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Mononuclear amino triphenolate iron(III) complexes have been synthesized and characterized (UV/Vis spectroscopy, cyclic voltammetry, ESI-MS, 1H NMR spectroscopy, X-ray diffraction). These complexes act as biomimetic catalysts promoting the aerobic auto-oxidation of 3,5-di-tert-butylcatechol to the corresponding o-benzoquinone at room temperature and displaying catalase activity for the hydrogen peroxide dismutation with remarkable activity (TON up to 4000).

Six cyclometalated iridium(III) complexes were investigated to assess their potential as photosensitizers for long-range electron transfer, and two of them were incorporated directly into covalent donor–bridge–acceptor molecules. The influence of ligand substitutions on the excited-state properties and the photoredox behavior of the iridium complexes was explored by optical absorption, steady-state and time-resolved luminescence spectroscopy, as well as by electrochemical methods. Bimolecular electron transfer between the photoexcited complexes and 10-methylphenothiazine and methylviologen was found to be only weakly dependent on the ligand substitutions. Intramolecular long-range electron transfer from phenothiazine to photoexcited iridium(III) in the dyads is slow due to the occurrence of a Coulomb barrier. Consequently, an electron-transfer photoproduct is only observable in the transient absorption spectrum of a donor–bridge–acceptor molecule with a fluorinated photosensitizer that exhibits a very long excited-state lifetime. A flash-quench technique is necessary for detection of an electron-transfer product in the dyad with a non-fluorinated photosensitizer. The occurrence of a Coulomb barrier associated with intramolecular (excited-state) long-range electron transfer in the dyads with cyclometalated iridium(III) photosensitizers represents an important difference to previously investigated similar donor–bridge–acceptor molecules with photosensitizers based on d6 metal diimine complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Chiral framework: Chiral amines with pyrrolidine frameworks catalyze the enantioselective conjugate addition of a wide range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to99 % ee (see scheme). The high versatility of the Michael adducts is exemplified by various functionalizations with conservation of the optical purity.Chiral amines with a pyrrolidine framework catalyze the enantioselective conjugate addition of a broad range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to99 % ee. This novel process provides synthetically useful chiral gamma-gem-sulfonyl or phosphonyl aldehydes which can be widely functionalized with retention of the enantiomeric excess. Mechanistic insights including DFT calculations are explored in detail.

The highly tuned, one-point binding cationic cyclopentadienyl-iron and -ruthenium complexes 1 and 2 that incorporate chiral bidentate pentafluoroaryl-phosphinite ligands selectively coordinate and activate alpha,beta-unsaturated carbonyl compounds towards asymmetric catalytic cycloaddition reactions with diaryl nitrones. The reaction gives isoxazolidine products in good yields, with complete endo selectivity and high enantioselectivity. The products are obtained as a mixture of regioisomers in ratios varying from 96:4 to 15:85. The regioselectivity correlates directly with the electronic properties of the nitrone. This is shown by the experimental and computational data.

We report on the preparation of discrete 3D tetrametallic edifices containing trivalent lanthanides (Eu-Lu). Their formation is thermodynamically controlled through self-assembly with a new tripodal ligand L possessing short binding strands. X-ray crystallography shows that four nine-coordinate cations adopt a regular tetrahedral arrangement in the solid state. These remarkable, highly charged structures are maintained in solution, as demonstrated by NMR spectroscopy, ESI-MS and spectrophotometry. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Recently we have demonstrated a series of systems in which complex structures were created from simple amine and aldehyde subcomponents by copper(I)-templated imine bond formation. We describe herein the extension of this "subcomponent self-assembly" concept to the generation of structures based upon the iminoboronate ester motif. Equimolar amounts of diol, amine, and 2-formylphenylboronic acid reacted by reversible B-O and C=N bond formation to generate iminoboronate esters, as has recently been reported by James et al. (Org. Lett. 2006, 8, 609-612). The extent of ester formation was shown to depend upon a number of factors. The exploration of these factors allowed rules and predictions to be formulated governing the self-assembly process. These rules allowed the construction of more complex structures containing multiple boron atoms, including a trigonal cage containing six boron centers, as well as pointing the way to the construction of yet more intricate architectures. The lability of the B-O and C=N bonds also allowed different diol and amine subcomponents to be substituted within these structures. Selection rules were also determined for these substitution reactions, allowing the products to be predicted based upon the electronic properties of the diols and diamines employed. These results thus demonstrate the generality of the subcomponent self-assembly methodology through its application to a new dynamic covalent system.

Mannose-derived hexacoordinated phosphate anions, prepared in as few as two steps from methyl-alpha-D-mannopyranoside and tris(dimethylamino)phosphine, are chiral anionic auxiliaries with broad asymmetric efficiency. These chemically robust anions are effective NMR chiral solvating agents and efficient asymmetry-inducers, able to control the configuration of conformationally labile C2-symmetric monomethinium cations (organic, helical, charge 1+, P or M enantiomers) and D3-symmetric iron(II) trisdiimine complexes (metallo-organic, octahedral, charge 2+, Delta or Lambda enantiomers). Diastereomeric control with often unmatched selective levels was achieved with the help of mannopyranoside backbone of the anions and the substituents on the [1,3]dioxane ring that play a key role in the recognition process, something not obvious at first sight.

Bring on the big cats: New, C2-symmetric bulky N-heterocyclic carbene ligands bring major improvements in the palladium-catalyzed asymmetric intramolecular α-arylation of amides to give oxindoles (see picture, dba=trans,trans-dibenzylideneacetone), which are formed in high yield and excellent enantiomeric purity.

Bis-iminophosphoranes containing various types of linkers between two R3PN moieties were electrochemically oxidized at controlled potential in situ in the electron spin resonance (ESR) cavity. For linkers constituted of phenylenes, conjugated phenylenes or merely a dicyanoethylenic bond, this oxidation led to well-resolved ESR spectra which were characterized by their g values and by their 1H, 14N and 31P isotropic hyperfine constants. These coupling constants agree with those calculated by DFT for the corresponding cation radicals. Experimental and theoretical results clearly indicate that in these species the unpaired electron is mostly delocalized on the bridge and on the nitrogen atoms while the spin density on the phosphorus atoms is particularly small. Cyclic voltammetry and ESR spectra show that the nature of the bridge between the two iminophosphoranes considerably influences the oxidation potential of the compound as well as the stability of the radical cation. Information about the conformation of the precursor containing two Ph3PN moieties separated by a C(CN)C(CN)group was obtained from its crystal structure. Copyright © 2007 John Wiley & Sons, Ltd.

The complex [Cu₂(1)₂]²⁺ (1 = 1,3‐bis(1‐methyl‐1H‐benzimidazol‐2‐yl)benzene) undergoes slow oxidation by dioxygen in DMF solution to give the hydroxylated product [Cu₂(2‐H)₂]²⁺ (2 = 2,6‐bis(1‐methyl‐1H‐benzimidazol‐2‐yl)phenol) characterized by an X‐ray crystal‐structure analysis. The oxidation occurs much faster when CuII is mixed with 1 in the presence of H₂O₂, with 80% hydroxylation observed within a few minutes. The mononuclear complex formed with 1‐methyl‐2‐phenyl‐1H‐benzimidazole (3) shows no hydroxylation under these conditions. It is concluded that the hydroxylation requires the presence of a ligand capable of stabilizing a binuclear species, but no special coordinative activation of the copper is required.

For 25 years it has been known that 1,4-dihydroxynaphthalene and tetrahydronaphthalene-1,4-dione coexist as stable tautomers; however, the dione has now emerged as an interesting starting material for synthesis. Its efficient isolation is reported, and the corresponding [Cr(CO)3] complexes of the two tautomers are prepared, thus leading to efficient desymmetrization using chiral diamine acyl-transfer catalysts

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The title compound (±)-1, a recently discovered, valuable, floral-type odorant, has been synthesized by a straightforward procedure (Scheme 1). To determine the properties of the enantiomers of 1, their separation by preparative HPLC and the determination of their absolute configuration by X-ray crystallography were carried out (Figure). Furthermore, the analogues 2–6 were synthesized, either from differently methylated 2-methylindan-1-ones (Schemes 2 and 3) or, in the case of the 2,4,6-trimethylated homologue 6, by a completely different synthetic approach (Scheme 4). An evaluation of (+)-(S)-1, (−)-(R)-1, and (±)-1 showed only minor differences in terms of odor (Table).

Placing fluorine atoms at selected positions allows enantiopure hexacoordinate phosphate anions to behave as effective chiral solvating and resolving agents for RuII complexes (the structure of one of the anions is shown: F: yellow; O: red; Cl: green; P: purple). The structural features of the asymmetric ion pairing can be determined by NMR spectroscopy owing to the presence of the fluorine atoms. Fluoratome an ausgewählten Positionen machen enantiomerenreine hexakoordinierte Phosphatanionen zu effektiven chiralen solvatisierenden und trennenden Agentien für RuII-Komplexe (die Struktur eines Anions ist gezeigt: F: gelb; O: rot; Cl: grün; P: violett). Die Strukturmerkmale der asymmetrischen Ionenpaarung können wegen der Fluoratome NMR-spektroskopisch bestimmt werden.

The aminal of (benzaldehyde)tricarbonylchromium and en-antiopure bipyrrolidine undergoes diastereoselective ortho-metallation with butyllithium. Quenching with various electrophiles, followed by hydrolysis of the aminal, affords ortho-substituted (benzaldehyde)tricarbonylchromium compounds with high ee (91–99 %). When quenched with Ph2PCl, a new chiral P,N-bidentate ligand is obtained, which shows efficiency in Pd- and Cu-catalysed reactions. The aminal of ferrocenecarbaldehyde could also be formed, but the ortho-deprotonation occurs with only moderate diastereoselectivity (70 %). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Under stoichiometric conditions, the segmental tris-tridentate ligand L9 assembles with two different lanthanide metal ions Ln(1) and Ln(2) (Ln(1), Ln(2)=La, Nd, Sm, Eu, Yb, Lu, Y) to give mixtures of the heterotrimetallic triple-stranded helicates [(Ln(1))(x)(Ln(2))(3-x)(L9)(3)](9+) (x=0-3) in acetonitrile. The combination of qualitative (ESI-MS) and quantitative ((1)H NMR) speciations provides a set of thermodynamic data that were analysed with various statistical chemical models. A satisfying description requires the consideration of different affinities for the terminal N(6)O(3) sites (k(t)(Ln) and for the central N(9) site (k(c)(Ln) for each specific lanthanide. The nontrivial dependence of these parameters on the ionic radius provides size-discriminating effects that favour the formation of heterotrimetallic helicates in which the central site is occupied by the larger metal of the pair. Combining the latter enthalpic driving forces with entropic contributions due to specific stoichiometric conditions allows partial selection (i.e., programming) of a specific heterotrimetallic species in solution, which can be isolated by crystallisation, as demonstrated for [Eu(2.04)La(0.96)(L9)(3)](CF(3)SO(3))(9)(CH(3)NO(2))(9) (1, Eu(2.04)La(0.96)C(207)H(222)N(48)O(51)S(9)F(27), monoclinic, P2(1)/c, Z=4) in which the cation [EuLaEu(L9)(3)](9+) is the major component in the crystal. The scope and limitation of this approach is discussed together with the conditions for explicitly considering intermetallic interaction parameters u(Ln1Ln2) in more sophisticated chemical models.

The formal 1,3-cycloaddition of 2-diazocyclohexane-1,3-diones 1a–1d to acyclic and cyclic enol ethers in the presence of RhII-catalysts to afford dihydrofurans has been investigated. Reaction with a cis/trans mixture of 1-ethoxyprop-1-ene (13a) yielded the dihydrofuran 14a with a cis/trans ratio of 85 : 15, while that with (Z)-1-ethoxy-3,3,3-trifluoroprop-1-ene (13b) gave the cis-product 14b exclusively. The stereochemical outcome of the reaction is consistent with a concerted rather than stepwise mechanism for cycloaddition. The asymmetric cycloaddition of 2-diazocyclohexane-1,3-dione (1a) or 2-diazodimedone (=2-diazo-5,5-dimethylcyclohexane-1,3-dione; 1b) to furan and dihydrofuran was investigated with a representative selection of chiral, nonracemic RhII catalysts, but no significant enantioselectivity was observed, and the reported enantioselective cycloadditions of these diazo compounds could not be reproduced. The absence of enantioselectivity in the cycloadditions of 2-diazocyclohexane-1,3-diones is tentatively explained in terms of the Hammond postulate. The transition state for the cycloaddition occurs early on the reaction coordinate owing to the high reactivity of the intermediate metallocarbene. An early transition state is associated with low selectivity. In contrast, the transition state for transfer of stabilized metallocarbenes occurs later, and the reactions exhibit higher selectivity.

The introduction of long semirigid spacers between the capping carbon atom of the tripod and the unsymmetrical tridentate binding units provides the novel, extended covalent podand tris-[2-[2-(6-diethylcarbamoylpyridin-2-yl)-1-ethyl-1H-benzoimidazol-5-yl-methoxy]ethyl]methane (L(15)). Reaction of L(15) with lanthanide(III) in acetonitrile produces stable podates [Ln(L(15))](3+) (Ln=La-Lu) in which three tridentate binding units are facially organized. These wrap around the nine-coordinate pseudo-tricapped trigonal-prismatic metal ions. The crystal structure of [La(L(15))](ClO(4))(3) (18, LaC(67)H(82)N(12)O(18)Cl(3), trigonal, R3c, Z=6) reveals the formation of a C(3)-symmetrical triple-helical podate. Two slightly different arrangements of the flexible ethylenoxy parts of the spacer are observed in the solid state in agreement with the formation of two conformational isomers (M:m) in a 4:1 ratio. A qualitative analysis of the aromatic diamagnetic anisotropies affecting the NMR signals of [Ln(L(15))](3+) (Ln=La, Y, Lu) in solution, combined with the quantitative determination of electron-induced relaxation in the paramagnetic complex [Nd(L(15))](3+), demonstrate that the solid state structure is maintained in solution. This leads to a mixture of two triple-helical conformers of similar stabilities and that do not interconvert on the NMR timescale between 243 and 343 K. Particular attention has been given to the structural programming of extended covalent tripods for facially organizing unsymmetrical tridentate binding units around Ln(III). Photophysical measurements show that L(15) efficiently protects the metallic coordination spheres and sensitizes Eu(III) and Tb(III) upon UV irradiation.

Dibenzo-18-crown-6 was chosen as ideal ligand for the complexation of a sodium cation in the aim to allow further coordination of iodide and another oxygen donor ligand in order to generate an asymmetric coordination sphere. The crystal structures obtained with NaI with this ligand and second one with a larger cavity are presented, forming molecular units, and featuring interesting physical properties such as optical birefringence dispersion.

The indenyl roof over the chiral Lewis acid catalyst site of [(indenyl)Ru((S,S)-biphop-F)]+ (see picture) gives rise not only to high enantioselectivities in Diels-Alder reactions between enals and cyclopentadiene but also affects the endo/exo diastereoselectivity. The exo product is formed preferentially even with acrolein.

Benzaldehyde dimethylacetal (1) and 2-aryl-1,3-dioxolanes 5 react with organolithium reagents 2 in the presence of chiral ligands such as sparteine (3), 1-alkoxy-2-aminoethanes, or 1,2-dialkoxyethanes and BF3 to afford monosubstitution products in high yields and in up to 81% enantiomeric excess. The enantioselectivity is strongly influenced by steric effects in the acetal and in the reagent. The highest ee was achieved with 2-(2-isopropyl)-1,3-dioxolane (5c) on treatment with 2-ethylphenyllithium (2i) in the presence of sparteine. The approach was applied to the synthesis of enantioenriched (S)-(−)-neobenodine (17) with 49% ee.

The new chiral bidentate (phosphinoaryl)benzoxazine ligands 2 were applied in asymmetric catalysis. Rhodium and copper complexes catalyzed the hydrosilylation of acetophenone and [4+2] cycloadditions with moderate enantioselectivity. Iridium complexes were used to hyrogenate di-, tri-, and tetrasubstituted alkenes, giving products with moderate to high enantiomer excesses. Enantioselective allylic substitution and Heck reactions catalyzed by [(phosphinoaryl)benzoxazine]palladium complexes occurred with high enantioselectivities. The results were similar to those obtained with the corresponding dihydro(phosphinoaryl)oxazole ligands. Comparison of the structures of (diphenylallyl)(benzoxazine)palladium and (diphenylallyl)(dihydrooxazole)palladium complexes showed that the coordination geometries and the chiral environments of the metal centers are very similar, which explains why the enantioselectivities induced by the two ligand classes are in the same range.

Ba(CF3SO3)2 reacts with the O-donor ligand THF to yield the coordination compound {[Ba(OTf)2(thf)3]2[Ba(OTf)2(thf)2]} (1) (OTf = CF3SO3–). The title compound can be described as a one-dimensional excerpt from the higher-dimensional crystal structure of Ba(CF3SO3)2, stabilized by THF. This example for the concept of formally “cutting out” structural elements from a three-dimensional solid state compound confirms and can be compared to the case of the structural “genealogy tree” of BaI2. This could be an efficient approach for new materials with highly anisotropic properties. Synthese und Kristallstruktur der eindimensionalen polymeren Verbindung {[Ba(OTf)2(thf)3]2[Ba(OTf)2(thf)2]} (OTf = CF3SO3–) – Ausschnitte einer drei-dimensionalen Struktur als Zugang zu neuen Materialien? Ba(CF3SO3)2 reagiert mit dem O-Donorliganden THF zur Koordinationsverbindung {[Ba(OTf)2(thf)3]2[Ba(OTf)2(thf)2]} (1) (OTf = CF3SO3–). Die Titelverbindung kann als eindimensionaler Aussschnitt aus der hoherdimensionalen Kristallstruktur von Ba(CF3SO3)2, stabilisiert durch THF, beschrieben werden. Dieses Beispiel fur das Konzept des „Herausschneidens” von Strukturelementen aus dem dreidimensionalen Festkorper bestatigt den Fall des strukturellen Stammbaums von BaI2 und kann damit verglichen werden. Dies konnte einen neuen Zugang zur Synthese neuer Materialien mit hochst anisotropen Eigenschaften darstellen.

The cobalt(II) complexes prepared with a series of enantiopure ligands (1-3) containing the bis(oxazolinyl)pyridine unit have been studied. The ligands form high spin octahedral complexes as shown by the X-ray crystal structure of the homochiral complex [Co(R,R-1)2](ClO4)2(CH3CN)3. The diastereoselectivity of complex formation has been studied: equimolar mixtures of RR and SS ligands show mixtures of homochiral and heterochiral complexes for 2 and 3, but the phenyl-substituted ligand 1 shows exclusive formation of the heterochiral species. This selectivity is correlated with structural and electronic properties of the complexes.

The stereochemical course of the thermal 2-aza-Cope rearrangement of the optically pure acyl azide (−)-(1S)-5 was investigated by determination of the absolute configuration of the rearrangement product (1R,8S)-9. The reaction proceeds by a sequence of stereospecific steps from 5 to an equilibrating mixture of exo- and endo-isocyanates 6 and 7. The endo-isomer 7 undergoes Cope rearrangement to the putative intermediate 8, which is trapped and characterized as the adduct 9b of butan-1-ol. The absolute configuration of 9b was determined by its reduction to the amide 20, and determination of the X-ray structure of the N-camphanoylamide 21 derived from camphanic acid of known absolute configuration.

CaI2(H2O)2 reacts with O-donor ligands L to yield coordination compounds of the type {[Ca(H2O)2L4]I2}n/, (1: L = CH3COOC2H5, n = 1; 2: L = THF, n = 2). Both compounds feature a coordination number of six around the calcium atom with two water molecules in axial positions and four ligands L in equatorial positions of a tetragonal bipyramid. Due to only a slight variation in the arrangement of the cationic units [Ca(H2O)2L4]2+, hydrogen bonds can be built up between them and the iodide anions in different ways in order to lead to a one-dimensional polymer for 1 and a two-dimensional polymer for 2. Density functional theory calculations provide useful informations on the involved orbitals on the 2-bridging iodide and on the structure of the systems, leading to a small H-I-H angle of 71.2° in 1 compared to a large H-I-H angle of 121.8° in 2.

Epiartemisinin (7) was prepared by the base epimerization of artemisinin (1) and its structure determined by X‐ray analysis. The antimalarial activity of 7 against the chloroquine‐sensitive and resistant strains of Plasmodium berghei and P. yoelii in the mouse was compared with that of the highly effective schizonticide 1 and found to be drastically diminished. It is argued that the mode of action on the intraerythrocytic parasite by 7 is compromised by steric hindrance arising from the α‐disposed Me group. In the initial step, intimate complexation with heme is hindered or biased to favor the formation of a less potent C‐centered radical, the final lethal agent.

Treatment of (aR)‐[1,1′binaphthalene]‐8,8′‐diol ((−)‐1) with hexamethylphosphorous triamide afforded the N,N‐dimethylphosphoramidite (−)‐3 (Scheme 1). The synthesis of the analogous N,N‐diisopropylphosphoramidite 4 failed, however, and afforded the acyclic phosphonamidate (−)‐5. The application of the cyclic phosphoramidite (−)‐3 towards asymmetric catalysis was investigated. The borane reduction of acetophenone (6) to (R)‐1‐phenylethanol (7) in the presence of (−)‐3 proceeded with 96% ee (Scheme 2). The use of (−)‐3 as ligand in several Cu‐catalyzed addition and substitution reactions resulted in enantioselectivities ranging from 0 to 50% (Schemes 3 and 4).

Efficient routes to α-tert-butyl- and α-iso-propyl-ortho-hydroxybenzylamines 1a and 1b are described. Highly enantioenriched 1a and 1b were obtained by resolution of the methoxy derivatives 2 by recrystallization of the salts formed with mandelic acid followed by Lewis acid mediated demethylation. The chiral 1,3-amino alcohol 1a has also been obtained in an asymmetric synthesis with the key step a diastereoselective alkylation of the imine obtained by condensation of o-anisaldehyde with phenyl glycinol. The absolute stereochemistry of these 1,3-aminophenols was determined by CD spectroscopy of the salicylideneamines 12 and by an X-ray structure analysis of the salt formed between (R)-mandelic acid and (S)-α-tert-butyl-ortho-methoxybenzylamine ((S)-2a).

Its information content is infinitely smaller than that of DNA, but its structure (see picture) ressembles the double-stranded helix produced by nature. This self-assembled, configurationally predetermined coordination polymer is built up from enantiopure chiral bipyridine-type ligands and silver ions.

Ease of generation, stablity in solution at ambient temperature, high enantioselectivity in Diels-Alder reactions, efficient catalyst recovery, and large rate differences on variation of the anion are all characteristics of the new Ru Lewis acid [CpRu((S,S)-biphop-F)]+ (biphop-F=(C6F5)2POCH2(Ph)CH2(Ph)OP(C6F5)2). The structure of complex 1 (L=methacrolein, Y=SbF6) provides evidence for a cooperative binding of the dienophile by both the Lewis acid and the anion.

Several aspects of the heterogeneous actions of aqueous and gaseous HCl on the chemical behavior of 3,4‐epoxycyclopentanone (=6‐oxabicyclo[3.1.0]hexan‐3‐one; 1) included in the asymmetric cages of tri‐o‐thymotide (TOT) clathrates belonging to space groups P3₁21 are described, showing specific features strikingly at variance with those observed in liquid solutions. In a first step, the substrate underwent an acid‐promoted allylic isomerization, as already observed in our previous investigations, to give optically active 4‐hydroxycyclopent‐2‐en‐1‐one (2). In a consecutive step, a displacement of the OH group was accomplished by the Cl⁻ anion to afford the corresponding chloro compound 3. Polymorphism was encountered in the preparation of TOT/1 clathrates. Recrystallization of TOT in the pure guest 1 yielded micro‐twinned crystals belonging to the P3₁ space group (host/guest ratio 1 : 1), whereas the expected P3₁21 lattice grew from a mixture of TOT, 1, and MeOH. The structural determination of TOT/1 was carried out by X‐ray diffraction (Fig. 1). Kinetic measurements were achieved that shed light on some striking features of this type of heterogeneous reactions for solid‐liquid and solid‐gas systems. Several reactions of pure clathrate antipodes (+)‐TOT/1 with gaseous HCl were carried out under various conditions; concentration and enantiomer‐excess(ee) determinations of the products 2 and 3 allowed to establish a larger ee for 3, thus demonstrating the influence of the host‐guest diastereomeric association on the progression of the reaction. The correlation of optical activities of the host and products for the global reaction disclosed the sequence (+)‐(M)‐TOT/1→(−)‐2→(−)‐3. A new way for the preparation of 2 was devised. It was further demonstrated that the X‐ray structure analysis of the chiral clathrate (M)‐TOT/(+)‐2 (Fig. 4) associated with chiroptical measurements was an efficient and straightforward method to determine the absolute (+)‐(R)‐configuration of the guest. The enantioselectivity of the TOT clathrate for 2 was established by two different methods which allowed the appraisal of an accurate revised value of the specific rotation of 2. The enclathration of 3 occurred exclusively in the orthorhombic centrosymmetric host lattice Pbca, thus prohibiting the X‐ray structural determination of the guest absolute configuration. The problem of finding a pathway to the intended enantiomer enrichment of 3 was worked out through the action of aqueous HCl on microcrystalline (+)‐TOT/(−)‐(S)‐2 that gave an optically active mixture of unreacted 2 with 3 as sole product. The pure optically active 3 was isolated by subsequent TLC. The resolution of 3 was achieved by GC over a chiral column and its (unknown) specific rotation measured. The absolute configuration of 3 was established by the measurement of the enantiomer purity of the optically active mixture 3 obtained after the total conversion of (−)‐(S)‐2 in the presence of thionyl chloride in Et₂ O, dioxane, and benzene. It was deduced that the (−)‐3 enantiomer had the (S)‐configuration.

Sequential reaction of the tricarbonyl[(?6-phenyl) carbamate]chromium complex 3 with chiral amide bases (see 4 and 5) and electrophiles yielded planar chiral ortho-substituted complexes 6 with up to 70% enantiomeric excess (ee) (Scheme 2, Table 1 and 2). The enantiomer purity could be increased to >90% ee by fractional crystallization. In all but one case the racemate crystallized selectively, leaving the enantiomerically enriched complex in solution. X-Ray crystal-structure analyses of rac-6a and (1R)-6a suggest that this can be ascribed to a more favorable packing of enantiomers of opposite configuration in the solid state than that of the enantiomerically pure solid. Increasing the temperature of the intermediate ortho-lithiated aryl carbamate complex induced an anionic ortho-Fries rearrangement: The 1,3-transposition of the carbamoyl group yielded the ortho-substituted (?6-benzamide)tricarbonylchromium complexes 10 in 65% yield, after exposure to the electrophile (Scheme 6), and the use of a chiral amide base 5 in the deprotonation step afforded the product with an ee of 54%.

The cyclopropenation of diethoxypropyne (1) with methyl diazoacetate in the presence of [Rh₂{(2S)‐mepy}₄] (mepy=methyl 5‐oxopyrrolidine‐2‐carboxylate) proceeds with >95% ee. The resulting cyclopropenecarboxylate 2 underwent stereoselective hydrogenation to the cis‐cyclopropane 3. Hydrolysis of the acetal function of 3 liberated the formyl cyclopropenecarboxylate 4, which was transformed by Wittig reaction with the phosphonate 5 to afford dehydroamino acid 6 as a mixture of (Z)‐ and (E)‐isomers in various proportions. The (Z)‐isomer 6a was hydrolyzed, and the structure and the absolute configuration of the (Z)‐dicarboxylic acid 7a were established by X‐ray crystallography. The cis‐divinylcyclopropane 11 (ee>95%), in turn, was synthesized from 4 via Wittig reaction to afford 8, which was transformed to the aldehyde 10 and subjected to a second Wittig reaction. Thermolysis of 11 afforded (+)‐dictyopterene C′ (12) in quantitative yield.

A series of dinuclear triple- helical complexes of iron(ii) and co- balt(iii) with bis(2-(pyrid-2'-yl)benz- imidazol-5-yl)methane ligands 2 were compared with the analogous mono- nuclear complexes of Fe(ii) and Co(iii) with 2-(pyrid-2'-yl)benzimidazole ligands 1. With the dinucleating ligands 2 only one complex is formed, in contrast to the mononuclear complexes, for which step- wise formation is observed. The crystal structures of fac-(Co( 1a ) 3)(ClO4)3 · EtCN and (Fe2( 2c ) 3)(ClO4)4 ·4 CH 3CN are reported and compared with previ- ously determined triple-helix structures to show that the formation of the helicate does not involve significant distortion of the metal coordination sphere, and that a decrease in metal - nitrogen bond length results in a longer metal - metal distance. Magnetic suscep- tibilities were measured between 243 and 323 K in CD3CN solution for

The surprising answer to the question Are the structural characteristics of the product of the nucleophilic addition to complex 1 those of a cyclohexadienyl complex (2 a) or those of a diene aza-enolate complex (2 b)? is: both. This is indicated by the X-ray structure determination of the complex with R=naphthyl. An unprecedented endo-hydride abstraction concludes the sequence that provides a new route to 1,2-substituted planar chiral [(n6-arene)Cr(CO)3] compounds.

Wie ein Turbinenrad sieht die Struktur des enantiomerenreinen Helicats [Ag6(L2)6]6+1 aus, das als 1⋅(PF6)6-Salz beim Mischen von gelostem AgPF6 und dem Liganden L2 (zwei uber eine Xylylenbrucke verknupfte kondensierte α-Pinen/Bipyridineinheiten) entsteht. Das Helicat hat einen Ausendurchmesser von ca. 3 und einen Innendurchmesser von 0.84 nm und konnte vielleicht fur stereospezifische Erkennungsprozesse genutzt werden.

The ligdnd N,N,N',N'-tetraethylpyridine- 2,6-dicarboxamide (Ly) reacts with trivalent lanthanide ions (Ln"') to give stable mononuclear triplestranded helical complexes [Ln(L9)J3 + (Ln = La to Lu).The crystal and molecular structures of [La(L9),](CI0,), 2.5C2H,CN (8) and [Eu(L9),](Tf0),. 2THF (9) show that the three ligand strands are each meridionally tricoordinated to produce a pseudo-tricapped trigonal prismatic arrangement of the nine donor atoms (six amide 0 and three pyridine N) around Ln"'. The distortions in the La"' coordination sphere of 8 are more significant than for Eu"' in 9, and the photophysical studies on Eu-doped (2 Yn) La, Gd, and Lu complexes confirm a better structural match of L9 for the heavy Ln"' ions. The separation of contact and pseudo-contact contributions to the induced lanthanide paramagnetic NMR shifts in [Ln(L9),13 + shows that the triple-helical structure is maintained in acetonitrile, buta minor structural change relative to that observed in the solid state occurs between Tb"' and Er"' leading to two distinct isostructural series for Ln = La-Tb and Ln = Er-Lu. The origin of this effect together with its consequences for the dynamic helical (P+M) interconversion and stability of [Ln(LY)J3+ in solution are discussed. A detailed investigation of the emission properties of [Ln(L9)J3 + (Ln = Eu, Tb) shows that mixed pyridinecarboxamide ligands can be used to simultaneously optimize the structural and photophysical properties in mononuclear triple-helical lanthanide building blocks.

The [Rh₂(OAc)₄]‐catalyzed decomposition of {[(4‐nitrophenyl)sulfonyl]imino}phenyl‐λ³‐iodane (NsN=IPh) resulted in formal insertions into CH bonds, activated by phenyl or vinyl groups, or by O‐substituents. Scope and limitations of the reaction were investigated. Yields of up to 84% were achieved in the most favorable cases. Yields were enhanced by electron‐releasing substituents and decreased by steric hindrance. Aziridination competed with allylic insertion with olefinic substrates. The insertion reaction proceeded with retention of configuration. With chiral RhII catalysts, a modest asymmetric induction was observed. A mechanism involving direct insertion by a Rh‐complexed nitrene into the CH bond is proposed.

The title compounds 4 are obtained by photolysis of simple N-alkylpyridinium salts in H2O or alcohol. On reaction with [Fe2(CO)9] in THF, 4 gives bicyclic tricarbonyliron complexes 13a–d, which on oxidative decomplexation with ceric ammonium nitrate afford cis-fused cyclopenteno-β-lactams 15a–d.

The [Rh2(OAc)4]-catalyzed addition of methyl diazoacetate to N-benzylideneaniline (1a) afforded the imine cis-2 in 35% yield. Under catalysis by chiral RhII catalysts, however, only racemic 1a was produced, and the yield was low. In the presence of dimethyl maleate, aziridine formation was suppressed, and an intermediate ylide 6 was trapped as cycloadduct 7. No aziridines were obtained, however, from 1b, 1c, and 3. The iminium salt 8 reacted with (trimethylsilyl)diazomethane in the absence of [Rh2(OAc)4] via dipolar cycloaddition followed by extrusion of N2 to 10.

The absolute configuration of a series of naturally occurring and semi-synthetic halogenated furanones is proposed on the basis of chemical interconversions and X-ray and CD analyses. The CD analyses clearly reveal that the presence of the allylic O-atom has a strong influence in determining the sign and intensity of the low energy ππ* transition.

Two pairs of enantiomerically pure cis-fused cyclopenteno-1,2,4-trioxanes (7, ent-7 and 8, ent-8) are prepared (Schemes 1-3). Their identities are established by dye-sensitized photo-oxygenation of ent-7 and 8, ent-8 to the allylichydroperxides, reduction to the corresponding alcohols, and conversion to the (1S)-camphanates (Scheme 4), the structures of which are determined by X-ray analysis. The dynamic properties of ent-7 are investigated by NMR spectroscopy and PM3 calculations. Evidence for an easily accessible twist-boat conformation is obtained. The in vitro and in vivo antimalarial activities of 7, ent-7,8, and ent-8 as well as those of the racemic mixtures are evaluated against Plasmodium falciparum, P. berghei, and P. yoelii. No correlation is observed between configuration and activity. Racemates and pure enantiomers have commensurate activities. The mode of action on the intraerythrocytic parasite is rationalized in terms of close docking by the twist-boat conformer of the trioxane on the surface of a molecule of heme, single-electron transfer to the O--O d* orbital, and scission to the acetal radical which then irreversibly isomerizes to a C-centered radical, the ultimate lethal agent (Scheme 5).

Treatment of the uracil (I) with the acrylates (II) followed by cyclization and chlorination provides an efficient approach to 2,4,8-trichloropyridopyrimidines.