Giovanni Valle

Acid-catalysed addition of N-aryl imines to dihydrofuran. Postulated dependence of the reaction mechanism on the relative face of approach of reactants

Imines 1a and 1b react with dihydrofuran (DHF) under Lewis acid catalysis via Diels–Alder-type addition to form the tetrahydroquinoline derivatives 3a, b and 4a, b. Besides these compounds, the methanol adduct 2 of 1a, or 1a in the presence of methanol, gives the methanol-containing tetrahydrofuran derivative 7a and the hexahydrofuro[3,2-b]furan derivatives 5 and 6. In the presence of methanol, 1b gives 3b and 4b, and also 7b and 8. The products 3a, b, 5, 6 and 7a, b originate from approach of the Si(or Re) face of 1a, b onto the Si(or Re) face of DHF; 4a, b and 8 derive from interaction of the Si(or Re) face of 1a, b with the Re(or Si) face of DHF. The dependence of the product distribution on the polarity of the solvent suggests that a concerted mechanism predominates in the former mode and a zwitterionic one in the latter. In the addition of 1a or 2 the mechanistic preference may be exclusive.

Oxidations with peroxotungsten complexes: rates and mechanism of stoichiometric olefin epoxidations

Abstract The stoichiometric epoxidation reactions of a series of olefins with WO-(O2)2HMPT and MoO(O2)2HMPT have been studied in dichloroethane at 40 °C. The data obtained point out the superior oxidizing ability of W(VI) over Mo(VI). However, the two peroxo groups in WO(O2)2HMPT appear to react with the substrates at different rates, the transfer of the first peroxide oxygen being faster than of the second one, contrary to that observed in the behavior of MoO(O2)2HMPT. The crystal structure of WO(O2)2HMPT·H2O, determined by diffractometric techniques, does not show any significant difference compared to that reported for MoO(O2)2HMPT·-H2O, indicating that it might be difficult to correlate the solid state structures with the different behaviors experimentally observed in solution. In spite of the different features shown by the two peroxo complexes, the data collected in this investigation suggest that an identical mechanism of oxygen transfer from the two oxidants is operating. Moreover, this mechanism should not involve the occurrence of substrate-oxidant intermediates.

The speciation of aluminum in aqueous solutions of aluminum carboxylates. Part I. X-ray molecular structure of Al[OC(O)CH(OH)CH3]3

Abstract The crystal structure of tris(2-hydroxypropanoate-(L))aluminum(III) was determined by X-ray crystallography and refined to R=0.044. The molecular structure is uncomplicated and contains monomeric [Al(lact)3]entities, in which the metal atom is surrounded by a distorted octahedral {O6} coordination sphere where the oxygen atoms of the carboxylate and of the hydroxyl group are the donating sites. The major source of the geometrical distortion is in the OAlO angles of the metallo-organic ring (c83°. The AlO distances range from 1.86 to 1.91 A. All hydroxyl hydrogen atoms are involved in very tight intermolecular hydrogen bonds (c. 2.50 A) which involve the carbonyl groups of adjacent Al(lact)3 unities. The solid state IR spectrum of Al(lact)3 is interpreted in terms of monohapto ‘end on’ coordination of the carboxylate donating site to AlIII.

SYNTHESIS OF STRUCTURALLY MODIFIED ATROPISOMERIC BIARYL DITHIOLS. OBSERVATIONS ON THE NEWMAN-KWART REARRANGEMENT

Abstract The preparation of a number of biaryldithiols from biaryldiols is discussed. A key reaction is the Newman-Kwart thermorearrangement of bisthiocarbamates and crucial variables of temperature and reaction time have been identified. Alternative approaches to 3,3′-disubstituted dithiols via ortho metallation are presented. The benefit of using such disubstituted compounds is illustrated with representative examples of the stereochemical features of the derived carbanions in reactions with prochiral electrophiles.

Synthesis, molecular structure and reactivity of sodium 5-sulfosalicylate dihydrate and sodium[triaqua(5-sulfosalicylato)copper(II)] 2 hemihydrate

Abstract The crystal and molecular structure of sodium 5-sulfosalicylate dihydrate, Na[(H2Ssal)(H2O)2], (1) (H3Ssal=5-sulfosalicylic acid) has been determined through X-ray diffraction analysis. The 5-sulfosalicylate anion has lost the proton at the SO3H group but retains the usual intermolecular hydrogen bond between phenolic and carboxylic oxygen. The reaction in water of 1 with [Cu(II)(H2O)4]SO4·H2O, gives rise to the green sodium[triaqua(5-sulfosalicylato)copper(II)] 2 hemihydrate, Na[(H2O)3(Ssal)Cu(II)]·2×0.5H2O, (2). The 5-sulfosalicylate anion, (Ssal3−), coordinates rather unusually in the syn–syn coordination mode since it binds bidentately the Cu(II) ion through the carboxylic and the phenolic oxygens, with Cu(II)Ocarboxylic=1.909(4) A and Cu(II)Ophenolic=1.885(4) A distances. Copper(II) completes its square-planar coordination with two water molecules and in addition, perpendicularly to the square-planar coordination plane, another two water molecules with long bonds are present (Cu(II)O=2.518 and 2.912 A). The green complex 2 reacts easily with adenine in water at pH 7 giving rise to the violet tetraadeninato(diaqua)-bis(copper(II)) dihydrate, [Cu2(Ade)4(H2O)2])]·2H2O, (3) (Ade−=adeninato monoanion). This complex, that geometrically resembles copper(II) acetate monohydrate, was already described by Sletten. Finally, on the basis of the present results a possible mechanism for the anticancer activity of complex 2 and of other Cu(II)–salicylate complexes is proposed and discussed.

Phthalimidosulfenyl chloride. Part 5. Reaction with enolizable carbonyl compounds and synthesis of functionalized thiones.

Abstract β-Ketothio derivatives 4, prepared by reaction of phthalimidosulphenyl chloride with enolizable carbonyl compounds, afford, in presence of pyridine, unstable functionalized thiones which can be trapped with 1,3-dienes to give the corresponding cycloaddition products 8 and 9.

Bioactive and model peptides characterized by the helicogenic (αMe)Phe residue

Abstract We have synthesized and fully characterized the hypersweet super-aspartame analogue p CN-C6H4-NHCO-L-Asp-L-(αMe)Phe-OME 1; the [D-(αMe)Phe]3-analogue of the formyl-methionyl tripeptide chemoattractant HCO-L-Met-L-Leu--D-(αMe)Phe-OMe 2, the first D-chemotactic peptide being found more active than its L-diastereomer; and the model pentapeptide p BrBz-D-(αMe)Phe-(Aib)2-D-(αMe)Phe-Aib-O t Bu 3. The preferred conformation of the three peptides, as determined by X-ray diffraction analyses, is discussed in terms of the proposed receptor models for sweet perception [peptide 1] and neutrophil chemotaxis [peptide 2], and as a promising candidate for molecular recognition studies [peptide 3].

Co-ordination chemistry of adenine (HAde): synthesis and characterization of [CuII(tren)(nucleobase)]X2[tren = tris-(2-aminoethyl)amine, X = Cl or NO3] complexes and crystal structure of [CuII(tren)(Ade)]Cl·2H2O

The five-co-ordinate complexes [CuII(tren)(H2O)]Cl21, [CuII(tren)(HAde)]Cl22, [CuII(tren)(HAde)]-[NO3]23 and [CuII(tren)(Ade)]Cl·2H2O 4[tren = tris(2-aminoethyl)amine and HAde = neutral adenine] have been synthesized and characterized. The geometry and structures of the complexes were studied by electronic and IR spectra and, in addition, the structure of complex 4 has been determined by X-ray crystallography. The physicochemical data for complexes 2 and 3 support the presence of neutral adenine co-ordinated to CuII, whereas in complex 4 the adenine molecule is bound in its monoanionic form, as confirmed by the X-ray analysis [monoclinic, space group P21/a, a= 15.001(2), b= 8.422(1), c= 15.039(2)A, β= 105.90(6)°, Z= 4; R= 0.065 for 2596 unique diffraction data]. The co-ordination polyhedron around the Cu2+ ion is approximately trigonal bipyramidal, with the equatorial sites occupied by the three primary amino nitrogen atoms and the axial positions occupied by the tertiary amino nitrogen and the imidazole N9 nitrogen from the adenine monoanion. The Cu–N(9) distance is rather short at 1.965(9)A. Such selective metal bonding in adenine is very probably promoted by the trigonal-bipyramidal geometry around CuII and by the relatively low steric hindrance of the CuII(tren) moiety.

Dinuclear gold(I) and silver(I) derivatives with bridging phosphines containing an imidazole ring; X-ray crystal structure of (1-benzyl-2-imidazolyl)diphenylphosphinegold(I)chloride.

Abstract (1-Benzyl-2-imidazolyl)diphenylphosphine [(BzIm)Ph 2 P] can act as a monodentate or bidentate ligand to afford mononuclear (BzIm)Ph 2 PAuCl ( I ) or dinuclear [μ-(BzIm)Ph 2 PAu] 2 2+ 2X − (X = PF 6 − , BF 4 − or NO 3 − ) ( IIa,b,c ) derivatives of gold(I). Analogous dinuclear silver(I) derivatives were obtained reacting the ligand [(BzIm)Ph 2 P] with AgX salts (X = NO 3 − , BF 4 − ) ( IIIa,b ). In solution the silver complexes show a fluxional behaviour, and two conformers were observed by 31 P NMR spectroscopy. The structure of compound I was established by X-ray crystallography (monoclinic, space group C2/c, a = 18.068(2), b = 16.576(2), c = 15.391(2) A , β = 117.2(2)°, Z = 8) . The short intermolecular Au⋯Au distance of 3.03(2) A indicates a metal-metal interaction. The 197 Au Mossbauer parameters of compounds I and IIa are consistent with IR, NMR and crystallographic data.

A Mössbauer study of some iron(II) and iron(III) poly(pyrazolyl)borates. The x-ray crystal structures of iron(II)bis[hydridotris(3-methyl-1H-pyrazol-1-yl)borate] and iron(II)bis[hydridotris(1H-pyrazol-1-yl)borate] tetrafluoroborate

Abstract A series of iron(II) or iron(III) complexes of type FeL2 or [FeL2]+ X−(X = BF4 or BPh4) with L = hydridotris(1H-pyrazol-1-yl)borate(L0), tetrakis(1H-pyrazol-1-yl)borate(L0′), hydridotris(-methyl-1H-pyrazol1-yl)borate(L1), hydridotris(3,5-dimethyl-1H-pyrazol-1-yl)borate(L2), hydridotris(4-chlor-3,5-dimethyl-1H-pyrazol-1-yl)borate(L2Cl), hydridotris(3,4,5-trimethyl-1H-pyrazol-1-yl)borate(L3), hydridotris(1,2,4-1H-triazol-1-yl)borate(Ltz) and hydridotris(3a,7a-benzo-1,2,3-1H-triazol-1-yl)borate(Lbtz) has been prepared. The series has been characterized mainly by th 57Fe Mossbauer effect. The X-ray crystal structures of iron(II)bis[hydridotris(3-methyl-1H-pyrazol-1-yl)borate] (3) and iron(III)bis[hydridotris(1H-pyrazol-1-yl)borate] tetrafluroborate (9) have been resolved. Discrete units with octahedral FeIIN6 or FeIII sites are present in each. The Fen bond length ranges from 2.197(4) to 2.215(4) A in 3 and from 1.948(6) to 1.964(6) A in 9. The bond angle ranges from 86.4(2)° to 93.7(2)° in 3 and from 88.3(4)° to 90.9(5)° in 9.