MnI/AgI Relay Catalysis: Traceless Diazo‐Assisted C(sp2)–H/C(sp3)–H Coupling to β‐(Hetero)Aryl/Alkenyl Ketones

An unprecedented Mn^I/Ag^I‐relay‐catalyzed C(sp²)?H/C(sp³)?H coupling of (vinyl)arenes with α‐diazoketones is reported, wherein the diazo group was exploited as a traceless auxiliary for control of regioselectivity. Challenging β‐(hetero)aryl/alkenyl ketones were obtained through this operationally simple approach. The cascade process merges denitrogenation, carbene rearrangement, C?H activation, and hydroarylation/hydroalkenylation. The robustness of this method was demonstrated at preparative scale and applied to late‐stage diversification of natural products.     

Study of terbium(III)–dextran and terbium(III)–α-methyl glucoside interactions

The interaction of dextran with terbium(III) was studied in aqueous solution, pH 3.0–6.6, by fluorescence and optical rotatory dispersion. The polysaccharide enhances Tb(III) fluorescence intensity when the system is excited at the 290-nm hypersensitive transition (⁷F₆ → ⁵H₄). The dextran rotatory power is decreased in the presence of the metal ion. The results indicate that a 38% maximum of the polymer repeat units are coordinated. Complex formation occurs with displacement of water from the cation coordination sphere by hydroxyl groups at the second and third carbon atoms of the pyranoside ring. As the pH increases, a more asymmetric complex is formed. The α-methyl glucoside, low molecular weight dextran analogue, interacts with Tb(III) less strongly than dextran. Fluorimetric titrations indicated that the order of binding ability to polysaccharide is Tb(III) > Al(III) > Ca (II). © 1993 John Wiley & Sons, Inc.     

σ–π Continuum in Indole–Palladium(II) Complexes

The intrinsic features of (hetero‐arene)–metal interactions have been elusive mainly because the systematic structure analysis of non‐anchored hetero‐arene–metal complexes has been hampered by their labile nature. We report successful isolation and systematic structure analysis of a series of non‐anchored indole–palladium(II) complexes. It was revealed that there is a σ–π continuum for the indole–metal interaction, while it has been thought that the dominant coordination mode of indole to a metal center is the Wheland‐intermediate‐type σ‐mode in light of the seemingly strong electron‐donating ability of indole. Several factors which affect the σ‐ or π‐character of indole–metal interactions are discussed.     

η-Pentamethylcyclopentadienylruthenium(II) complexes containing η-coordinated α-amino acids

Reaction of [Cp* RuCl₂]₂ with -alanine ( -alaH) in methanol at room temperature in the presence of NaOMe yields the complex Na[Cp* RuCl( -ala)] (1), which contains a five-membered N,O-coordinated chelate ring. The analogous complex Na[Cp* RuCl( -phe)] (2) is obtained under similar conditions but at 0°C in 90% yield. At temperatures above 20°C both 2 and the η⁶-coordinated complex [Cp* Ru( -pheH)]Cl (4) are obtained, with the proportion of the latter increasing with temperature. Compound 4 is obtained in 88% yield by refluxing [Cp* RuCl₂]₂ and -phenylalanine ( -pheH) in CH₃OH/CH₃ONa followed by separation from 2. The analogous ruthenium(II) sandwich complexes 5–10 were obtained from -tyrosine and -tryptophane and various derivatives. [Cp* Ru( -met)] (3), prepared by the reaction of [Cp* RuCl₂]₂ with -methionine ( -metH) in CH₃OH/CH₃ONa, displays N,O,S-coordination.     

The structure–activity relationship of some hexacoordinated dimethyltin(IV) complexes of fluorinated β‐diketone/β‐diketones and sterically congested heterocyclic β‐diketones

The study was focused on the structure–activity relationship of some newly synthesized hexacoordinated dimethyltin(IV) complexes of fluorinated β‐diketone/β‐diketones and sterically congested heterocyclic β‐diketones. These complexes were screened for their antibacterial activity against a Gram‐negative bacterium (Pseudomonas aeruginosa) and Gram‐positive bacteria (Streptomyces griseus, Staphylococcus aureus, Bacillus subtilis) and the results were compared with those of a standard antibacterial drug. Some of the complexes were also screened for their antifungal activity against various fungi (Aspergillus niger, A. flavus, Trichoderma viride, Fusarium oxysporum) and were found to be active. These new hexacoordinated complexes of dimethyltin(IV) were generated by reactions of dimethyltin(IV) dichloride and sodium salts of fluorinated β‐diketone/β‐diketones and sterically congested heterocyclic β‐diketones in 1:1:1 molar ratio in refluxing dry benzene. Plausible structures of these complexes were suggested with the aid of physicochemical and spectroscopic studies. ¹¹⁹Sn NMR spectral data revealed the presence of a hexacoordinated tin centre in these dimethyltin(IV) complexes. Copyright © 2015 John Wiley & Sons, Ltd.     

Circular dichroism of copoly(γ-stearyl-L-glutamate–γ-methyl-L-glutamate)

Copoly(γ-stearly-L -glutamate-γ-methyl-L -glutamate)s with various compositions were synthesized by the ester exchange reaction of poly(γ-methyl-L -glutamate). Circular dichroism studies were carried out for solution and solid film as a function of the degree of stearylation and temperature. The slight and gradual temperature dependence of molecular ellipticity was observed for solution of all the copolyglutamates studied here and for the solid film of the copolyglutamate with the degree of stearylation of 16%, indicative of no reversal in the helix sense. However the remarkable change in negative molecular ellipticity with temperature was detected for the solid film of the copolyglutamate with a low degree of stearylation, e.g., 52%, whereas the drastic change in molecular ellipticity from a negative to positive value appeared for that with a higher degree of stearylation. This is discussed in terms of the reversal in the helix sense from a right- to left-handed α helix with the increase of temperature occurring at the melting temperature of the ordered side chain region.     

K21–δNa2+δIn39 (δ = 2.8): A Cluster-Replacement Clathrate-II Structure with an Alkali Metal M136-Network

K_21–δNa_2+δIn₃₉ with δ = 2.82 was synthesized (melted at 973 K, annealed at 623 K) from the elements in sealed niobium ampoules. The compound forms prismatic crystals with silver metallic lustre and is unstable in air and moisture. The crystal structure of K_21–δNa_2+δIn₃₉ (orthorhombic; space group Pnma, No. 62; a = 17.844(5) Å, b = 17.192(3) Å, c = 25.078(7) Å; Z = 4; Pearson code oP248; δ = 2.82, obtained from the structure refinement) contains eight empty In icosahedra of two types, A (12 exo-bonds) and B (7 exobonds), and four open In₁₅ clusters (15 exo-bonds). The latter are centered by K atoms and belong to C units, which are defined as [K(Na₂M₃In₁₅)] heteroatomic clusters (M = K + Na). The spatial distribution of the In icosahedra A, B and heteroatomic clusters C is that of the atoms in the cubic Laves phase MgCu₂: MgCu₂ ? [K(Na₂M₃In₁₅)][In]₂. All the In_n clusters are interconnected by exo-bonds forming a covalent three-dimensional framework (d(In? In) = 2.832 to 3.301 Å). The remaining alkali metal atoms build up a three-dimensional M₁₃₆ network of the clathrate-II type with (16 + 8) cages, which envelopes the In icosahedra and [K(Na₂M₃In₁₅)] clusters. This structure can be described as a cluster-replacement derivative of the clathrate-II structure: (H₂S)₁₆(CCl₄)₈ · (H₂O)₁₃₆ ? [In]₁₆[K(M₅In₁₅)]₈M₁₃₆, and is one member of a novel hierarchical structure family, based upon cluster-replacement. The bonding as well as the structural relationships to other phases are discussed.     

Oxidation of Tricarbonyl (η1 η2-but-3-en-1-yl)iron(0)and Tricarbonyl (η3-allyl)iron(0) Anion Complexes with Dioxygen

The addition of reactive carbanions to tricarbonyl(η⁴-1,3-diene)iron(0) complexes proceeded at ?78 °C to give putative tricarbonyl(η¹,η²-but-3-en-1-y1)iron(0) anion complexes and at 25 °C to produce postulated tricarbonyl(η³-allyl)iron(O) anion complexes; trapping of reactive intermediates with dioxygen produced γ,δ-unsaturated acids and allylic alcohols, respectively.     

N,N′‐Dioxide/Nickel(II)‐Catalyzed Asymmetric Inverse‐Electron‐Demand Hetero‐Diels–Alder Reaction of β,γ‐Unsaturated α‐Ketoesters with Enecarbamates

N,N′‐Dioxide/nickel(II) complexes have been developed to catalyze the inverse‐electron‐demand hetero‐Diels–Alder reaction of β,γ‐unsaturated α‐ketoesters with acyclic enecarbamates. After detailed screening of the reaction parameters, mild optimized reaction conditions were established, affording 3,4‐dihydro‐2H‐pyranamines in up to 99 % yield, 99 % ee and more than 95:5 d.r. The catalytic system was also efficient for β‐substituted acyclic enecarbamates, affording more challenging 2,3,4‐trisubstituted 3,4‐dihydro‐2H‐pyranamine with three contiguous stereogenic centers in excellent yields, diastereoselectivities, and enantioselectivities. The reaction could be scaled up to a gram scale with no deterioration of either enantioselectivity or yield. Based on these experiments and on previous reports, a possible transition state was proposed.     

Pd(II)‐Catalyzed Tandem Enantioselective Methylene C(sp3)−H Alkenylation–Aza‐Wacker Cyclization to Access β‐Stereogenic γ‐Lactams

Herein, we describe an unprecedented cascade reaction to β‐stereogenic γ‐lactams involving Pd(II)‐catalyzed enantioselective aliphatic methylene C(sp³)?H alkenylation–aza‐Wacker cyclization through syn‐aminopalladation. Readily available 3,3′‐substituted BINOLs are used as chiral ligands, providing the corresponding γ‐lactams with broad scope and high enantioselectivities (up to 98 % ee).     

Dual Organocatalysis: Asymmetric Allylic–Allylic Alkylation of α,α‐Dicyanoalkenes and Morita–Baylis–Hillman Carbonates

The first highly enantioselective allylic–allylic alkylation of α,α‐dicyanoalkenes and Morita–Baylis–Hillman carbonates by dual catalysis of (DHQD)₂AQN and (S)‐BINOL has been investigated. Excellent stereoselectivities have been achieved for a broad spectrum of substrates (d.r. > 99:1, up to 99 % ee). The multifunctional allylic products could be efficiently converted to a range of complex chiral cyclic frameworks. EWG=electron‐withdrawing group, (DHQD)₂AQN=hydroquinidine (anthraquinone‐1,4‐diyl) diether, (S)‐BINOL =(S)‐(?)‐1,1′‐bi‐2‐naphthol.