Ultrasound effects on the Mn(III) - promoted addition of amidoalkyl radicals to olefins

Amidoalkyl radicals, generated from amides by Mn(OAc)₃ in acetic acid react with phenyl substituted alkenes to generate five-membered lactones or lactams. Ultrasound at ambient temperature significantly accelerates these single electron transfer reactions even when compared with conventional conditions under reflux or simple mechanical stirring. In some cases sonication leads to unusual products.     

Glycosylidene Carbenes. Part 15. Synthesis of disaccharides from allopyranose-derived vicinal 1,2-diols. Evidence for the protonation by a H-bonded hydroxy group in the σ-plane of the intermediate carbene,followed by attack on the oxycarbenium ion in the π-plane

The α-D -allo-diol 9 possesses an intramolecular H-bond (HO? C(3) to O? C(1)) in solution and in the solid state (Fig. 2). In solution, it exists as a mixture of the tautomers 9a and 9b (Fig. 3), which possess a bifurcated H-bond, connecting HO? C(2) with both O? C(1) and O? C(3). In addition, 9a possesses the same intramolecular H-bond as in the solid state, while 9b is characterized by an intramolecular H-bond between HO? C(3) and O? C(4). In solution, the β-D -anomer 12 is also a mixture of tautomers, 12a and presumably a dimer. The H-bonding in 9 and 12 is evidenced by their IR and ¹H-NMR spectra and by a comparison with those of 3–8, 10 , and 11 . The expected regioselectivity of glycosidation of 9 and 12 by the diazirine 1 or the trichloroacetimidate 2 is discussed on the basis of the relative degree of acidity/nucleophilicity of individual OH groups, as governed by H-bonding. Additional factors determining the regioselectivity of glycosidation by 1 are the direction of carbene approach/proton transfer by H-bonded OH groups, and the stereoelectronic control of both the proton transfer to the alkoxy-alkyl carbene (in the σ-plane) and the combination of the thereby formed ions (π-plane of the oxycarbenium ion). Glycosidation of 9 by the diazirine 1 or the trichloroacetimidate 2 proceeded in good yields (75–94%) and with high regioselectivity. Glycosidation of 9 and 12 by 1 or 2 gave mixtures of the disaccharides 14–17 and 18–21 , respectively (Scheme 2). As expected, glycosidation of 12 by 1 or by 2 gave a nearly 1:1 mixture of regioisomers and a slight preference for the β-D -anomers (Table 4). Glycosidation of the α-D -anomer 9 gave mostly the 1,3-linked disaccharides 16 and 17 (α-D β-D ) along with the 1,2-linked disaccharides 14 and 15 (α-D < β-D , 1,2-/1,3-linked glycosides ca. 1:4), except in THF and at low temperature, where the β-D -configurated 1,2-linked disaccharide 15 is predominantly formed. Similarly, glycosidation of 9 with 2 yielded mainly the 1,3-linked disaccharides (1,2-/1,3-linked products ca. 1:3 and α-D /β-D ca. 1:4). Yields and selectivity depend upon the solvent and the temperature. The regioselectivity and the unexpected stereoselectivity of the glycosidation of 9 by 1 evidences the combined effect of the above mentioned factors, which also explain the lack of regio-complementarity in the glycosidation of 9 by 1 and by 2 (Scheme 3). THF solvates the intermediate oxycarbenium ion, as evidenced by the strong influence of this solvent on the regio- and stereoselectivity, particularly at low temperatures, where kinetic control leads to a stereoelectronically preferred axial attack of THF on the oxycarbenium ion.     

Asymmetric Synthesis of α-Aminophosphonic Acids by Cycloaddition of N-Glycosyl-C-dialkoxyphosphonoylnitrones

Addition of dialkyl phosphites to the nitrone 6 , formed in situ from the oxime 5 and formaldehyde gave the hydroxylamines 7 (86%) and 8 (88%), which reacted with p-benzoquinone in the presence of ethylene via the C-dialkoxyphosphonoylnitrones 9 and 10 to yield the cycloaddition products 11 – 14 (80–85%) with a diastereoselectivity of about 50%. The cycloaddition products were transformed into the monoisopropylidene derivatives 15 – 18 and the diacetates 19 – 22 . Comparison of the NMR spectra and the specific rotations of the compounds 19 – 22 with those of the corresponding α-ammo-acid derivatives 23 – 26 of known configuration indicated preferential formation of the L -isomers. The cycloaddition products were transformed in good yield into the L -α-aminophosphonic acids 29 , 30 , 36 , and 39 .     

Kupplungsreaktionen von Diazoniumbetainen mit 1,6-Methano[10]-annulenderivaten und ihre Cyclisierungsreaktionen zu Heterocyclen

Summary Coupling reactions of the diazoniumbetaines2, 4, 6a, 6b, 6c with derivatives of 1,6-methano[10]annulene1a–c and/or -naphthol7 yield the dyes3a–c, 5a, 5c, 8a–c, 9, 11. The syntheses of different triazine derivatives12a–c, 13a–c, 15, 16, and17a, 17c are described.

Herrn Kollegen Gerhard Schwenker mit den besten Wünschen zum 65. Geburtstag gewidmet     

Towards a rigorous treatment of the Jeans-Landau-Teller method for the energy exchanges of harmonic oscillators

For classical Hamiltonian systems containing an harmonic oscillator of high frequency, one has the problem of controlling the energy exchange between the oscillator and the remaining slow degrees of freedom; under very general conditions, such an exchange turns out to be exponentially small with the frequency of the oscillator. In the Jeans-Landau-Teller method, one aims to prove the exponential dependence, and to estimate the coefficient of the exponential, by exploiting the analyticity properties of the solution of the differential equations describing the motion of the system. However, in practice, since the exact solution is not known, such properties are inferred from those of an approximate solution, with no control of the difference; this fact might a priori even invalidate the exponential dependence itself. In the present paper a rigorous treatment is given, for a particular model of interest in the domain of atomic collisions, by keeping control of the difference between the exact and the approximate solution.     

Formation of dinuclear,macrocyclic, and chain structures from HgI(2) and a semirigid benzimidazole-based bridging ligand: an example of ring-opening supramolecular isomerism

The reactions of HgI(2) with the semirigid ditopic ligand 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (bbimms) afforded three new complexes, [Hg(2)(mu-I)(2)I(2)(bbimms)] (1), [Hg(2)I(4)(bbimms)(2)] (2), and catena-poly[HgI(2)(bbimms)] (3). The ligand and all complexes have been structurally characterized by single-crystal X-ray diffraction. 1 is a triply bridged dinuclear complex comprised of two Hg(II) ions, one bridging ligand, two bridging I(-) anions, and two terminal I(-) anions. 2 is a dinuclear metallamacrocycle comprised of two Hg(II) ions, two bridging ligands, and four terminal I(-) anions, while 3 is a helical chain with the repeating unit of HgI(2)(bbimms). 2 and 3 can be classified as supramolecular isomers, and both are related to the triply bridged precursor 1 via the addition of one more ligand in a ring-opening process.     

Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films

Phosphides are interesting candidates for hole transport materials and p-type transparent conducting applications, capable of achieving greater valence band dispersion than their oxide counterparts due to the higher lying energy and increased size of the P 3p orbital. After computational identification of the indirect-gap semiconductor CaCuP as a promising candidate, we now report reactive sputter deposition of phase-pure p-type CaCuP thin films. Their intrinsic hole concentration and hole mobility exceed 1 × 10²⁰ cm⁻³ and 35 cm² V⁻¹ s⁻¹ at room temperature, respectively. Transport calculations indicate potential for even higher mobilities. Copper vacancies are identified as the main source of conductivity, displaying markedly different behaviour compared to typical p-type transparent conductors, leading to improved electronic properties. The optical transparency of CaCuP films is lower than expected from first principles calculations of phonon-mediated indirect transitions. This discrepancy could be partly attributed to crystalline imperfections within the films, increasing the strength of indirect transitions. We determine the transparent conductor figure of merit of CaCuP films as a function of composition, revealing links between stoichiometry, crystalline quality, and opto-electronic properties. These findings provide a promising initial assessment of the viability of CaCuP as a p-type transparent contact.

We synthesize air-stable, p-type CaCuP thin films with high hole concentration and high hole mobility as potential p-type transparent conductors. We study their optoelectronic properties in detail by advanced experimental and computational methods.     

Shear-induced particle segregation in binary mixtures:Verification of a percolation theory

Granular materials composed of different-sized grains may experience undesired segregation.Segrega-tion is detrimental for a lot of industries because it leads ...     

Thiosemicarbazide-Substituted Coumarins as Selective Inhibitors of the Tumor Associated Human Carbonic Anhydrases IX and XII

A novel series of thiosemicarbazide-substituted coumarins was synthesized and the inhibitory effects against four physiologically relevant carbonic anhydrase isoforms I, II, IX and XII showed selective activities on the tumor-associated IX and XII isozymes. Molecular modeling studies on selected compounds 14a and 22a were performed. The binding modes of such compounds were determined assuming their enzymatically active structures (i.e., cinnamic acid) in the thermodynamically favored, and not previously explored, E geometry. Molecular modelling suggests multiple interactions within the enzymatic cavity and may explain the high potency and selectivity reported for the hCAs IX and XII.