Showing papers by "Alexander J. Blake published in 2010"
TL;DR: Overall, gas adsorption measurements on desolvated framework SOF-1a reveal not only high capacity uptakes for C(2)H(1) and CO(2), compared to other crystalline molecular organic solids, but also an adsorptive selectivity in the order C( 2)H (2) > CO(3) > CH(4) > N(2).
Abstract: Reaction of β-amino-β-(pyrid-4-yl)acrylonitrile with the aromatic dicarboxaldehydes 9,10-bis(4-formylphenyl)anthracene and terephthalaldehyde affords the dihydropyridyl products 9,10-bis(4-((3,5-dicyano-2,6-dipyridyl)dihydropyridyl)phenyl)anthracene (L1) and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)benzene (L2), respectively. In the solid state [L1]·2.5DMF·3MeOH (SOF-1) crystallizes in the monoclinic space group P21/c and forms a 3D stable supramolecular organic framework via strong N−H···Npy hydrogen bonds and π−π interactions. The material incorporates pyridyl-decorated channels and shows permanent porosity in the solid state. The pore volumes of the desolvated framework SOF-1a calculated from the N2 isotherm at 125 K and the CO2 isotherm at 195 K are 0.227 and 0.244 cm3 g−1, respectively. The N2 absorption capacity of SOF-1a at 77 K is very low, with an uptake of 0.63 mmol g−1 at 1 bar, although saturation N2 adsorption at 125 K is 6.55 mmol g−1 (or 143 cm3 g−1). At ambient temperature, SOF-...
306 citations
TL;DR: Neutron powder diffraction experiments on D(2)-loaded NOTT-112 reveal that the axial sites of exposed Cu(II) ions in the smallest cuboctahedral cages are the first, strongest binding sites for D( 2) leading to an overall discrimination between the two types of exposure sites at the paddlewheel nodes.
Abstract: Neutron powder diffraction experiments on D2-loaded NOTT-112 reveal that the axial sites of exposed Cu(II) ions in the smallest cuboctahedral cages are the first, strongest binding sites for D2 leading to an overall discrimination between the two types of exposed Cu(II) sites at the paddlewheel nodes. Thus, the Cu(II) centers within the cuboctahedral cage are the first sites of D2 binding with a Cu−D2 distance of 2.23(1) A.
271 citations
TL;DR: Time-resolved infrared measurements showed that the initial excited state formed on ultraviolet irradiation of the rhenium-based metal-organic framework was characteristic of an intra-ligand state, rather than the metal-ligands charge transfer state typically observed in solution, and revealed that the metal -diimine complexes rearranged from the fac- to mer-isomer in the crystalline solid state.
Abstract: Metal−organic frameworks, typically built by bridging metal centres with organic linkers, have recently shown great promise for a wide variety of applications, including gas separation and drug delivery. Here, we have used them as a scaffold to probe the photophysical and photochemical properties of metal−diimine complexes. We have immobilized a M(diimine)(CO)3X moiety (where M is Re or Mn, and X can be Cl or Br) by using it as the linker of a metal−organic framework, with Mn(II) cations acting as nodes. Time-resolved infrared measurements showed that the initial excited state formed on ultraviolet irradiation of the rhenium-based metal−organic framework was characteristic of an intra-ligand state, rather than the metal−ligand charge transfer state typically observed in solution, and revealed that the metal−diimine complexes rearranged from the fac- to mer-isomer in the crystalline solid state. This approach also enabled characterization of the photoactivity of Mn(diimine)(CO)3Br by single-crystal X-ray diffraction.
130 citations
TL;DR: Alpha-diazo-beta-ketosulfones behave similarly and give 5-sulfonyloxazoles upon dirhodium tetrakis(heptafluorobutyramide) catalyzed reaction with carboxamides, which gives the corresponding thiazole-5-carboxylates, -phosphonates, and -sulfones.
Abstract: Dirhodium tetraacetate catalyzed reaction of α-diazo-β-keto-carboxylates and -phosphonates with arenecarboxamides gives 2-aryloxazole-4-carboxylates and 4-phosphonates by carbene N−H insertion and cyclodehydration. In stark contrast, dirhodium tetrakis(heptafluorobutyramide) catalysis results in a dramatic change of regioselectivity to give oxazole-5-carboxylates and 5-phosphonates. α-Diazo-β-ketosulfones behave similarly and give 5-sulfonyloxazoles upon dirhodium tetrakis(heptafluorobutyramide) catalyzed reaction with carboxamides. The analogous reactions of thiocarboxamides give the corresponding thiazole-5-carboxylates, -phosphonates, and -sulfones.
110 citations
TL;DR: It is reported that yttrium carbenes can effect regioselective ortho-C-H activation and sequential C-C and C-O bond formation reactions of aryl ketones to give iso-benzofurans and hydroxymethylbenzophenones.
Abstract: Rare earth carbenes exclusively exhibit Wittig-type reactivity with carbonyl compounds to afford alkenes. Here, we report that yttrium carbenes can effect regioselective ortho-C-H activation and sequential C-C and C-O bond formation reactions of aryl ketones to give iso-benzofurans and hydroxymethylbenzophenones. With MeCOPh, cyclotetramerization occurs giving a substituted cyclohexene. This demonstrates new rare earth carbene reactivity which complements existing Wittig-type reactivity.
101 citations
TL;DR: The synthetic utility of tri-benzyl lanthanide complexes 2-8 and 11 were tested in reactions with the bis-(iminophosphorano)methane H2C(PPh2NSiMe3)2 (H2-BIPM), which afforded [Ln(BIPM)(H-BI PM], which afforded tri-valent [Yb(Bz)3(THF)3] (10) was apparently not formed.
Abstract: Reaction of [Ln(I)3(THF)4] (Ln = Ce, Pr) or [Ln(I)3(THF)3.5] (Ln = Nd, Sm, Gd, Dy, Er) with three equivalents of [KBz] (Bz = CH2C6H5) at 0 °C afforded the corresponding lanthanide tri-benzyl complexes [Ln(Bz)3(THF)3] [Ln = Ce (2), Pr (3), Nd (4), Sm (5), Gd (6), Dy (7), Er (8) La (11)] in 48–75% crystalline yields, with the exception of the redox active samarium complex, which was isolated in poor (20%) yield. Complexes 2–8 were found to adopt distorted octahedral geometries, where the Bz and THF groups are bound in a mutually fac manner in the solid state. Although the series is structurally similar, classification of three structural types can be made on the basis of the lanthanide contraction: (i) complexes which exhibit three η2 Ln⋯Cipso contacts (1–4, 11); (ii) complexes which show one η2 Ln⋯Cipso contact (5); (iii) complexes with no multi-hapto interactions (6–8). For ytterbium, the mixed valence, YbII/YbIII complex [YbII(Bz)(THF)5]+[YbIII(Bz)4(THF)2]− (9) was reproducibly formed at 0 °C and −78 °C as a result of partial (50%) YbIII→ YbII reduction with concomitant formation of half an equivalent of 1,2-diphenylethane by oxidative coupling. Tri-valent [Yb(Bz)3(THF)3] (10) was apparently not formed. The synthetic utility of tri-benzyl lanthanide complexes 2–8 and 11 were tested in reactions with the bis-(iminophosphorano)methane H2C(PPh2NSiMe3)2 (H2-BIPM), which afforded [Ln(BIPM)(H-BIPM)] [Ln = La (12), Ce (13), Pr (14), Nd (15), Sm (16), Gd (17)] and [Ln(BIPM)(Bz)(THF)] [Ln = Dy (18), Er (19)]. Compounds 2–9 and 12–19 have been variously characterised by X-ray crystallography, multi-nuclear NMR spectroscopy, FTIR spectroscopy, room temperature Evans method solution magnetic moments and CHN micro-analyses.
88 citations
TL;DR: Two new three-dimensional Sc(III) metal-organic frameworks show high thermal stability with retention of crystallinity up to 350 °C and enhanced BET surface area and pore volumes calculated from the maximum N(2) adsorption.
Abstract: Two new three-dimensional ScIII metal–organic frameworks {[Sc3O(L1)3(H2O)3]⋅Cl0.5(OH)0.5(DMF)4(H2O)3}∞ (1) (H2L1=1,4-benzene-dicarboxylic acid) and {[Sc3O(L2)2(H2O)3](OH)(H2O)5(DMF)}∞ (2) (H3L2=1,3,5-tris(4-carboxyphenyl)benzene) have been synthesised and characterised. The structures of both 1 and 2 incorporate the trinuclear trigonal planar [Sc3(O)(O2CR)6] building block featuring three ScIII centres joined by a central μ3-O2− donor. Each ScIII centre is further bound by four oxygen donors from four different bridging carboxylate anions, and a molecule of water located trans to the μ3-O2− donor completes the six coordination at the metal centre. Frameworks 1 and 2 show high thermal stability with retention of crystallinity up to 350 °C. The desolvated materials 1 a and 2 a, in which the solvent has been removed from the pores but with water or hydroxide remaining coordinated to ScIII, show BET surface areas based upon N2 uptake of 634 and 1233 m2 g−1, respectively, and pore volumes calculated from the maximum N2 adsorption of 0.25 cm3 g−1 and 0.62 cm3 g−1, respectively. At 20 bar and 78 K, the H2 isotherms for desolvated 1 a and 2 a confirm 2.48 and 1.99 wt % total H2 uptake, respectively. The isosteric heats of adsorption were estimated to be 5.25 and 2.59 kJ mol−1 at zero surface coverage for 1 a and 2 a, respectively. Treatment of 2 with acetone followed by thermal desolvation in vacuo generated free metal coordination sites in a new material 2 b. Framework 2 b shows an enhanced BET surface area of 1511 m2 g−1 and a pore volume of 0.76 cm3 g−1, with improved H2 uptake capacity and a higher heat of H2 adsorption. At 20 bar, H2 capacity increases from 1.99 wt % in 2 a to 2.64 wt % for 2 b, and the H2 adsorption enthalpy rises markedly from 2.59 to 6.90 kJ mol−1.
74 citations
TL;DR: U{C(PPh2NMes)2}2] is the first homoleptic uranium bis(carbene) complex with two formal U=C double bonds.
Abstract: Treatment of H2C(PPh2NMes)2 (1, Mes = 2,4,6-Me3C6H2) with two equivalents of ButLi afforded the methandiide complex [Li2{C(PPh2NMes)2}2]2 (2); reaction of 2 with [UI3(THF)4] gave [U{C(PPh2NMes)2}2] (3), which is the first homoleptic uranium bis(carbene) complex with two formal UC double bonds.
72 citations
TL;DR: A newly developed microfabricated polydimethylsiloxane (PDMS) device is presented that can be utilized for experiments implementing the Boyden chamber for in vitro hypoxic studies, allowing experiments to be conducted faster and with more precision than currently possible.
Abstract: Cell migration is a hallmark of cancer cell metastasis and is highly correlated with hypoxia in tumors. The Boyden chamber is a porous membrane-based migration platform that has seen a great deal of use for both in vitro migration and invasion assays due to its adaptability to common culture vessels and relative ease of use. The hypoxic chamber is a current tool that can be implemented to investigate the cellular response to oxygen paradigms. Unfortunately, this method lacks the spatial and temporal precision to accurately model a number of physiological phenomena. In this article, we present a newly developed microfabricated polydimethylsiloxane (PDMS) device that easily adapts to the Boyden chamber, and provides more control over the oxygenation conditions exposed to cells. The device equilibrates to 1% oxygen in about 20 min, thus demonstrating the capabilities of a system for researchers to establish both short-term continuous and intermittent hypoxia regimes. A Parylene-C thin-film coating was used to prevent ambient air penetration through the bulk PDMS and was found to yield improved equilibration times and end-point concentrations. MDA-MD-231 cells, an invasive breast cancer line, were used as a model cell type to demonstrate the effect of oxygen concentration on cell migration through the Boyden chamber porous membrane. Continuous hypoxia downregulated migration of cells relative to the normoxic control, as did an intermittent hypoxia regime (IH) cycling between 0% and 21% oxygen (0–21% IH). However, cells exposed to 5–21% IH exhibited increased migration compared to the other conditions, as well as relative to the normoxic control. The results presented here show the device can be utilized for experiments implementing the Boyden chamber for in vitro hypoxic studies, allowing experiments to be conducted faster and with more precision than currently possible.
59 citations
57 citations
TL;DR: In this paper, attempts to prepare [Dy{C(PPh2NSiMe3)2}(I)(THF)2] (1) from in situ prepared "[Dy(Bn)2(I(THF)" (2) = C6H5CH2).
TL;DR: A novel brain slice recording chamber design that provides a stable microfluidic perfusion environment in which tissue health is optimized by superfusing both surfaces of the slice and measuring current sources and sinks during theta burst stimuli that lead to the induction of long-term potentiation in hippocampal slices is presented.
TL;DR: In this paper, the binding and extraction of Ag(I) by tripodal Schiff-base ligands incorporating different aromatic podand arms are reported, and the structures of 1 and of four AgI complexes are determined by single crystal X-ray diffraction.
Abstract: The binding and extraction of Ag(I) by tripodal Schiff-base ligands incorporating different aromatic podand arms are reported. These ligands have been synthesized by condensation of tris(2-aminoethyl)amine with benzaldehyde (1), 4-phenylbenzaldehyde (2), 2- (3) and 4-pyridinecarbaldehyde (4). The structures of 1 and of four Ag(I) complexes [Ag(1)]ClO4, [Ag(2)]ClO4, [Ag3(3)2](ClO4)3 and {[Ag3(4)2](ClO4)3}n have been determined by single crystal X-ray diffraction. The structure of 1 shows intramolecular C–H⋯π (aromatic) interactions between phenyl rings, while bonding of Ag(I) via Ag–N interactions within the ionophore pocket is confirmed. In [Ag(1)]ClO4, and [Ag(2)]ClO4 additional long-range Ag–H interactions are observed, while π–π stacking occurs in the polynuclear species [Ag3(3)2](ClO4)3 and {[Ag3(4)2](ClO4)3}n. Potentiometric titration, liquid–liquid extraction and 1H NMR spectroscopic studies were performed to probe the nature of the silver complexes in solution. Potentiometric studies confirm increasing complex stability with Ag(I) in the order 2 < 4 < 1 < 3, and enhanced Ag(I) extraction efficiency was observed with both increasing lipophilicity of the ionophore and the presence of additional donor groups. 1H NMR spectroscopic studies were employed to probe the solution complexation behaviour of 1–4 towards Ag(I) and these confirm the formation of primarily 1 : 1 Ag : L complexes in solution.
TL;DR: It is clear that bond rearrangements from imine-pyrrole to amine-azafulvene tautomers occur on metal co-ordination, both in the solid state and in solution.
Abstract: The synthesis and structures of Fe, Co, and Zn halide complexes [MX2(H2L)] (M = Fe, X = Br; M = Co, Zn, X = Cl) of the N-donor extended dipyrromethane ligand H2L are described, from which it is clear that bond rearrangements from imine-pyrrole to amine-azafulvene tautomers occur on metal co-ordination, both in the solid state and in solution. In the structure of [FeBr2(H2L)], this H-migration results in a pendant amine that is involved in both inter- and intramolecular hydrogen bonds to the bromide ligands, so forming a dimer. As the tautomerisation renders the N–H protons less acidic, metal-based ligand substitution reactions can occur in favour of deprotonation. As such, the reaction between [MCl2(H2L)] (M = Co, Zn) and NaN3 results in the formation of the bis(azide) complexes [M(N3)2(H2L)] which for Co displays both inter- and intramolecular N–H⋯N3–Co hydrogen bonds in the solid state. In contrast, reactions of the dihalides with the lithium bases LiNMe2 or LiMe (M = Fe), or reduction reactions with C8K (M = Fe, Co) result in the formation of the known dinuclear helicates [M2(L)2].
TL;DR: Three-fold deprotonation of 1 with n-butyllithium afforded the corresponding tri-lithium tris(N-arylamido-dimethylsilyl)methane etherate [HC{SiMe(2)N(Li)Ar}(3)(OEt(2))] (2) in 92% yield.
Abstract: Reaction of three equivalents of ArNH(2) (Ar = 3,5-Me(2)C(6)H(3)) with HC(SiMe(2)Br)(3) in the presence of the auxiliary base NEt(3) afforded the tripodal tris(N-arylamine-dimethylsilyl)methane HC{SiMe(2)N(H)Ar}(3) (1) in 83% yield. Three-fold deprotonation of 1 with n-butyllithium afforded the corresponding tri-lithium tris(N-arylamido-dimethylsilyl)methane etherate [HC{SiMe(2)N(Li)Ar}(3)(OEt(2))] (2) in 92% yield. Salt elimination reactions between 2 or the known complex [HC{SiMe(2)N(Li)Ar'}(3)(OEt(2))(2)] (3) (Ar' = 4-MeC(6)H(4)) with one equivalent of uranium(IV) tetrachloride afforded the corresponding tris(N-arylamido-dimethylsilyl)methane uranium(IV) chloride complexes as monomeric [U(Cl){HC(SiMe(2)NAr)(3)}(THF)] (4) and dinuclear [{HC(SiMe(2)NAr')(3)}U(Cl)(mu-Cl)U(THF)(2){(Ar'NSiMe(2))(3)CH}] (5) species in 70 and 90% crystalline yields, respectively. Treatment of 4 and 5 with one equivalent of trimethylsilyl iodide resulted in halide exchange and formation of [U(I){HC(SiMe(2)NAr)(3)}(THF)(2)] (6) and [U(I){HC(SiMe(2)NAr')(3)}(THF)] (7) in 85 and 90% yields, respectively. The heteroleptic amide [U(NCy(2)){HC(SiMe(2)NAr)(3)}(THF)] (8) was prepared from the reaction between 4 and one equivalent of lithium dicyclohexylamide and was isolated in 78% yield. Analogous attempts to prepare [U(NCy(2)){HC(SiMe(2)NAr')(3)}(THF)] (9) from 5 consistently resulted in intractable mixtures of products. Complexes 1-8 have been characterised by X-ray crystallography, NMR spectroscopy, FTIR spectroscopy, room temperature Evans method solution magnetic moments, and CHN micro-analyses.
TL;DR: In this article, the synthesis of co-ordination polymers derived from T-shaped transition metal dipicolinate fragments [M(dipic)] (M = Co, Ni; dipic2− = dipic, pyridine-2,6-dicarboxylate) has been investigated.
Abstract: The synthesis of co-ordination polymers derived from T-shaped transition metal dipicolinate fragments [M(dipic)] (M = Co, Ni; dipic2− = dipicolinate, pyridine-2,6-dicarboxylate) has been investigated. The use of mononuclear precursors such as [Co(dipic)(OH2)(OSMe2)2] 1 for the synthesis of 4,4′-bipyridine-bridged complexes showed limited success, direct reaction of individual components being found to be more effective. Thus, reaction of transition metal(II) cations with the dipicolinate anion in the presence of 4,4′-bipyridine (4,4′-bipy) under a variety of reaction conditions affords co-ordination complexes with [M(dipic)]:4,4′-bipy molar ratios of 1 : 1, 2 : 1 and 2 : 3. In the 2 : 1 complexes, {[{Co(dipic)(OH2)2}2{μ-4,4′-bipy}]·nH2O}∞3 (n = 4), 4 (n = 3) the co-ordination geometry at the metal centre is completed by one N-donor bridge and two water molecules. The resulting binuclear building blocks are assembled into 3D matrices by complex hydrogen-bonding networks. In the 1 : 1 polymers, {[{Co(μ-dipic)}(μ-4,4′-bipy)]·n(solvent)}∞ [n(solvent) = 3H2O 5, H2O·MeOH 2, or 2H2O·0.5Me2SO 6] the metal centre co-ordination geometry is completed by two N-donor bridges and an oxygen atom of a bridging dipicolinate anion. The extended structure thus comprises a series of [Co(dipic)]∞ chains bridged by 4,4′-bipyridine molecules to give a 2D structure with (4,4) topology. Π–π stacking interactions between dipicolinate anions of adjacent [Co(dipic)]∞ chains lead to 3D networks with spacious channels occupied by diverse solvent molecules. Replacement of 4,4′-bipyridine by the longer bridge, trans-4,4′-azobis(pyridine) (azpy) in {[{Ni(μ-dipic)}(μ-azpy)]·H2O·azpy}∞8 provides sufficient space in the channels for the inclusion of a non-co-ordinated azpy molecule at the expense of solvent molecules. In the 2 : 3 polymer, {[Ni(dipic)(μ-4,4′-bipy)1.5]·H2O·Me2SO}∞7, the metal centre co-ordination geometry is completed by three N-donor bridges thus generating the classical T-shaped connecting unit, which leads to a 2D structure of (6,3) topology. Π–π stacking interactions analogous to those found in the 1 : 1 complexes result in a distortion of the classical brickwall architecture, each brick adopting a bow-tie-like topology.
TL;DR: A total synthesis of (+)-cymbodiacetal has been completed from (R)-(+)-limonene oxide using a hetero-Diels-Alder cycloaddition as a key step, and the two diastereomeric spirochroman products are isolable, stable products.
Abstract: A total synthesis of (+)-cymbodiacetal (1) has been completed from (R)-(+)-limonene oxide using a hetero-Diels−Alder cycloaddition as a key step. The key Diels−Alder cycloaddition proceeds with end...
TL;DR: In this paper, a reaction of 2-(2',6'-diethylphenylazo)-4-methylphenol (L 2 ) with [Ir(PPh 3 ) 3 Cl] afforded two organoiridium complexes 3 and 4 via C-H bond activation of an ethyl group in the arylazo fragment of the L 2 ligand.
TL;DR: In this paper, it was shown that bis(bromodimethylsilyl)methane (BrSiMe2)2CH2 (1) with two equivalents of 2,6-diisopropylphenol (Ar′OH) in the presence of the auxiliary base NEt3 enables the bis(aryloxysilyl),methanes (BnSiMethane)2 CH2 (2) as a colourless oil following work-up.
TL;DR: The sterically demanding pyridines 2,6-Ar2C6H3N [Ar = 2,4-6-Me3C 6H2] were prepared by a palladium catalysed Kumada C-C coupling reaction in high yield as mentioned in this paper.
TL;DR: The data presented confirms that Fe(3+) binds tightly to the unstable penta-axial conformation of myo-inositol phosphates possessing the 1,2,3-trisphosphate motif.
Abstract: myo-Inositol phosphates possessing the 1,2,3-trisphosphate motif share the remarkable ability to completely inhibit iron-catalysed hydroxyl radical formation. The simplest derivative, myo-inositol 1,2,3-trisphosphate [Ins(1,2,3)P3], has been proposed as an intracellular iron chelator involved in iron transport. The binding conformation of Ins(1,2,3)P3 is considered to be important to complex Fe3+ in a ‘safe’ manner. Here, a pyrene-based fluorescent probe, 4,6-bispyrenoyl-myo-inositol 1,2,3,5-tetrakisphosphate [4,6-bispyrenoyl Ins(1,2,3,5)P4], has been synthesised and used to monitor the conformation of the 1,2,3-trisphosphate motif using excimer fluorescence emission. Ring-flip of the cyclohexane chair to the penta-axial conformation occurs upon association with Fe3+, evident from excimer fluorescence induced by π–π stacking of the pyrene reporter groups, accompanied by excimer formation by excitation at 351 nm. This effect is unique amongst biologically relevant metal cations, except for Ca2+ cations exceeding a 1:1 molar ratio. In addition, the thermodynamic constants for the interaction of the fluorescent probe with Fe3+ have been determined. The complexes formed between Fe3+ and 4,6-bispyrenoyl Ins(1,2,3,5)P4 display similar stability to those formed with Ins(1,2,3)P3, indicating that the fluorescent probe acts as a good model for the 1,2,3-trisphosphate motif. This is further supported by the antioxidant properties of 4,6-bispyrenoyl Ins(1,2,3,5)P4, which closely resemble those obtained for Ins(1,2,3)P3. The data presented confirms that Fe3+ binds tightly to the unstable penta-axial conformation of myo-inositol phosphates possessing the 1,2,3-trisphosphate motif.
TL;DR: In this paper, the reaction of cuprates derived from R3MgBr/CuI/LiBr with R1C CCH(O2CR2)2 to allenyl esters was investigated.
TL;DR: The presence of an additional Na...H-C agostic interaction potentially contributes to the distortion around the bridging oxide group.
Abstract: The solid-state structure of the title compound, [Na(2)Mn(2)(C(32)H(56)N(2)OSi(2))(2)O(2)] or [1,8-C(10)H(6)(NSi(i)Pr(3))(2)Mn(mu(3)-O)Na(THF)](2), which lies across a crystallographic twofold axis, exhibits a central [Mn(2)O(2)Na(2)](4+) core, with two oxide groups, each triply bridging between the two Mn(III) ions and an Na(+) ion. Additional coordination is provided to each Mn(III) centre by a 1,8-C(10)H(6)(NSi(i)Pr(3))(2) [1,8-bis(triisopropylsilylamido)naphthalene] ligand and to the Na(+) centres by a tetrahydrofuran molecule. The presence of an additional Na...H-C agostic interaction potentially contributes to the distortion around the bridging oxide group.
TL;DR: H 9 PSi 3 cristallise dans P2 1 /c avec a=6,0631, b=12,731, c=9,6784 A, β=92,872°, Z=4, T=100 K; affinement jusqu'a R=0,0287 as discussed by the authors.
Abstract: H 9 PSi 3 cristallise dans P2 1 /c avec a=6,0631, b=12,731, c=9,6784 A, β=92,872°, Z=4, T=100 K; affinement jusqu'a R=0,0287. Les molecules individuelles possedent une symetrie C 3v non cristallographique. Elles sont liees par des liaisons intermoleculaires P...Si et forment des structures en feuilles striees, avec des angles P-Si...P proches de 180° et une coordination de [3+2] autour du phosphore
TL;DR: A formal synthesis of (+)-lactacystin from hydroxymethylglutamic acid (HMG), with an alkylidene carbene insertion reaction being used to construct the key nitrogen-bearing quaternary centre has been completed as mentioned in this paper.
Abstract: A formal synthesis of (+)-lactacystin from hydroxymethylglutamic acid (HMG), with an alkylidene carbene insertion reaction being used to construct the key nitrogen-bearing quaternary centre has been completed. Our route intercepts that of Shibasaki at an advanced pyrrolidinone intermediate, from which the synthesis can be completed following Donohoe's route.
TL;DR: In contrast, dirhodium tetrakis(heptafluorobutyramide) catalysis results in a dramatic change of regioselectivity to give oxazole-5-carboxylates and 5-phosphonates as mentioned in this paper.
Abstract: Dirhodium tetraacetate catalyzed reaction of α-diazo-β-keto-carboxylates and -phosphonates with arenecarboxamides gives 2-aryloxazole-4-carboxylates and 4-phosphonates by carbene N−H insertion and cyclodehydration. In stark contrast, dirhodium tetrakis(heptafluorobutyramide) catalysis results in a dramatic change of regioselectivity to give oxazole-5-carboxylates and 5-phosphonates. α-Diazo-β-ketosulfones behave similarly and give 5-sulfonyloxazoles upon dirhodium tetrakis(heptafluorobutyramide) catalyzed reaction with carboxamides. The analogous reactions of thiocarboxamides give the corresponding thiazole-5-carboxylates, -phosphonates, and -sulfones.
TL;DR: A base labile urethane (Bnpeoc) group derived from 2,2-bis(4′-nitrophenyl)ethan-1-ol has been developed as an amine protecting group as discussed by the authors.
Abstract: A base labile urethane (Bnpeoc) group derived from 2,2-bis(4′-nitrophenyl)ethan-1-ol has been developed as an amine protecting group. This protecting group may be cleaved using the reagents DBN, DBU, DBU/HOAc and piperidine. The preparations of Nα-Bnpeoc amino acids and applications to peptide/glycopeptide synthesis are described.
TL;DR: In this article, the alkylation of N-methylisoindoline-borane complex, using nBuLi in THF is diastereoselective, the substitution occurring predominantly syn to the borane group.
Abstract: The alkylation of N-methylisoindoline–borane complex, using nBuLi in THF is diastereoselective, the substitution occurring predominantly syn to the borane group. Use of the sBuLi–sparteine reagent mixture in Et2O changes the diastereoselectivity observed and enables the reaction to be conducted enantioselectively, giving the chiral isoindoline–borane complexes in up to 89% ee. The relative and absolute configurations of the chiral products were established by X-ray structure determinations and NMR studies. The new asymmetric process is shown to be an enantioselective deprotonation reaction, and the intermediate organolithium is shown to be epimerisable.