Sambucinic Acid,a New Metabolite of Fusarium sambacinum. 45th communication on verrucarins and roridins

Sambucinic acid (5), a C₁₅-trichothecene with a modified strure, has been isolated from cultures of Fusarium sambucinum. The structure is established by spectroscopic data and X-ray diffraction analysis. A hypothetical biogenetic pathway is proposed.     

Enantioselective Allylic Substitution Catalyzed by Chiral [Bis(dihydrooxazole)]palladium Complexes: Catalyst structure and possible mechanism of enantioselection

Allylpalladium complexes with chiral bis(dihydrooxazole) ligands were studied as catalysts for the enantioselective allylic substitution reaction of rac-1,3-diphenylprop-2-enyl acetate (rac- 5 ) with the anion of dimethyl malonate (Scheme 1). Using enantiomerically pure (S,E)-1-(4-tolyl)-3-phenylprop-2-enyl acatete ((S)- 25 ) as substrate, the reaction was shown to proceed by a clean ‘syn’ displacement of acetate by dimethyl malonate (Scheme 6). The [Pd¹¹(η³-allyl)] complex 18 and the analogous [Pd(η³-1,3-diphenylallyl)] complex 20 , both containing the same bis(dihydrooxazole) ligand, were characterized by X-ray structure analysis and by NMR spectroscopy in solution. The structural data reveal that steric interactions of the allyl system with the chiral ligand result in selective electronic activation of one of the allylic termini. The higher reactivity of one allylic terminus toward nucleophilic attack is reflected in a significantly longer Pd? C bond and a shift of the corresponding ¹³C-NMR resonance to higher frequency.     

Synthesis and Complexation of 1,2-Bis[(monoaza[15]crown-5)-N-yl]glyoxime. Crystal Structure of (1,2-Bis[(monoaza[15]crown-5)-N-yl]glyoximato)palladium(II)

A new vicinal dioxime ligand with two crown-ether groups, 1,2-bis[(monoaza[15]crown-5)-N-Yl]-glyoxime(LH₂), has been prepared from cyanogen di-N-oxide and monoaza[15]crown-5. Ni(II), Pd(II), and Pt(IV) complexes of LH₂ with or without alkali-metal ions bound to macrocyclic groups have been isolated. The high affinity of [Pd(LH)₂] and [Ni(LH)₂] for the K⁺ ion is observed in solvent extraction experiments. A single-crystal X-ray structure confirms the postulated geometry of [Pd(LH)₂]- The Pd-atom of the centro-symmetric molecule has square-planar PdN₄ coordination where Pd–N distances range from 1.978(3) to 1.970(3) Å. The N–Pd–N intraligand angle is 79.9(1)^°.     

Metal complexes of macrocyclic ligands. Part XXIV. Binuclear complexes with tetraazamacrocycle-N,N′,N″,N‴-tetraacetic acids

The three ligands H₄dota, H₄teta, and H₄heta give binuclear complexes with Cu²⁺ and Ni²⁺, the spectral properties of which have been studied. The structures of Cu₂(dota)·5H₂O and Cu₂(teta)·6H₂O have been established by X-ray diffraction analysis.     

C2-Symmetrical Pyrrolidine Derivatives Chiral Auxiliaries in Radical Chemistry

Fumaramides 3b and 3c bearing the C₂-symmetrical pyrrolidine moieties (2R,5R)-2,5-bis(methoxymethyl)pyrrolidine ( 2b ) or 1,3:4,6-di-O-benzylidene-2,5-dideoxy-2,5-imino-L -idit ( 2c ), respectively, as a chiral auxiliary lead to high diastereoselectivities in radical reactions (‘tin method’;Scheme 1). Removal of the chiral auxiliaries affords the corresponding alkylated fumaric acids Scheme 2. Single-crystal X-ray structures of 3b and 3c support arguments that lead to the model of 1,4-stereoinduction.     

Mehrkernige Kobaltkomplexe. II. Herstellung und Struktur von [(tren) (NH3)Co(O2)Co(NH3) (tren)](SCN)4 · 2H2O

Polynuclear Cobalt Complexes. II. Preparation and Structure of [(tren) (NH₃)Co(O₂)Co(NH₃) (tren)](SCN)₄ · 2H₂O The title compound is obtained on oxygenation of [Co(tren)(H₂O)₂]²⁺ in 6M aqueous ammonia or by ligand exchange starting from [(NH₃)₅Co(O₂)Co(NH₃)₅]-(NO₃)₄. An X-ray structure determination was made. The substance forms monoclinic crystals, space group P2₁/c, lattice constants a=10,135, b=8,473, c=19,484 Å, β=108,58°, with two formula units in the cell. The final R is 0,066. The binuclear cation has a center of symmetry, so the Co? O? O? Co unit is planar; the Co? O? O angle is 111,5°. The tertiary nitrogen atoms of both chelate groups are cis to the O₂ bridge, as found in doubly bridged [(tren)Co(O₂,OH)Co(tren)](ClO₄)₃ · 3H₂O. On acidification in solution, the singly bridged cation [(tren) (NH₃)CoO₂Co(NH₃)(tren)]⁴⁺ (a) loses the bound O₂ completely. But unlike the doubly bridged cation b , the rate of dissociation of a is independent of pH (Fig. 5). At higher pH (8–10) bridging a→b (Fig. 2) occurs. Both reactions must have the same rate determining step, the first order rate constants being of the order of 2 · 10^?3 s^?1 (25°, 0,35M KCl).     

Mehrkernige Kobaltkomplexe. III. Über meso-[(en)2Co(OH)2Co(en)2] (NO3)4

Polynuclear Cobalt Complexes. III. On meso-[(en)₂Co(OH)₂Co(en)₂] (NO₃)₄ The structure of the title compound has been determined by X-ray analysis and refined to R = 0,060. The crystals are monoclinic, space group very probably C2/m, with cell dimensions a = 16,113(3), b = 10,946(2), c = 7,193(2) Å, β = 113,22(2)° and Z = 2. The configuration of the cation is ΔΛ IR. and UV./VIS. spectroscopic data are given.     

Morse-type index theory for flows and periodic solutions for Hamiltonian Equations

An index theory for flows is presented which extends the classical Morse theory for gradient flows on compact manifolds. The theory is used to prove a Morse-type existence statement for periodic solutions of a time-dependent (periodic in time) and asymptotically linear Hamiltonian equation.