Intramolecular cyclization of acyl radicals onto the azido group: a new radical approach to cyclized lactams

[reaction: see text] Aryl- and alkyl-derived azidoacyl radicals, generated from thiolesters by intramolecular homolytic substitution at the sulfur, can undergo five- and six-membered cyclization onto the azido moiety to give cyclized lactams.     

Ruthenium dihydride complexes: NMR studies of intramolecular isomerization and fluxionality including the detection of minor isomers by parahydrogen-induced polarization

NMR studies reveal that complexes Ru(CO)(2)(H)(2)L(2) (L = PMe(3), PMe(2)Ph, and AsMe(2)Ph) can have three geometries, ccc, cct-L, and cct-CO, with equilibrium ratios that are highly dependent on the electronic properties of L; the cct-L form is favored, because the sigma-only hydride donor is located trans to CO rather than L. When L = PMe(3), the ccc form is only visible when p-H(2) is used to amplify its spectral features. In contrast, when L = AsMe(2)Ph, the ccc and cct-L forms are present in similar quantities and, hence, must have similar free energies; for this complex, however, the cct-CO isomer is also detectable. These complexes undergo a number of dynamic processes. For L(2) = dppe, an interchange of the hydride positions within the ccc form is shown to be accompanied by synchronized CO exchange and interchange of the two phosphorus atoms. This process is believed to involve the formation of a trigonal bipyramidal transition state containing an eta(2)-H(2) ligand; in view of the fact that k(HH)/k(DD) is 1.04 and the synchronized rotation when L(2) = dppe, this transition state must contain little H-H bonding character. Pathways leading to isomer interconversion are suggested to involve related structures containing eta(2)-H(2) ligands. The inverse kinetic isotope effect, k(HH)/k(DD) = 0.5, observed for the reductive elimination of dihydrogen from Ru(CO)(2)(H)(2)dppe suggests that substantial H-H bond formation occurs before the H(2) is actually released from the complex. Evidence for a substantial steric influence on the entropy of activation explains why Ru(CO)(2)(H)(2)dppe undergoes the most rapid hydride exchange. Our studies also indicate that the species [Ru(CO)(2)L(2)], involved in the addition of H(2) to form Ru(CO)(2)(H)(2)L(2), must have singlet electron configurations.     

Novel stereocontrolled addition of allylmetal reagents to alpha-imino esters: efficient synthesis of chiral tetrahydroquinoline derivatives

To prepare in multigram scale new antagonists of the glycine binding site associated to the NMDA receptor, an efficient distereoselective route was set up. The addition of suitable allyltin reagents to chiral N-aryl alpha-imino esters (R-(+)-tert-butyl lactate used as chiral auxiliary), gave the corresponding alpha amino acid-type derivative in high chemical yield and optical purity. This allylation reaction represents a novel example of efficient long-range stereodifferentiation process. In the last part of the synthesis, a regioselective Heck-type cyclization reaction enabled preparation of the target tetrasubstituted exocycle and trisubtituted endocycle double bond derivatives.     

Site-specific ligation of anthracene-1,8-dicarboxylates to an Mn12 core: a route to the controlled functionalisation of single-molecule magnets

A novel single-molecule magnet of the Mn12 family, [Mn12O12(O2CC6H5)8(L)4(H2O)4].8CH2Cl2, has been synthesised by site-specific ligand exchange using a tailor-made dicarboxylate (L2-), which leads to selective occupation of axial binding sites.     

Copper(II) complexes of N-terminal protected tri- and tetra-peptides containing histidine residues

Copper(II) complexes of peptides containing two or three histidyl residues (Ac-HisGlyHis-OH, Ac-HisGlyHis-NHMe, Ac-HisHisGlyHis-OH and Ac-HisHisGlyHis-NHMe) have been studied by potentiometric, UV-Vis, EPR and CD spectroscopic measurements. The imidazole nitrogen atoms are described as the primary metal binding sites of all ligands resulting in the formation of various macrochelates in the pH range 4 to 7. The (Nim, N-, Nim)-co-ordinated [CuH-1L]0+ complexes were mainly detected in samples containing free carboxylates at the C-termini, whilst the [CuH-2L]-(0) complexes were the predominant species in slightly alkaline solution and their binding modes were described via 4N-co-ordination (Nim, N-, N-, Nim) in (7,5,6)-membered fused chelate rings. Deprotonation and co-ordination of the third amide nitrogens were detected above pH approximately 9 in all cases.     

Synthesis and characterization of graphene‐containing thermoresponsive nanocomposite hydrogels of poly(N‐vinylcaprolactam) prepared by frontal polymerization

Thermoresponsive poly(N‐vinylcaprolactam) nanocomposite hydrogels containing graphene were successfully prepared by frontal polymerization. High concentration of graphene (5.0 mg/mL) was obtained by direct graphite sonication in the self‐same liquid monomer, thus avoiding any chemical manipulation and obtaining “real” graphene as nanofiller instead of one of its more or less oxidized derivative, which is what generally reported in published reports. Furthermore, the corresponding nanocomposites were obtained without using any solvent to be eventually removed. The materials were fully characterized by RAMAN, SEM, and TEM, and their swelling behavior and rheological properties were investigated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of novel 1,4‐dihydropyrido[3′,2′:5,6]thiopyrano[4,3‐c]‐pyrazoles and 5H‐pyrido[3′,2′:5,6]thiopyrano[4,3‐d]pyrimidines as potential antiproliferative agents

The synthesis of new planar derivatives characterized by the presence of a pyridothiopyranopyrazole or pyridothiopyranopyrimidine nucleus, carrying a substituted aryl group, is reported. The novel 1,4‐dihydropyrido[3′,2′:5,6]thiopyrano[4,3‐c]pyrazole derivatives were obtained by condensation of 2,3‐dihydro‐3‐hydroxymethylenethiopyrano[2,3‐b]pyridin‐4(4H)‐ones with appropriate hydrazines. The preparation of 2‐substituted pyrido[3′,2′:5,6]thiopyrano[4,3‐d]pyrimidines was accomplished from the intermediate 2,3‐dihy‐dro‐3‐dimethylaminomethylenethiopyrano[2,3‐b]pyridin‐4(4H)‐ones by reaction with the appropriate binucleophile amidines. The antiproliferative activity of some new products was tested by an in vitro assay on human tumour cell lines (HL‐60 and HeLa), but none of them showed any significant effects in the tests performed. Accordingly, linear flow dichroism measurements indicated their inability to form a molecular complex with DNA.     

Experimental and theoretical study of the interaction of CO2 with alpha-Al2O3

Density functional molecular cluster calculations are combined with X-ray photoelectron spectroscopy (XPS), quadrupolar mass spectrometry (QMS), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy to investigate the interaction of CO2 with alpha-Al2O3 and partially reduced alpha-Al2O3. The electronic structure of the stoichiometric and partially reduced substrate, adsorbate geometries, chemisorption enthalpies, and adsorbate vibrational parameters are computed and discussed. Theoretical results agree quite well with experimental data and previous theoretical investigations. As far as the adsorbate-substrate interaction is concerned, the results of our calculations indicate that CO2 forms bidentate-chelating carbonate species. The bonding scheme of this surface complex implies a significant substrate-->adsorbate transfer of charge (from the occupied dangling bond of a surface Lewis base site into one component of the CO2 2 pi u LUMO) assisted by a definitely weaker adsorbate-->substrate donation (from one component of the CO2 1 pi g HOMO into an empty dangling bond of a surface Lewis acid site). Our estimate of the chemisorption enthalpy (-15 kcal/mol) agrees quantitatively with calorimetric data reported for CO2 adsorbed on high surface area alpha-alumina (-16.0 kcal/mol). [Mao, C.-F.; Vannice, M. A. Appl. Catal. A 1994, 111, 151.] According to XPS and QMS outcomes, theoretical results predict that the interaction of CO2 with partially reduced alpha-Al2O3 gives rise to the reduction of the adsorbate to CO and to the concomitant substrate reoxidation.