytic reduction of CO under a variety of conditions and found to provide some of the fastest catalytic rates and highest substrate selectivities (COvs.

Hexacoordinate Ru-based olefin metathesis catalysts with pH-responsive N-heterocyclic carbene (NHC) and N-donor ligands for ROMP reactions in non-aqueous, aqueous and emulsion conditions.

Three new ruthenium alkylidene complexes (PCy3)Cl2(H2ITap)Ru=CHSPh (9), (DMAP)2Cl2(H2ITap)Ru=CHPh (11) and (DMAP)2Cl2(H2ITap)Ru=CHSPh (12) have been synthesized bearing the pH-responsive H2ITap ligand (H2ITap = 1,3-bis(2',6'-dimethyl-4'-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene). Catalysts 11 and 12 are additionally ligated by two pH-responsive DMAP ligands. The crystal structure was solved for complex 12 by X-ray diffraction.

Synthesis and Investigation of Novel Spiro-isoxazolines as Anti-Cancer Agents.

A series of structurally diverse 4-bromo spiro-isoxazolines possessing a variety of aromatic and aliphatic substituents at the 3 position, were synthesized through a 1,3-dipolar cycloaddition followed by intramolecular cyclization of a pendant hydroxyl or carboxylic acid group. The biochemical antiproliferative activity was evaluated by using two breast cancer cell lines (MCF-7 and MDA-MB-231) and two prostate cancer cell lines (PC-3 and DU-145) using the MTT viability assay, and the IC values were obtained. Spiro-isoxazoline derivatives bearing a -chloro or an -dichloro aromatic substituent at the 3-position of the isoxazoline showed considerable antitumor activities in all four cell lines with IC value ranging from 43μM to 56μM.

A Model Study toward the Concise Synthesis of Bromotyrosine Derived Spiroisoxazoline Natural Products and Analogous Core Structures.

A model study of the first non-aromatic ring based approach toward α-hydroxyspiroisoxazolines resembling the bromotyrosine derived natural product and analogous spiroisoxazoline core structures were implemented. The desired molecular architecture was achieved through the multifunctionalization of a key 1,3-diketo spiroisoxazoline. Our strategy could serve as an efficient alternative of previously developed approaches that utilize an aromatic ring oxidation as the essential step to synthesize this class of natural products.

Synthesis and Tautomerism of Spiro-Pyrazolines.

An experimental study on the synthesis, tautomerism and acid promoted structural changes of spiro-pyrazolines is described. The target was achieved through a [3+2]-dipolar cycloaddition of an alkene with nitrile imines generated and was isolated in high yield. The synthesized cycloadduct displayed a tendency to exhibit an imine-enamine type of tautomerism as evidenced by X-ray crystal and NMR studies.

Picture of a chelate in exchange: the crystal structure of NaHoDOTMA, a 'semi'-hydrated chelate.

Crystallography generally only provides static structural information. This can render it an ineffective technique for probing dynamic solution state processes. A crystal of HoDOTMA affords unique structures that effectively represent that of a lanthanide tetra-acetate chelate mid-way through the water exchange process.

Toward molecular rotors: tetra-N-heterocyclic carbene Ag(I)-halide cubane-type clusters.

1,3-Bis(3'-butylimidazol-1'-yl)benzene diiodide (2a), 1,3-bis(3'-but-3''-enyl-imidazolium-3'-yl)benzene diiodide (2b), 1,3-bis(3'-pent-4''-enyl-imidazolium-3'-yl)benzene diiodide (2c), 1,3-bis(4'-butyl-1',2',4'-triazolium-1'-yl)benzene diiodide (2d), or 1,3-bis(4'-butyl-1',2',4'-triazolium-1'-yl)benzene dibromide (2e) was reacted with Ag2O yielding unprecedented tetra-N-heterocyclic carbene-Ag(I)-X cubane-type clusters. These were characterized by (1)H and (13)C NMR spectroscopy, ESI-TOF MS, elemental analysis, and X-ray crystallography. Results from VT (13)C NMR spectroscopy and cross-over experiments are consistent with intramolecular exchange suggesting that the Ag(I) complexes are molecular rotors.

Synthesis of Novel Pyrazoles via [2+3]-Dipolar Cycloaddition Using Alkyne Surrogates.

The syntheses of an important class of hitherto unreported novel pyrazoles are described. The regioselective synthesis of 1,3,4,5-tetrasubstituted pyrazoles was achieved by the Huisgen cyclization of nitrile imines with a trisubstituted bromoalkene. The substituted bromoalkene functions as an alkyne synthon which was used to construct 5,5-disubstituted bromopyrazoline intermediates that undergo aromatization to the analogous pyrazoles through the loss of HBr.

Construction of Novel Spiroisoxazolines via Intramolecular Cyclization/Methylation.

Improved yields for the syntheses of a variety of spiroisoxazolines were achieved through intramolecular cyclization/methylation reactions of functionalized 5,5-disubstituted isoxazolines in one reaction vessel. Aromatic ring containing nitrile oxides and disubstituted geminal alkenes reacted in a 1,3-dipolar fashion to afford the corresponding 5,5-isoxazoline. A comparison of the relative location of the nucleophile and electrophile on the isoxazoline and two different ester functional groups was performed in order to determine the best isoxazoline system for the intramolecular cyclization/methylation reaction.

Oxonium Ion Mediated Synthesis of 4-Substituted Spiro-Isoxazolines.

The stereoselective synthesis of 4-bromo-spiro-isoxazolines was achieved in one step through the bromination of various isoxazoles that contain a pendant alcohol or carboxylic acid functional group. Isoxazole bromination leads to a bromonium ion intermediate which opens either by neighboring oxygen lone pair electrons or by intramolecular nucleophilic attack. Single X-ray crystal data provides evidence that the two contiguous stereocenters of the spiro-isoxazoline are formed by the anti intramolecular attack of the nucleophile relative to bromine since there is an anti stereochemical relationship between the spirocyclic ring oxygen and the bromine atom.

A Novel Synthesis of 1,3,5-Trisubstituted Pyrazoles through a Spiro-pyrazoline Intermediate via a Tandem 1,3-Dipolar Cycloaddition/Elimination.

The syntheses of an important class of hitherto unreported 1,3,5-pyrazoles, inspired by an unanticipated eliminatory ring opening are described. The reported pyrazole compounds were constructed through the Huisgen cyclization of 2-methylene-1,3,3-trimethylindoline and an in situ generated nitrile imine. The newly formed spiro-pyrazoline intermediate presumably then undergoes a ring opening/elimination process to afford a pyrazole, as evidenced by single X-ray crystal data.

Improved molecular weight control in ring-opening metathesis polymerization (ROMP) reactions with ru-based olefin metathesis catalysts using N donors and acid: a kinetic and mechanistic investigation.

The effect of the addition of H(3)PO(4) on the ROMP activity of cyclooctene (COE) with first- [Cl(2)(PCy(3))(2)Ru=CHPh] and second-generation [(H(2)IMes)Cl(2)(PCy(3))Ru=CHPh] Grubbs' catalysts 1 and 4 (Cy=cyclohexyl, Ph=phenyl, Mes=2,4,6-trimethylphenyl (mesityl)), their inhibited mixtures with 1-methylimidazole (MIM), as well as their isolated bis-N,N'-dimethylaminopyridine (DMAP) derivatives [Cl(2)(PCy(3))(DMAP)(2)Ru=CHPh)] (5 b) and [Cl(2)(H(2)IMes)(DMAP)(2)Ru=CHPh] (7 b) (DMAP=dimethylaminopyridine), a novel catalyst, has been investigated. The studies include the determination of their initiation rates, as well as a determination of the molecular weights and molecular weight distributions of the polymers obtained with these catalysts and catalyst mixtures from the exo-7-oxanorbornene derivative 11. The structure of catalyst 7 b was confirmed by means of X-ray diffraction.

Olefin metathesis catalysts bearing a pH-responsive NHC ligand: a feasible approach to catalyst separation from RCM products.

Two novel ruthenium-based olefin metathesis catalysts, H(2)ITap(PCy(3))Cl(2)Ru[double bond, length as m-dash]CH-Ph and H(2)ITapCl(2)Ru[double bond, length as m-dash]CH-(C(6)H(4)-O-iPr) (H(2)ITap = 1,3-bis(2',6'-dimethyl-4'-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene), were synthesized bearing a pH-responsive NHC ligand with two aromatic NMe(2) groups. The crystal structures of complexes and were determined via X-ray crystallography. Both catalysts perform ring opening metathesis polymerization (ROMP) of cyclooctene (COE) at faster rates than their commercially available counterparts H(2)IMes(PCy(3))Cl(2)Ru[double bond, length as m-dash]CH-Ph and H(2)IMesCl(2)Ru[double bond, length as m-dash]CH-(C(6)H(4)-O-iPr) (H(2)IMes = 1,3-bis(2',4',6'-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) and perform at similar rates during ring closing metathesis (RCM) of diethyldiallylmalonate (DEDAM).

An improved method for the synthesis of zirconium (CCC-N-heterocyclic carbene) pincer complexes and applications in hydroamination.

Upon heating Zr(NMe(2))(4), 1,3-bis(N-butyl-imidazolium)benzene diiodide and toluene analytically pure Zr pincer complex was obtained, which was found to be an intramolecular hydroamination catalyst.

Cyclotridecanone 2,4-dinitrophenylhydrazone.

In cyclotridecanone 2,4-dinitrophenylhydrazone, C(19)H(28)N(4)O(4), the 13-membered carbocycle exists in the triangular [337] conformation. The 2,4-dinitrophenylhydrazone group is almost perpendicular to the 13-membered ring, with a dihedral angle of 82.66 (2) degrees between the mean planes.

Regio- and stereoselective glycosylation: synthesis of 5-haloimidazole alpha-ribonucleosides.

We describe the synthesis of novel 5-haloimidazole ribonucleosides as precursors of modified cobalamins. A regio- and stereoselective glycosylation of protected ribose with silylated 4(5)-haloimidazoles produces 5-haloimidazole ribonucleosides predominantly in the alpha-configuration (60-75%) without any 4-substituted imidazole ribonucleoside. The structure of the 5-fluoroimidazole ribonucleoside was confirmed by X-ray crystallography and 2D NMR spectroscopy.

Regioselective glycosylation: synthesis of alpha-indoline nucleosides.

Novel indoline ribonucleosides with the alpha-N-glycoside configuration are synthesized with very high regioselectivity in 90-96%yield, using TMS protected indolines and 2,3-O-(1-methylethylidene)-5-O-(triphenylmethyl)-alpha/beta-D-ribofuranose. The structures of these ribonucleosides were elucidated with X-ray crystallography as well as 2D (NOESY, COSY, and HMQC) NMR spectroscopy.

UV-VIS spectroscopy of 2,4,6-trinitrotoluene-hydroxide reaction.

Contamination of groundwater, surface water and soil by explosives has occurred at military sites throughout the world as a result of manufacture of explosive compounds, assembly of munitions, and deployment of explosives containing devices. Due to the adverse effects of explosives on humans and other natural receptors, a low cost means of decontaminating these areas of contamination is needed. Base-induced transformation of explosives has shown promise as a rapid, low cost, and minimally resource-intensive technology for detoxifying explosives in soil and water.

Discrimination in resolving systems. VI. Comparison of the diastereomers of deoxyephedrinium and ephedrinium 4'-fluoromandelates.

(-)-(R)-Deoxyephedrine forms poorly discriminating diastereomeric salts with 4'-fluoromandelic acid from 95% ethanol. Both less-soluble (L) (S)-4'-fluoromandelate and more-soluble (M) (R)-4'-fluoromandelate phases are monoclinic and unsolvated. Their solubility ratio (M/L) in 95% ethanol is only 1.