Paolo Sgarabotto

Radical annulations and cyclisations with isonitriles: the fate of the intermediate imidoyl and cyclohexadienyl radicals

Abstract The reaction of 4-methoxyphenylisonitrile with phenylacetylene and AIBN produces a novel cyclopenta-fused quinoxaline through addition of 2-cyanoprop-2-yl radical to the alkyne; the resulting vinyl radical attacks isonitrile to afford an imidoyl radical, which gives rise to a tandem 5-exo, 6-endo cyclisation. The whole process entails a new example of a rare 4 + 1 radical annulation. The cyanopropyl radical can also attack isonitrile to yield small amounts of quinolines deriving from 4 + 2 and 3 + 2 annulation between the resulting imidoyl radicals and phenylacetylene. The oxidation step leading to the final aromatic products involves the starting isonitrile, which is converted to an α-unsubstituted imidoyl radical and affords 2-unsubstituted quinolines. This behaviour was also found in cyclisations of biphenyl-2-ylisonitrile under various radical conditions. Finally, the title reaction gives small amounts of an α,β-unsaturated nitrile, which can arise from a spirocyclohexadienyl radical through fragmentation and subsequent β-scission of the resulting iminyl. This could be the first, direct evidence of the intermediacy of iminyl radicals in the rearrangements of the spirocyclohexadienyls obtained by 3 + 2 annulation between imidoyl radicals and alkynes.

Preparation, characterization and activity of palladium(II) halide complexes with diethyl 8-quinolylmethylphosphonate (8-dqmp). X-ray crystal structure of [8-dqmpH]2[PdCl4]·2H2O and [8-dqmpH]2[Pd2Br6]

Abstract The synthesis, spectroscopic and biological properties of the novel palladium(II) halide complexes with diethyl 8-quinolylmethylphosphonate (8-dqmp) have been reported. It was shown that the square planar complexes trans-[Pd(8-dqmp)2X2] were obtained by reaction of 8-dqmp with PdX42− (XCl, Br) in the neutral ethanolic/aqueous solution. In the HX acidic medium the quinolinium salt complexes [8-dqmp H]2[PdX4] were isolated. They were converted by heating in methanol into the corresponding hexahalodipalladium salt complexes [8-dqmpH]2[Pd2X6]. The new complexes were characterized on the basis of elemental and thermogravimetric analysis, magnetic and conductance measurements, by the IR and 1H NMR spectra and some X-ray crystal structure determinations. The complexes were tested for their cytostatic activity on KB and L1210 cell lines. The coordination behaviour of 8-dqmp as well as the spectral and biological properties of its complexes were compared with the results reported for the diethyl ester of 2-quinolylmethylphosphonic acid (2-dqmp) and its palladium(II) halide complexes. The molecular structures of the complexes [8-dqmpH]2[PdCl4]·2H2O (3) and [8-dqmpH]2[Pd2Br6] (6) have been fully characterized by X-ray diffraction studies. The crystals of both complexes are triclinic, space group P1, Z=2, with lattice parameters for 3: a=9.438(2), b=9.481(2), c=11.082(2) A, α=83,4(1), β=107.5(1), γ=77.0(1)°, the final R factors are R=0.0481 and R′=0.0551 for 3208 observed diffractometer collected reflections; and for 6: a=11.943(2), b=10.644(2), c=8.873(2) A, α=102.08(2), β=85.56(2), γ=69.54(2)°, the final R factors are R=0.0725 and R′=0.0804 for 2584 observed diffractometer collected reflections. The structure of 3 is composed of the square planar PdCl42− anion lying in a centre of symmetry (average PdCl=2.330 A), of two quinotinium phosphonate cations and two water molecules. The structure of 6 consists of two quinolinium moieties as a cationic part separated by the Pd2Br6 centrosymmetric dianionic dimer.

STRUCTURAL AND ELECTRICAL CHARACTERIZATION OF POLYMERIC HALOPLUMBATE(II) SYSTEMS

The synthesis and the structural, thermal, and electrical characterization of haloplumbate(II) systems are described. The counterions are diprotonated linear aliphatic amines, such as the 2-methylpentane-1,5-diamine (2meptH2) and propane-1,3-diamine (pnH2) dications. The (2meptH2)[PbCl4] and (2meptH2)[PbBr4] are isostructural, space group Cc, with a = 24.140(4) A, b = 7.720(2) A, c = 7.795(2) A, β = 98.1(1)°, Z = 4 for the chlorine compound and a = 24.539(4) A, b = 8.031(2) A, c = 8.198(2) A, β = 99.6(1)°, Z = 4 for the bromine compound; the (2meptH2)[Pb1.5I5] crystallizes in the triclinic P1 space group, with a = 11.803(3) A, b = 12.565(3) A, c = 8.494(8) A, α = 106.2(1)°, β = 100.5(1)°, γ = 117.4(1)°, Z = 2; the crystals of (pnH2)[PbCl4] are orthorhombic, space group P212121, a = 19.247(4) A, b = 7.862(2) A, c = 7.581(2) A, Z = 4; the (pnH2)2[Pb1.5Br7]·H2O crystallizes in the triclinic P1 space group, with a = 11.517(3) A, b = 14.122(3) A, c = 8.149(2) A, α = 104.1(1)°, β = 109.8(1)°, γ = 77.5(1)°, Z ...

Hydrogen bonding in thiosemicarbazide

In a recent paper (Domiano, Fava Gasparri, Nardelli & Sgarabotto, 1969, DGNS) the crystal-structure analysis of thiosemicarbazide, carried out by photographic methods, was reported (final R=9 .9%) . The positions of the hydrogen atoms were postulated from consideration of the hybridization of the nitrogen atoms and the packing interactions, no direct determination of position being possible from the final difference synthesis. In order to obtain a more accurate structure analysis, suitable for the location of the hydrogen atoms, new data have been collected at room temperature with an automated Picker diffractometer.

Stereochemistry of cercosporin

Abstract The absolute configuration of the asymmetric carbons and the axial chirality of the natural mold metabolite cercosporin (from Cercospora sp .) have been established on the basis of X-ray analysis and chemical reactions. The results confirm the inherent dissymmetry of the perylenequinone ring, the twisting of which gives rise to the diastereoisomer isocercosporin. The energy barrier for the conversion of cercosporin into isocercosporin has been evaluated.

Coordination properties of N-p-tolylsulfonyl-l-glutamic acid toward metalII: Part 1. Crystallographic study on ZnII and CdII complexes

Abstract A series of compounds of N-p-tolylsulfonyl- l -glutamic acid with divalent Cu, Zn and Cd are synthesized and characterized. For the complexes [Zn(tsgluO)(H2O)2]·H2O (1), [Cd2(tsgluO)2(H2O)6] (2) and [Cd(bipy)(tsgluO)] (3) the crystal and molecular structure have been determined by X-ray diffraction (tsgluO=N-p-tolylsulfonyl- l -glutamate dianion, bipy=2,2′-bipyridine). In compound 1 the ZnII ion exhibits a tetrahedral geometry arising from coordination of two carboxylic oxygens of two amino acid molecules and of two water molecules. In compound 2 each CdII ion of the dimeric unit is coordinated by oxygen atoms of tsgluO2− and water molecules in a distorted octahedral environment. In compound 3 the CdII ion is coordinated by 2,2′-bipyridine nitrogens and four oxygen atoms from three different tsgluO2− in a distorted octahedral geometry.

SYNTHESIS, X-RAY CRYSTAL STRUCTURES AND CHARACTERIZATION OF COPPER(II)-2,2'-BIPYRIDYL DERIVATIVES OF (4-AMINO)-HIPPURIC ACID AND OF L-PROLINE

Abstract In this paper the synthesis and the characterization of two complexes of copper and 2,2′-bipyridyl with amino acids 4-aminohippuric acid and l -proline are reported. The X-ray structure reveals for the first complex, [Cu2(OH)(OH2)(bipy)2(Am-hip)](NO3)2·4H2O, dinuclear copper(II) cations with nitrate counterions and lattice water molecules. The two metal centres are linked together by a water molecule, a hydroxyl group and the carboxylic moiety of the 4-amino-hippuric acid, the remaining two positions on both metal centres are occupied by bipyridyl molecules. The second compound consists of monomeric [Cu(OH2)(bipy)( l -pro)]+ cations and perchlorate anions. Also in this case copper is five-coordinated in a distorted square pyramidal geometry with the bipyridine nitrogens, one carboxylate oxygen atom and the amino nitrogen of the l -proline ion on the basal plane.

ORGANIC/INORGANIC COMPOSITE MATERIALS : SYNTHESIS AND PROPERTIES OF ONE-DIMENSIONAL POLYMERIC HALOPLUMBATE(II) SYSTEMS

Abstract In this paper we report the synthesis and the thermal, spectroscopic and electrical characterization of 1-D polymeric haloplumbates(II) of formula (A) [PbX3] (A = piperidinium] (pdH), morpholinium (mpH) cation; X = Br, I for pdH and Cl, Br for mpH). For the morpholinium compounds we report also the structural analysis. The (mpH) [PbX3] (X = Cl, Br) complexes are isomorphous and crystallized space group P212121. The unit cell dimensions are a = 15.249(3), b = 8.001(2), c = 7.625(2) A , V = 930.3(4) A 3 , Z = 4 for (mpH) [PbCl3] and a = 15.760(3), b = 8.254(2), c = 7.866(6) A , V = 1023.2(4) A 3 , Z = 4 for (mpH) [PbBr3]. The final R value is 0.0428 (Rw = 0.0442) for (mpH) [PbCl3] and 0.0434 (Rw = 0.0453) for (mpH) [PbBr3]. The structure consists of morpholinium cations and infinite polymeric anions [PbX3−]n; each lead atoms is surrounded by six halogen atoms forming a strongly distorted octahedronl adjacent octahedra share faces to form 1-D endless chains in which two consecutive lead atoms are bridged by three halogen atoms. The distortion in the (PbX6) octahedra of (mpH) [PbX3] enables the metal ion to be involved in a semicoordinative bond with the oxygen atom of the morpholinium cation, which makes the lead(II) coordination 6 + 1. All the structures are tridimensionally built up by a network of intermolecular NH⋯X bonds.

Unexpected Deoxygenation of 2,2,6,6-Tetramethylpiperidine-1-Oxyl (TEMPO) by Thiyl Radicals through the Formation of Arylsulphinyl Radicals

Abstract 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO), upon reaction with thiophenols, undergoes deoxygenation leading mainly to the formation of tetramethylpiperidinium arylsulphinates and arylsulphonates. Other identified products of the reaction are aryldisulphides, 2,2,6,6-tetramethylpiperidine, S-arylarylthiosulphonates, N-arylsulphinyl- and N-arylsulphonyl-2,2,6,6-tetramethyIpiperidine. The formation of the reaction products is discussed on the basis of the interaction of arylsulphinyl and arylsulphonyl radicals with TEMPO as well as on the basis of the evolution of the arylsulphinyl radical itself.

Homolytic substiution in indolinone nitroxides- IV. Reactions with aminyl radicals. A spectroscopic and crystallographic study

Abstract The reactions between 2,2-diphenyl-indolinone-N-oxyl (3) and a series of aminyl radicals generated in situ by oxidation of secondary aromatic amines with PbO2 lead to animated hydroxylamines (4), which in the presence of PbO2 are converted to the aminated nitroxides (5). When starting from primary amines, these are further oxidated to quinonimine-N-oxides (6) which then undergo nucleophilic substitution by another amine molecule to give the diaminated hydroxylamines (7). These are further oxidated to nitroxides (8), the final products of the reaction being the aminated quinone-diimine-N-oxides (9). The paramagnetic species (5) and (8) have been characterized using ESR spectroscopy; in addition, the molecular geometry of one of the N-oxides (9) was elucidated by means of X-ray structure analysis.