Brønsted-Acid Catalyzed Diastereo- and Enantioselective Synthesis of Spiroisoindolinones from Enamides.

A highly stereoselective Brønsted-acid catalyzed synthesis of densely substituted spiroisoindolinones from enamides and 3-hydroxy-isoindolinones is described. With simple Brønsted-acids, such as para-toluene sulfonic acid, spiroisoindolinones with three contiguous stereogenic centers are formed in high yields (up to 97 %) and diastereoselectivities (up to >98 : <2 : 0 : 0 dr) under mild reaction conditions. With the use of a chiral phosphoric acid catalyst, a diastereo- and enantioselective synthesis of the corresponding spiroisoindolinones was achieved.

Brønsted Acid-Catalyzed Diastereoselective Synthesis of Spiroisoindolinones from Enamides.

A highly diastereoselective synthesis of spiroisoindolinones from enamides and 3-hydroxy-isoindolinones is reported. The reaction proceeds rapidly in the presence of -toluenesulfonic acid as a Brønsted acid catalyst and affords a variety of densely substituted spiroisoindolinones with three contiguous stereogenic centers in high yields (≤98%) and diastereoselectivities (up to dr >98:<2:0:0).

Unexpected Reduction of a Coordinated Diazapyridinophane Ligand Bound to Chromium(III) Ion Leading to Delocalization of the Unpaired Electron across Two Isolated Pyridine Units.

In the tetraazamacrocyclic ligand N,N'-dimethyl-2,11-diaza-[3.3](2,6)pyridinophane (L-N Me ), the two pyridine units are separated from each other by sp -hybridized triatomic bridges. Such electronically isolated pyridine moieties are considerably less prone to reductions than di- or triimines.

Palladium-catalyzed asymmetric three-component reaction between glyoxylic acid, sulfonamides and arylboronic acids for the synthesis of -arylglycine derivatives.

A palladium-catalyzed asymmetric three-component synthesis of -arylglycine derivatives starting from glyoxylic acid, sulfonamides and arylboronic acids is reported. This novel, operationally simple method offers access to the -arylglycine scaffold in good yields and enantioselectivities. The utilization of α tailored catalyst system enables the enantioselective synthesis of the desired -arylglycines despite a fast racemic background reaction.

A New Type of Valence Tautomerism in Cobalt Dioxolene Complexes - Temperature-Induced Transition from a Cobalt(III) Catecholate to a Low-Spin Cobalt(II) Semiquinonate State.

The synthesis and characterization of the monocationic cobalt(III) catecholate complex [Co(L-N Bu )(Cl cat)] (L-N Bu =N,N'-Di-tert.-butyl-2,11-diaza[3.3](2,6)pyridinophane, Cl cat =4,5-dichlorocatecholate) are presented.

Oxyenamides as Versatile Building Blocks for a Highly Stereoselective One-Pot Synthesis of the 1,3-Diamino-2-ol-Scaffold Containing Three Continuous Stereocenters.

A highly diastereoselective one-pot synthesis of the 1,3-diamino-2-alcohol unit bearing three continuous stereocenters is described. This method utilizes 2-oxyenamides as a novel type of building block for the rapid assembly of the 1,3-diamine scaffold containing an additional stereogenic oxygen functionality at the C2 position. A stereoselective preparation of the required (Z)-oxyenamides is reported as well.

Combining Structural with Functional Model Properties in Iron Synthetic Analogue Complexes for the Active Site in Rabbit Lipoxygenase.

Iron complexes that model the structural functional properties of the active iron site in rabbit lipoxygenase are described. The ligand sphere of the mononuclear pseudo-octahedral -(carboxylato)(hydroxo)iron(III) complex, which is completed by a tetraazamacrocyclic ligand, reproduces the first coordination shell of the active site in the enzyme. In addition, two corresponding iron(II) complexes are presented that differ in the coordination of a water molecule.

Iron(III)-Mediated Oxysulfonylation of Enamides with Sodium and Lithium Sulfinates.

An iron-mediated vicinal difunctionalization of enamides and enecarbamates with sulfinic acid salts and alcohols is described. This reaction proceeds under mild conditions and furnishes the oxysulfonylated products in moderate to excellent yields. Moreover, the direct incorporation of sulfur dioxide into the sulfonylated products via organolithium chemistry has been achieved.

Manganese(iii) acetate-mediated direct C(sp)-H-sulfonylation of enamides with sodium and lithium sulfinates.

A Mn(OAc)3 mediated oxidative C(sp2)-H sulfonylation of enamides and encarbamates with sodium and lithium sulfinates is reported. This operationally simple transformation provides a straightforward and highly stereoselective access to (E)-β-amidovinyl sulfones in moderate to excellent yields. The reaction proceeds readily under mild conditions at room temperature and tolerates various sensitive functional groups.

Mechanism of the Dehydrogenative Phenothiazination of Phenols.

The straightforward capture of oxidized phenothiazines with phenols under aerobic conditions represents a unique cross-dehydrogenative C-N bond-forming reaction in terms of operational simplicity. The mechanism of this cross-dehydrogenative N-arylation of phenothiazines with phenols has been the object of debate, particularly regarding the order in which the substrates are oxidized and their potentially radical or cationic nature. Understanding the selective reactivity of phenols for oxidized phenothiazines is one of the key objectives of this study.

The Strong β-CF Shielding Effect in Hexafluoroisopropanol and 100 Other Organic Solvents Revisited with O NMR Spectroscopy.

An O NMR spectroscopy survey of more than 100 ubiquitous organic solvents and compounds, including some typical oxofluorinated solvents such as hexafluoroisopropanol, trifluoroethanol, trifluoroacetic acid, and others, is presented with DO as a reference. A strong alternating α,β-CF-substituent chemical shift effect was thus observed. This alternating deshielding-shielding effect is suspected to have a role in the exceptional properties of these oxofluorinated solvents, notably in oxidative cross-coupling reactions.

The 1,6,7,12-Tetraazaperylene Bridging Ligand as an Electron Reservoir and Its Disulfonato Derivative as Redox Mediator in an Enzyme-Electrode Process.

The homodinuclear ruthenium(II) complex [{Ru(l-N Me )} (μ-tape)](PF ) {[1](PF ) } (l-N Me =N,N'-dimethyl-2,11-diaza[3.3](2,6)-pyridinophane, tape=1,6,7,12-tetraazaperylene) can store one or two electrons in the energetically low-lying π* orbital of the bridging ligand tape. The corresponding singly and doubly reduced complexes [{Ru(l-N Me )} (μ-tape )](PF ) {[2](PF ) } and [{Ru(l-N Me )} (μ-tape )](PF ) {[3](PF ) }, respectively, were electrochemically generated, successfully isolated and fully characterized by single-crystal X-ray crystallography, spectroscopic methods and magnetic susceptibility measurements.

Spectroscopic, Structural, and Kinetic Investigation of the Ultrafast Spin Crossover in an Unusual Cobalt(II) Semiquinonate Radical Complex.

A comprehensive spectroscopic and structural investigation of [Co (l-N  tBu )(dbsq)][B(p-C H Cl) ] (1, l-N  tBu =N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane, dbsq =3,5-di-tert-butylsemiquinonate), the first known octahedral complex with a low-spin (ls) Co semiquinonate ground state, is reported. Above 200 K, solids as well as solutions of 1 exhibit thermally induced spin-crossover (SCO) from the ls to the high-spin (hs) Co semiquinonate state instead of the frequently observed valence tautomerism from ls Co catecholate to hs Co semiquinonate.

Oxoanion binding to a cyclic pseudopeptide containing 1,4-disubstituted 1,2,3-triazole moieties.

A macrocyclic pseudopeptide 3 is described featuring three amide groups and three 1,4-disubstituted 1,2,3-triazole units along the ring. This pseudopeptide was designed such that the amide NH groups and the triazole CH groups converge toward the cavity, thus creating an environment well suited for anion recognition. Conformational studies in solution combined with X-ray crystallography confirmed this preorganisation.

Hepatic metabolism of carcinogenic β-asarone.

β-Asarone (1) belongs to the group of naturally occurring phenylpropenes like eugenol or anethole. Compound 1 is found in several plants, e.g.

Annulated and bridged tetrahydrofurans from alkenoxyl radical cyclization.

4-Pentenoxyl radicals sharing two or more carbon atoms with a cycloalkane cyclize in a predictable manner stereoselectively and regioselectively to afford in solutions of bromotrichloromethane cycloalkyl-fused or -bridged 2-bromomethyltetrahydrofurans in up to 95% yield. Stereoselectivity in alkenoxyl radical ring closures arises from cumulative steric effects. The substituent positioned the closest to the alkene carbon, which is being attacked by the oxygen radical, exerts the strongest stereodirecting effect.

How does a coordinated radical ligand affect the spin crossover properties in an octahedral iron(II) complex?

The influence of a coordinated π-radical on the spin crossover properties of an octahedral iron(II) complex was investigated by preparing and isolating the iron(II) complex containing the tetradentate N,N'-dimethyl-2,11-diaza[3.3](2,6)pyridinophane and the radical anion of N,N'-diphenyl-acenaphtene-1,2-diimine as ligands. This spin crossover complex was obtained by a reduction of the corresponding low-spin iron(II) complex with the neutral diimine ligand, demonstrating that the reduction of the strong π-acceptor ligand is accompanied by a decrease in the ligand field strength.

Bromidotetra-kis-(2-ethyl-1H-imidazole-κN (3))copper(II) bromide.

The Cu(II) ion in the title mol-ecular salt, [CuBr(C5H8N2)4]Br, is coordinated in a square-pyramidal geometry by four N atoms of imidazole ligands and one bromide anion in the apical position. In the crystal, the ions are linked by N-H⋯Br hydrogen bonds involving both the coordinating and the free bromide species as acceptors. A C-H⋯Br inter-action is also observed.

Paramagnetic palladacycles with Pd(III) centers are highly active catalysts for asymmetric aza-Claisen rearrangements.

A combination of spectroscopic and electrochemical methods--XANES, EXAFS, X-ray, (1)H NMR, EPR, Mössbauer, and cyclic voltammetry--demonstrate that the most efficient Pd catalysts for the asymmetric rearrangement of allylic trifluoroacetimidates unexpectedly possess in the activated oxidized form a Pd(III) center bound to a ferrocene core which remains unchanged (Fe(II)) during the oxidative activation. These are the first recognized Pd(III) complexes acting as enantioselective catalysts.

tert-Butyl 1-hy-droxy-piperidine-2-carboxyl-ate.

The title compound, C(10)H(19)NO(3), is a disubstituted piperidine bearing substituents in two equatorial positions. One of the substituents is a hy-droxy group bound to nitro-gen and the second a tert-butyl ester group bound to the carbon next to the endocyclic nitro-gen. Enanti-omers of the title compound form hydrogen-bridged dimers across a center of inversion.

Thermal spin-crossover in the [M(3)Zn(6)Cl(6)L(12)] (M = Zn, Fe(II); L = 5,6-dimethoxy-1,2,3-benzotriazolate) system: structural, electrochemical, Mössbauer, and UV-Vis spectroscopic studies.

Fusion of pentanuclear Kuratowski-type coordination units leads to homo- and heterononanuclear coordination compounds, two of which are presented, having structural formulae [Zn(9)Cl(6)(OMe(2)bta)(12)]·DMF (1), and [Fe(II)(3)Zn(6)Cl(6)(OMe(2)bta)(12)]·DMF (2), respectively; (OMe(2)btaH = 5,6-dimethoxy-1,2,3-benzotriazole; DMF = N,N'-dimethylformamide). Single crystal X-ray structure analyses reveal the presence of {M(3)Zn(6)L(12)}(6+) cores (M = Zn or Fe(II); L = 5,6-dimethoxy-1,2,3-benzotriazolate) in which the M(II) ions are bridged by μ(3)-OMe(2)bta ligands. In both compounds, the six peripheral Zn ions are tetracoordinated, whereas the remaining three metal ions M are hexacoordinated.

Iron chelates of 2,2'-bidipyrrin: stable analogues of the labile iron bilins.

A unique series of halogenidoiron(III) complexes of the open-chain tetrapyrrolic ligand 2,2'-bidipyrrin (bpd) ([FeX(bdp)] X=F, Cl, Br, I) was prepared from simple pyrrolic and bipyrrolic precursors and iron chloride by a one-pot condensation/metalation strategy, followed by salt metathesis with CsF, LiBr, or NaI. Crystallographic analysis revealed that in all cases the 2,2'-bidipyrrin ligand is forced to reside in a helical conformation when bound to the iron atom. Whereas the extremely sensitive fluorido derivative was isolated as a CsF adduct and forms 1D polymeric chains in the solid state, the more stable chlorido, bromido, and iodido derivatives crystallize as discrete monomeric molecules with a distorted pentacoordinate iron(III) ion in an intermediate spin ground state.