Samarium diiodide-induced intramolecular pinacol coupling of dinitrones: synthesis of cyclic cis-vicinal diamines.

Pinacol coupling of alkyl dinitrones mediated by SmI2 was achieved in the presence of a proton source allowing the synthesis of cyclic vicinal diamines with good cis-selectivity.

Preparation of a novel diphosphine-palladium macrocyclic complex possessing a molecular recognition site. Oxidative addition studies.

A disphosphine-palladium(0) complex capable of recognising barbiturates has been prepared. Oxidative addition studies with a barbitiurate:aryl iodide conjugate provided new Pd(ii) complexes where the positioning of the Pd-bound aryl group is controlled by the molecular recognition event.

Radical addition of nitrones to acrylates mediated by SmI2: asymmetric synthesis of gamma-amino acids employing carbohydrate-based chiral auxiliaries.

Alkyl nitrones possessing N-substituted sugars as chiral auxiliaries were found to effectively undergo an SmI(2)-mediated radical addition to n-butyl acrylate affording gamma-amino acid derivatives with high diastereomeric control.

Total Synthesis of (R)-Dihydroactinidiolide and (R)-Actinidiolide Using Asymmetric Catalytic Hetero-Diels-Alder Methodology.

The total synthesis of the naturally occurring bicyclic lactones (R)-dihydroactinidiolide and (R)-actinidiolide is presented. The key step in the syntheses is the copper(II)-bisoxazoline-catalyzed hetero-Diels-Alder reaction of a cyclic diene with ethyl glyoxylate giving the hetero-Diels-Alder product in high yield and with very high regio-, diastereo-, and enantioselectivity. The total syntheses proceed via an intermediate, which also has the potential for a series of other natural products. The structure of the key intermediate is confirmed by X-ray analysis.

Catalytic Approach for the Formation of Optically Active Allyl alpha-Amino Acids by Addition of Allylic Metal Compounds to alpha-Imino Esters.

A new catalytic enantioselective approach for the formation of allyl alpha-amino acid derivatives by reaction of N-tosyl alpha-imino esters with allyl stannanes and silanes catalyzed by chiral copper(I) complexes has been developed. A series of different BINAP and phosphine-oxazoline (P,N) ligands have, in combination with various Lewis acids, been tested as chiral catalysts for allylation of N-tosyl alpha-imino esters. It has been found that both type of ligands, in combination with copper(I) salts, give highly valuable unsaturated alpha-amino acid derivatives. The reaction has been investigated for different allyl stannanes and silanes, and it has been found that tri-n-butyl allyl stannane gives the best results of the simple allyl compounds tested, leading to gamma,delta-unsaturated alpha-amino acid derivatives in up to 94% yield and with up to 83% ee, which can be improved to be >95% ee by recrystallization. The reaction has also been investigated using different acyclic and cyclic allyl stannanes leading to various types of unsaturated alpha-amino acid derivatives in very high yield (up to 95%) and with up to 98% ee. The stereochemistry and absolute configurations of the allyl alpha-amino acid derivatives have been determined by X-ray analysis, and it is suggested that the reaction takes place as an ene-like reaction.

Chiral CO(2)-Synthons via Catalytic Asymmetric Hetero-Diels-Alder Reactions of Ketomalonate and Dienes.

A catalytic enantioselective approach for the formation of chiral CO(2)-synthons is presented. The described methodology is based on the reaction of dienes with diethyl ketomalonate using C(2)-symmetric bisoxazolines as the chiral ligands and copper(II) and zinc(II) as the Lewis acids. For cyclic dienes the reaction proceeds in good yield and with up to 93% ee for 1,3-cyclohexadiene, while for cyclopentadiene the reaction also proceeds well at low temperature, but increasing the temperature leads to a retro-Diels-Alder reaction. The reaction has been studied under different conditions and for various dienes, and it has been found that for activated dienes both the hetero-Diels-Alder and Mukaiyama aldol products are isolated. The compound formed by the enantioselective hetero-Diels-Alder reaction of 1,3-cyclohexadiene with ketomalonate has been converted to both the CO(2)-synthon formed in principle from the [2+4] cycloaddition reaction of CO(2) and 1,3-cyclohexadiene, and attractive optically active 1,4-disubstituted cyclohexene diols. The absolute configuration of the hetero-Diels-Alder adduct has been assigned on the basis of the structure of (1S)-camphanic ester of a 1,4-disubstituted cyclohexene diol which gave suitable crystals for X-ray analysis. The reactions have also been analyzed from a theoretical point of view. First, the [2+4] cycloaddition reaction of CO(2) with 1,3-cyclohexadiene has been investigated, and then the relative stability of the two major isomers of bidentate ketomalonate coordinated to a copper(II) or zinc(II) Lewis acid dication was investigated applying density functional theory calculations. Finally, the energetics of the [2+4] hetero-Diels-Alder addition mechanisms typical of the reaction with normal dienes catalyzed by C(2)-symmetric bisoxazoline-zinc(II) complexes using semiempirical calculations are presented.

Improvement of TADDOLate-TiCl(2)-Catalyzed 1,3-Dipolar Nitrone Cycloaddition Reactions by Substitution of the Oxazolidinone Auxiliary of the Alkene with Succinimide.

A significant improvement of metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions of acyclic nitrones with alpha,beta-unsaturated carbonyl compounds is described using succinimide as a new auxiliary for the alpha,beta-unsaturated carbonyl moiety. In the absence of a catalyst, N-crotonoylsuccinimide reacts with C,N-diphenylnitrone to give the endo-isoxazolidine, whereas in the presence of 10 mol % TiCl(2)(i-PrO)(2) the exo-product is obtained. Four different TiCl(2)-TADDOLate complexes have been tested as catalysts for the 1,3-dipolar cycloaddition reactions, and the most successful catalyst was applied (5 mol %) in a series of reactions between two different alkenoylsuccinimides and three different nitrones. The crude products containing an N-acylsuccinimide moiety were converted directly into the corresponding carboxamides upon treatment with hydrazine. The 1,3-dipolar cycloaddition reactions proceed with a high degree of exo-selectivity, often >90% de, which is an improvement compared with previous experiments performed using the oxazolidinone auxiliary for the alkenoyl moiety. Furthermore, the enantioselectivities are also improved compared with previous work, and ee up to 73% is obtained, which is the highest ee found for these metal-catalyzed exo-selective 1,3-dipolar cycloaddition reactions. The ee can be improved to >90% by recrystallization. The absolute structure of the 1,3-dipolar cycloaddition adduct is determined on the basis of the X-ray crystal structure of a compound with a known configuration. On the basis of this knowledge of the absolute structure of the product the mechanism of the reaction is briefly discussed.

Catalytic Enantioselective Aza Diels-Alder Reactions of Imino Dienophiles.

1 mol% of catalyst is sufficient: The hetero Diels-Alder reaction of α-imino esters 1 with activated conjugated dienes 2 (R=H, Me) needs only 1 mol% of a 2,2'-bis(diarylphosphanyl)-1,1'-binaphthyl (BINAP) copper(I) complex as the catalyst to generate the adducts 3 in good yields and with enantioselectivities up to 96%. The reaction can also be carried out on gram scale! Tos=H3 CC6 H4 SO2 ; TMS=Me3 Si.

Solid-state (14)N MAS NMR of ammonium ions as a spy to structural insights for ammonium salts.

The high resolution offered by magic-angle spinning (MAS), when compared to the static condition in solid-state NMR of powders, has been used to full advantage in a (14)N MAS NMR study of some ammonium salts: CH(3)NH(3)Cl, (NH(4))(2)(COO)(2) x H(2)O, (CH(3))(3)(C(6)H(5)CH(2))NCl, (CH(3))(3)(C(6)H(5))NI, [(n-C(4)H(9))(4)N](2)Mo(2)O(7), (NH(4))(2)HPO(4), and NH(4)H(2)PO(4). It is shown that the high-quality (14)N MAS NMR spectra, which can be obtained for these salts, allow determination of the (14)N quadrupole coupling parameters, i.e. C(Q) (the quadrupole coupling constant) and eta(Q) (the asymmetry parameter), with very high precision. In particular, it is shown that precise C(Q), eta(Q) parameters can be determined for at least two different (14)N sites in case the individual spinning-sideband (ssb) intensities arise from a single manifold of ssbs, i.e. the ssbs for the two sites cannot be resolved. This feature of (14)N MAS NMR, which is the first demonstration for manifolds of ssb in MAS NMR without the potential information from a central transition, becomes especially useful at the slow spinning frequencies (nu(r) = 1000-1500 Hz) applied to some of the ammonium salts studied here. The detection of the number of sites has been confirmed by the corresponding crystal structures determined from single-crystal X-ray diffraction (XRD), either in this work for the unknown structure of benzyl trimethylammonium chloride or from reports in the literature. The magnitudes of the (14)N quadrupole coupling constants for the ammonium salts studied here are in the range from C(Q) approximately 20 kHz to 1 MHz while the asymmetry parameters span the full range 0 < or = eta(Q) < or = 1. Clearly, the (14)N quadrupole coupling parameters (C(Q), eta(Q)) for ammonium ions appear highly sensitive toward crystal structure and therefore appreciably more informative for the characterization of ammonium salts in comparison to the isotropic (14)N (or (15)N) chemical shifts.

Enantioselective Friedel-Crafts type addition of indoles to nitro-olefins using a chiral hydrogen-bonding catalyst--synthesis of optically active tetrahydro-beta-carbolines.

The enantioselective Friedel-Crafts addition of indoles to nitro-olefins using chiral hydrogen-bonding bis-sulfonamides as the catalysts has been developed. The reactions, in the presence of only 2 mol% catalyst, generally proceed in high yields and with enantioselectivities up to 64% ee, and the enantiomeric excess can be improved to >98% ee by recrystallization. Various synthetic transformations of the Friedel-Crafts adducts are demonstrated: the nitro group can easily be reduced to the corresponding amine and the product obtained can undergo a stereocontrolled Pictet-Spengler cyclization to give, for example, enantiopure tetrahydro-beta-carbolines. The X-ray structure of the chiral bis-sulfonamides has been determined and based on these structures the mechanism for the stereoselectivity in the reaction is discussed.

New amine-templated zinc phosphates with a temperature-induced increase of structural dimensionality.

Three new amine-templated zinc phosphates, [C4N2H14][Zn(HPO4)2].H2O, AU-I, [C4N2H14][Zn2(H(0.5)PO4)2(H2PO4)], AU-II, and [C4N2H14][Zn5(H2O)(PO4)4], AU-III, are prepared by hydrothermal synthesis using an organic amine, N,N'-dimethylethylendiamine CH3NHCH2CH2NHCH3, as structure-directing agent. The three materials are prepared from the same reaction mixture, 1Zn(CH3CO2)2:3.05H3PO4:2.25CH3NHCH2CH2NHCH3:138H2O (pH = 5.1), AU-I at RT, AU-II at 60 degrees C, and AU-III at 170 degrees C. The materials are built from corner-sharing ZnO4 and PO4 tetrahedra forming chains, layers, or framework structures for AU-I to III, respectively, and are linked together by hydrogen bonds via the diprotonated amine ions. The complete hydrogen-bond scheme is resolved for these new compounds and reveals some interesting phenomena, for example, a hydrogen shared between two phosphate groups in AU-II, thereby forming H(0.5)PO4 groups. Furthermore, the water molecules are different; that is, in AU-I they act as hydrogen-bond donor and acceptor, whereas they act as ligand in AU-III with coordination to Zn. The structures of the compounds are determined by single-crystal X-ray diffraction analysis. AU-I, [C4N2H14][Zn(HPO4)2].H2O, crystallizes in the triclinic space group P-1, a = 8.215(2), b = 8.810(3), c = 8.861(3) A, alpha = 88.001(4) degrees , beta = 89.818(5) degrees , and gamma = 89.773(5) degrees , Z = 2. AU-II, [C4N2H14][Zn2(H(0.5)PO4)2(H2PO4)], is monoclinic, P2/n, a = 11.7877(4), b = 5.2093(2), c = 12.2031(4) A, beta = 98.198(1) degrees , Z = 2. AU-III, [C4N2H14][Zn5(H2O)(PO4)4], crystallizes in the orthorhombic space group Pna2(1) with lattice parameters, a = 20.723(2), b = 5.2095(6), c = 17.874(2) A, Z = 4. The phase stability investigated by systematic hydrothermal synthesis is presented, and the materials are further characterized by 31P solid-state MAS NMR, for example, by determination of 31P chemical shift anisotropies for AU-III, while the thermal behavior is investigated by thermogravimetry (TG).

Two new cobalt-zinc orthophosphate monohydrates: hydrothermal synthesis, crystal structures and thermal investigation.

Two new cobalt zinc orthophosphate hydrates with similar chemical formula, (CoxZn(1-x))3(PO4)2.H2O, but different composition and structure, have been prepared by systematic hydrothermal synthesis from the system nCo(CH3COO)2 : (1 -n)Zn(CH(3)COO)2 : 3.5H3PO4 : 2.1(CH3)2NH(CH2)3NH2:144H2O (0

Catalytic and enantioselective aza-ene and hetero-Diels-Alder reactions of alkenes and dienes with azodicarboxylates.

Lewis acids such as Cu(OTf)(2), Zn(OTf)(2), Yb(OTf)(3) and Nd(OTf)(3) catalyze the aza-ene reaction of alkenes with azodicarboxylates, giving the allylic amination adducts. The use of bis(2,2,2-trichloroethyl)azodicarboxylate as the amination reagent and Cu(OTf)(2) and Yb(OTf)(3) as the catalysts gave the aza-ene reaction of different alkenes, leading to the corresponding allyl amines in high yields. Chiral copper complexes prepared from Cu(OTf)(2) and chiral bisoxazoline ligands were found to catalyze the enantioselective aza-ene reaction of azodicarboxylates with alkenes and the hetero-Diels-Alder reaction with cyclopentadiene, giving the corresponding aza-ene- and hetero-Diels-Alder adducts, respectively, in good yields and moderate enantioselectivities.

Self-assembly of the octanuclear cluster [Cu8(OH)10(NH2(CH2)2CH3)12]6+ and the one-dimensional N-propylcarbamate-linked coordination polymer {[Cu(O2CNH(CH2)2CH3)(NH2(CH2)2CH3)3](ClO4)}n.

The reaction of Cu(ClO4)2.6-H2O and n-propylamine in methanol gives two high-nuclearity products of well-defined compositions. At amine concentrations greater than seven equivalents compared to copper ion concentration, the system fixes carbon dioxide from air to form the one-dimensional carbamate-bridged coordination polymer, {[Cu(mu2-O,O'-O2CNH(CH2)2CH3)(NH2(CH2)2CH3)3](ClO4)}n ({1-ClO4}n). Lower relative amine concentrations lead to the self-assembly of an octanuclear copper-amine-hydroxide cluster [Cu8(OH)10(NH2(CH2)2CH3)12]6+ (2). Both compounds exhibit unique structures: {1-ClO4}n is the first mu2-O,O'-mono-N-alkylcarbamate-linked coordination polymer and 2 is the largest copper-hydroxide-monodentate amine cluster identified to date. The crystal structures indicate that the size of the n-propyl group is probably crucial for directing the formation of these compounds. Magnetic susceptibility studies indicate very weak antiferromagnetic coupling for 1. The octanuclear cluster 2 displays slightly stronger net antiferromagnetic coupling, despite the presence of a number of Cu-O(H)-Cu angles below the value of about 97 degrees that would normally be expected to yield ferromagnetic coupling.

Organocatalytic asymmetric conjugate addition of nitroalkanes to alpha,beta-unsaturated enones using novel imidazoline catalysts.

A new catalytic enantioselective conjugate addition of nitroalkanes to acyclic alpha,beta-unsaturated enones catalyzed by novel organic catalysts has been developed. A series of chiral amines has been tested as catalysts for the addition of 2-nitropropane to benzylideneacetone, and it is found that a novel imidazoline catalyst, prepared from phenylalanine, can catalyze a highly enantioselective 1,4-addition reaction. The reaction of various acyclic and cyclic nitroalkanes was found to proceed well with enantioselectivities up to 86% ee, and enantiopure products can be obtained by recrystallization. The potential of the reaction is documented by the reaction of a series of substituted alpha,beta-unsaturated enones with different nitroalkanes. Furthermore, the synthetic applicability of the reaction is demonstrated by the formation of optically active functionalized pyrrolines and pyrrolidines by reductive amination of the products. On the basis of the absolute configuration of the conjugate addition products, the mechanism for the reaction is discussed and a transition state proposed.

On the intermediates in chiral bis(oxazoline)copper(II)-catalyzed enantioselective reactions--experimental and theoretical investigations.

The intermediates in the chiral bis(oxazoline)copper(II)-catalyzed reactions have been investigated by means of experimental and theoretical investigations. It is shown that the absolute configuration of the hetero-Diels-Alder adduct obtained from the reaction of ethyl glyoxylate with 1,3-cyclohexadiene in the presence of the chiral bis(phenyloxazoline)copper(II) is dependent on the solvent. In this case, a linear relationship between the enantiomeric excess (ee) and the dielectric constant of the solvent was observed. However, the enantiomeric excess for the adduct obtained with the chiral bis(tert-butyloxazoline)copper(II) complex is independent of the solvent. The addition of different coordinating solvents to the chiral catalysts was investigated and no effect on the enantioselectivity of the reaction was observed. A series of chiral bis(tert-butyloxazoline)-, bis(phenyloxazoline)-, and bis(indaneoxazoline)copper(II) complexes has been prepared and characterized by X-ray analysis, and the similarity between the structures is discussed. For comparison, two related chiral bis(tert-butyloxazoline)- and bis(phenyloxazoline)zinc(II) complexes were also prepared and characterized. A series of chiral bis(oxazoline)copper(II)-substrate (the substrate being glyoxal or methyl glyoxylate) complexes was investigated by means of ab initio calculations. Calculation of the total energy of the optimized structure of 17-, 19-, and 21-electron bis(oxazoline)copper(II)-substrate complexes give the 17-electron complex as the most stable and the most reactive complex, while the 21-electron complex is less stable and also much less reactive. The optimized structures of both the 17-electron bis(tert-butyloxazoline)- and bis(phenyloxazoline)copper(II)-substrate complexes show that the plane of the substrate molecule is twisted by approximately 40-45 degrees out of the bis(oxazoline)copper(II) plane, in agreement with the X-ray structures. On the basis of the experimental results, X-ray structures, and ab initio calculations, the structure of the intermediate(s) and reactivity of the chiral bis(oxazoline)copper(II)-substrate complexes are discussed.