Synthèses de produits organofluorés VI Solvolyse de chlorofluorocyclopropanes

Fluoro-organic Syntheses VI: The Solvolysis of Chlorofluoro-cyclopropanes 2-Fluoro-allylic carbocations, generated from 1-chloro-1-fluoro-cyclopropanes or 2-fluoro-allyl p-toluene-sulfonates in water or acetic acid, undergo either proton loss or addition of hydroxyl or acetoxyl. In the latter case, an alkyl-substituted 2-fluoro-allyl ion leads predominantly to the more branched product (e.g. 3-fluoro-2-methyl-3-buten-2-ol) which may be converted into the less branched one (e.g. 2-fluoro-3-methyl-2-buten-2-ol) through reversible reactions.     

Mössbauer study of the three-coordinate planar Fe(II) thiolate complex [Fe(SR)(3)](-) (R = C(6)H(2)-2,4,6-tBu(3)): model for the trigonal iron sites of the MoFe(7)S(9):homocitrate cofactor of nitrogenase

The cofactor (M-center) of the MoFe protein of nitrogenase, a MoFe(7)S(9):homocitrate cluster, contains six Fe sites with a (distorted) trigonal sulfido coordination. These sites exhibit unusually small quadrupole splittings, Delta E(Q) approximately 0.7 mm/s, and isomer shifts, delta approximately 0.41 mm/s. M?ssbauer and ENDOR studies have provided the magnetic hyperfine tensors of all iron sites in the S = 3/2 state M(N). To assess the intrinsic zero-field splittings and hyperfine parameters of the cofactor sites, we have studied with M?ssbauer spectroscopy two salts of the three-coordinated Fe(II) thiolate complex [Fe(SR)(3)](-) (R = C(6)H(2)-2,4,6-tBu(3)). One of the salts, [Ph(4)P][Fe(SR)(3)] x 2MeCN x C(7)H(8), 1, has a planar geometry with idealized C(3h) symmetry. This S = 2 complex has an axial zero-field splitting with D = +10.2 cm(-1). The magnetic hyperfine tensor components A(x) = A(y) = -7.5 MHz and A(z) = -29.5 MHz reflect an orbital ground state with d(z(2)) symmetry. A(iso) = (A(x) +A(y) +A(z))/3 = -14.9 MHz, which includes the contact interaction (kappa P = -21.9 MHz) and an orbital contribution (+7 MHz), which is substantially smaller than A(iso) approximately -22 MHz of the tetrahedral Fe(II)(S-R)(4) sites of both rubredoxin and [PPh(4)](2)[Fe(II)(SPh)(4)]. The largest component of the electric field gradient (EFG) tensor is negative, as expected for a d(z(2)) orbital. However, Delta E(Q) = -0.83 mm/s, which is smaller than expected for a high-spin ferrous site. This reduction can be attributed to a ligand contribution, which in planar complexes provides a large positive EFG component perpendicular to the ligand plane. The isomer shift of 1, delta = 0.56 mm/s, approaches the delta-values reported for the six trigonal cofactor sites. The parameters of 1 and their importance for the cofactor cluster of nitrogenase are discussed.     

Prescriptions and Ingredients for Controlled CC Bond Formation with Organometallic Reagents. New synthetic methods (5)

Merits and drawbacks of known carbon-carbon linking procedures are outlined. Two novel methods are discussed in some detail: the copper-catalyzed alkylation of Grignard reagents and reactions with allylpotassium compounds. Both methods provide a very efficient access to saturated, unsaturated, as well as functionally substituted hydrocarbons and moreover permit an astonishing degree of regio- and stereoselective control of olefin synthesis.     

Silacyclohexadienylanionen bis- und tris-trimethylsilyl)-silacyclohexadiene

1,1-Dialkyl(1,1-diaryl)-4-R-1-silacyclohexadienyl anions (1) are available by ether cleavage of the corresponding, 1,1-dialkyl(1,1-diaryl)-4-methoxy-4-R-1-silacyclohexa-2,5-dienes (4), or by deprotonation of the 1,1-dialkyl(1,1-diaryl)-4-R-1-silacyclohexa-2,4-dienes (3) - which are available from 4 - with n-BuLi or LDA resp.The anions 1 are regioselectively silylated by trimethylchlorosilane to give the 6-trimethylsilyl-1-silacyclohexa-2,4-dienes (7,8), their alkylation or acylation occurs exclusively in 4-position to 16 or 17 resp.Deprotonation of 7, 8 with n-BuLi gives the 2-trimethylsilyl-1-silacyclohexadienyl (9), with trimethylchlorosilane they react regioselectively to give the 2,6-bis(trimethylsilyl)-1-silacyclohexa-2,4-dienes (10, 11), with alkyl halides and ketones the anion 9 reacts only in the 4-position.The 1-silacyclohexa-2,5-dienes 22, 25, 28 substituted at the silicon atom by functional groups (O-i-Prop) or by hydrogen can be transformed into 2,6-bis(trimethylsilyl)-1-silacyclohexa-2,4-dienes 24, 27, 33 resp., if LDA is used as base.The easily formed 4-R-2,6-bis(trimethylsilyl)-1-silacyclohexa-2,4-dienyl anions (by deprotonation of 10, 11, 24, 27, 33 with LDA) react with trimethylchlorosilane regioselectively to give the 4-R-2,4,6-tris(trimethylsilyl)-1-silacyclohexa-2,5-dienes 37. Accessing 37 succeeds very simply by manifold-silylation of the 1-sila-2,4-cyclohexadienes 38 with excess trimethylchlorosilane in the presence of 3 mol LDA.Owing to trimethylsilyl substitution in the 2,6-position of the 1-silacyclohexa-2,4-dienes, the ring-silicon atom is strongly sterically shielded, therefore reactions of functional groups at the silicon atom are restricted.     

Chelatbildung mit N-unsubstituierten 1.2-Diiminliganden

Fe^II, Co^III, Ni^II, Pd^II, and Rh^III chelates with the N-unsubstituted 1-2-diimine ligands benzildiimine and 9.10-phenanthrenequinonediimine have been prepared. The compounds are characterised chemically, spectroscopically (uv, vis, ir) and polarographically. The results indicate remarkable π-back bonding in the chelates. The unusual magnetic moments of the Fe^II, Co^III and Rh^III chelates are caused by temperature-independent paramagnetism. Fe^II, Co^III, Ni^II and Cu^II chelates of the partially deprotonated phenanthrenequinone diimine are obtained.     

Proteome Analysis of Aflibercept Intervention in Experimental Central Retinal Vein Occlusion

Aflibercept is a frequently used inhibitor of vascular endothelial growth factor (VEGF) in the treatment of macular edema following central retinal vein occlusion (CRVO). Retinal proteome changes following aflibercept intervention in CRVO remain largely unstudied. Studying proteomic changes of aflibercept intervention may generate a better understanding of mechanisms of action and uncover aspects related to the safety profile. In 10 Danish Landrace pigs, CRVO was induced in both eyes with an argon laser. Right eyes were treated with intravitreal aflibercept while left control eyes received isotonic saline water. Retinal samples were collected 15 days after induced CRVO. Proteomic analysis by tandem mass tag-based mass spectrometry identified a total of 21 proteins that were changed in content following aflibercept intervention. In retinas treated with aflibercept, high levels of aflibercept components were reached, including the VEGF receptor-1 and VEGF receptor-2 domains. Fold changes in the additional proteins ranged between 0.70 and 1.19. Aflibercept intervention resulted in a downregulation of pigment epithelium-derived factor (PEDF) (fold change = 0.84) and endoplasmin (fold change = 0.91). The changes were slight and could thereby not be confirmed with less precise immunohistochemistry and Western blotting. Our data suggest that aflibercept had a narrow mechanism of action in the CRVO model. This may be an important observation in cases when macular edema secondary to CRVO is resistant to aflibercept intervention.     

Investigation of the NMR enhancement factor in CuMn spin glasses

The NMR enhancement factor of a frozenCuMn spin glass has been measured at a temperatureT?T _g /5. The measurements were performed as function of static magnetic fields of different directions. A two component model of a spin glass has been outlined. One component being a “system of single spins” and the other one being a “subsystem of clusters”. Both components were attributed to different kinds of interaction being RKKY and dipole interaction respectively. The effective anisotropy field of the single spin system consists of two unidirectional contributionsH _a ^s andH _a ^c , which have been measured for different conditions. A second anisotropy fieldH _d binds the cluster system to the system of single spins. All anisotropy fields depend on the annealing temperature of the alloys.     

A nonterminating 8φ7 summation for the root system Cr

Using multiple q-integrals and a determinant evaluation, we establish a nonterminating ₈φ₇ summation for the root system C_r. We also give some important specializations explicitly.     

«3-Fluorisopren» (2-Fluor-3-methyl-1,3-butadien) und einige heterosubstituierte Abkömmlinge

‘3-Fluoroisoprene’ (2-Fluoro-3-methyl-1,3-butadiene) and Some Hetero-substituted Derivatives Thereof The readily accessible 1-chloro-1-fluoro-2-iodomethyl-2-methylcyclopropane undergoes zinc-promoted ring-cleavage yielding 2-fluoro-3-methyl-1, 3-butadiene (‘3-fluoroisoprene’) in almost quantitative yield. Alternatively the iodine atom may be replaced by electron-attracting groups such as cyano, benzenesulfonyl or triphenylphosphonio. Ring-opening of the resulting derivatives can then be brought about by various bases and leads to substituted fluorodienes. - The chemical reactivity of ‘3-fluoroisoprene’ has been studied in some detail. For example, it was found to add bromine at temperatures below 0° under kinetic control and to afford mainly the 1,4-adduct having the (Z)-configuration besides smaller quantities of the 1,2- and 3,4-adduct. At room temperature this mixture slowly undergoes a transformation yielding, as the sole products, both stereoisomeric 1, 4-adducts in a 1:1 ratio.