bluuebunny/crossref_metadata_2025_split huggingface dataset:
ʟ(-)Sorbose als Inhibitor der intestinalen Vitamin B12-Resorption
Authors: Heinrich H. C. , Skibbe R. , Staak M. 
Published: March 2015

1. 10 g ʟ (-) Sorbose hemmen bei etwa einem Drittel der daraufhin mit Hilfe des Radio-B12-Urincxkretions-Testes untersuchten Menschen mit normaler Vitamin B12-Resorption die intestinale Resorption einer physiologischen Radio-Vitamin B12-Testdosis von 0,5 μg beträchtlich, während bei den verbleibenden zwei Dritteln entweder keine Beeinflussung der Vitamin B12-Resorption oder aber ein zwischen 20 und 50% liegender Anstieg der Radio-B12-Harnexkretion beobachtet wurde. Eine weitere Heraufsetzung der Sorbosedosis (bis auf 50 g) ist dann fast stets von einer Hemmung der Vitamin B12-Resorption begleitet.
2. Heterologer Intrinsic Factor ist zumindestens teilweise in der Lage, den Inhibitoreffekt der Sorbose auf die intestinale Vitamin B12-Resorption beim Menschen zu kompensieren.
3. Bei Patienten mit gestörter Vitamin B12-Resorption (perniciöse Anämie bzw. einheimische Sprue) hatten ʟ (-) Sorbose und ᴅ (-) Sorbit in Mengen von 0,1 - 1 g bzw. 10 g eine zwar sehr geringe aber dennoch deutlich fördernde Wirkung auf die Radio-B12-Resorption, die jedoch im Vergleich mit dem wesentlich stärkeren Effekt von 12 mg Intrinsic Factor-Konzentrat unbedeutend und für eine praktische Perniciosa-Therapie uninteressant ist.
4. Auch bei normalen Schweinen und Meerschweinchen wird die intestinale Resorption physiologischer Radio-B12-Testdosen von 0,5 μg bzw. 30 ng durch 20 g bzw. 100 mg ʟ (-) Sorbose stark gehemmt, wie mit dem Faeces- und Urinexkretions-Test bzw. mit dem Leberinkorporations-Test durchgeführte Untersuchungen ergaben.
5. Der mögliche Wirkungsmechanismus des Sorbose-Hemmeffektes auf die intestinale Vitamin B12-Resorption beim Menschen, Schwein und Meerschweinchen wird auf Grund der schon unter in vitro-Bedingungen papierchromatographisch nachgewiesenen Bildung eines Sorbose-Vitamin B12- bzw. Sorbit-Vitamin B12-Komplexes diskutiert.
Über die Wirkung von Dunkelheit auf den Proteingehalt kernhaltiger und kernloser Zellteile von Acetabularia mediterranea
Authors: Werz Günther 
Published: March 2015

In darkened nucleate and enucleate cell parts of the uninuclear marine green alga Acetabularia mediterranea the protein content decreases. This holds for the total protein as well as for chloroplast protein. It seems, that also a decrease of cytoplasmic protein occurs, but that it is masked by protein released from the chlloroplast fraction.
No difference could be found between the decrease of the protein in nucleate and enucleate cell parts. Beside the total protein decrease a transport of stalk protein into the rhizoids occurs in the nucleate parts.
The results are compared with those found at starving nucleate and enucleate halves of Amoeba.
Ultrazentrifugen-Untersuchungen zum Sedimentations-Verhalten isolierter γ-Globuline Gesunder und Krebskranker
Authors: Wetter O. , Hertenstein Ch. , Jahnke K. , Merten R. 
Published: March 2015

1. Ultracentrifugal studies on six γ-globulin preparations isolated with DEAE-cellulose from single and pooled sera taken from normal individuals and cancer patients showed significant differences between the two groups. Whereas the slopes of the concentration regression lines in the normal group were about 0.9, they were about 0.6 in the cancer group with the exception of one case. The s20· 1013 values in the two groups are similar when extrapolated to infinite dilution (intrinsic sedimentation coefficient). The results can be interpreted by the presence of a γ-globulin in the cancer group which differs from the γ-globulins of sound individuals in its sedimentation behaviour.
2. The mean value of the intrinsic sedimentation coefficient of γ-globulin fractionated exclusively by DEAE chromatography corresponds to the value which is found for electrophoretically isolated γ-globulin.
Solution Structures of Pyrophthalones, I Structure and Conformation of 1,3-Indandionato-2(2-pyridinium)-betaïn — a 1H/13C NMR Approach
Authors: Haupt Erhard T. K. , Dieck Heindirk tom , Bontchev Panayot R. 
Published: March 2015

Abstract
The complete analysis of the 1H/13 C NMR spectra of α-Pyrophthalone and related compounds demonstrates that the earlier static planar description of the molecules is invalid for polar sol-vents, and here the stability of any intramolecular hydrogen bond is small.
Konkurrierende Koordination von Kronenethern, Perchloratanionen und Lösungsmittelmolekülen am Co(II)-Ion — Eine Leitfähigkeits-und NMR-Studie in Nitromethan / Competitive Coordination of Crown Ethers, Perchlorate Anions and Solvent Molecules at Co(II)-Ions — A Conductivity and NMR Study on Nitromethane
Authors: Dickert Franz L. , Vonend Michael W. 
Published: March 2015

Abstract
The 1:1 complexes between Co(II) and the crown ethers dibenzo[24]crown-8, dibenzo[18]-crown-6 and [18]crown-6 show a molar conductivity in nitromethane which indicates coordination of even perchlorate anions. The substitution of this anion by solvent molecules can be monitored by conductometric titrations. This procedure reveals that dibenzo[24]crown-8 and [18]crown-6 is a potent five dentate ligand whereas dibenzo[18]crown-6 strongly coordinates only via three donor atoms. The mixed complexes with crown ether and methanol show strong outer-sphere associa-tion with the Perchlorate anions, which can be confirmed by investigations with [15]crown-5 complexes.
Ru2(CO)6(ButNS) − Ein tert-Butylschwefelimid-Komplex mit Ru2NS-Tetrahedrangerüst / Ru2(CO)6(BUtNS) - A tert-Butyl Sulfur Imide Complex Containing a Ru2NS Tetrahedrane Skeleton
Authors: Herberhold Max , Bühlmeyer Wolfgang , Gieren Alfred , Hübner Thomas , Wu J. 
Published: March 2015

Abstract
Fragmentation of bis(rm-butyl) sulfur diimide, S(NBut)2 (1a), in the presence of Ru3(CO)12 leads to a yellow tetrahedrane-type complex Ru2(CO)6(ButNS) (3a) containing tert-butyl sulfur imide as a six-electron ligand. According to the X-ray structure determination the N−S bond (1.716 Å) is arranged perpendicular to the Ru−Ru axis (2.661 Å).
A Study on the Mannich Reaction with 1-Phenylamino-3-indenone
Authors: Hammouda M. , Hamama W. S. , Afsah E. M. 
Published: March 2015

Abstract
Mannich reaction of the title compound 1 with formaldehyde and morpholine, piperidine or piperazine afforded the Mannich bases 3-5 respectively, whereas the indeno[1.2-d]pyrimidines (6-7) were obtained where primary amines were used. Treatment of 2 with formaldehyde gave benz[b]indeno-diazepine (8). The reaction of formaldehyde with 1 was also investigated.
Cyclische Organylarsino-Schwefeldiimide / Cyclic Organylarsino Sulfur Diimides
Authors: Herberhold Max , Guldner Karlheinz 
Published: March 2015

Abstract
The reactions of the bifunctional bis(chloroarsino) compounds MeCH[As(But )Cl]2 and RCH[AsCl2]2 (R = H, Me) with the salt K2SN2 lead to rings and cages containing arsino-substituted sulfur diimide units.
Oxo-und Thiovanadium(V)-Thiolate/Oxo and Thiovanadium(V) Thiolates
Authors: Preuss Fritz , Noichl Harald 
Published: March 2015

Abstract
Syntheses of oxovanadium(V) thiolates such as O = V(SR)3 (R = tC4H9 , SiPh3 ) and O=V(OtC4H9 )n(StC4H9)3-n(n = 1, 2) are described. The thiovanadium(V) compounds S=V(OtC4H9 )3 , S = V(StC4H9)(OtC4H9) 2 and S=V(SSiPh3)3 have been prepared by various methods :substition

using Lawesson reagent, oxidation of V(OtC4H9)4 by sulfur, or disproportionation reaction of VCl4 with LiSSiPh3 ; O = V (OSiR3)3 (R = Me , Ph) undergoes a reaction with Lawesson reagent to yield dithiophosphonate complexes. All compounds obtained are characterized by 1H and 51V NMR spectroscopy; the stability of thiovanadium(V) compounds is discussed. V(StC4H9)4 has been synthesized as a first example of vanadium(IV) thiolates
Zur Kenntnis von KCrF4/On KCrF4
Authors: Kissel Dieter , Hoppe Rudolf 
Published: March 2015

Abstract
KCrF4 has been prepared as yellowish-green single crystals (by heating of KF, CuF2 , CrF3 ; Au-tube, 750 °C, 60d). It crystallizes in the orthorhombic crystal system (Pnma) with: a = 1573.2, b = 743.2, c = 1833.1 pm, Z = 24. The structure shows [Cr3F9F6/2]3--columns along [010], The Madelung Part of Lattice Energie, MAPLE, is calculated and discussed, along with Effective Coordination Numbers, ECoN (via Mean Fictive Ionic Radii, MEFIR). The structure is described using SCHLEGEL-diagrams.
Cyclophan-Metall-Komplexe: Synthese und Kristallstruktur von ([2](l,4)Naphthalino[2]paracyclophan)gallium(I)-tetrabromogallat(III)/Cyclophane Metal Complexes: Synthesis and Crystal Structure of ([2]( 1,4)Naphthalino[2]paracyclophane)gallium(I) Tetrabromogallate(III)
Authors: Schmidbaur H. , Bublak W. , Müller G. 
Published: March 2015

Abstract
The title complex has been prepared from Ga[GaBr4] and [2](1,4)naphthalino[2]paracyclophane in toluene as a solvent, and the crystal structure of this adduct determined by single crystal X-ray diffraction. The structure is composed of dimeric units Ga2[GaBr4]2 , which are crosslinked into sheets through Ga(I)-arene coordination. Both the benzene ring and the substituted ring of the naphthalene system are η6-bonded from the outer side of the cyclophane cage, each to an univalent metal. The benzene and the naphthalene form an interplane angle of 49.3°. The distance to the benzene ring (2.67 Å) is much shorter than the distance to the naphthalene (2.85 Å), suggesting a stronger complexation with the unperturbed π-system of the former. [2.2](l,4)Naphthalinophane forms no adduct with Ga[GaBr4], and with [2](l,5)naphthalino[2]paracyclophane secondary reactions are observed.
Reaktionen von 2,3-Dihydro-1,3-diborolen mit Kalium und Iodmethan. Charakterisierung der Produkte als (C5H5)Co-Komplexe/ Reactions of 2,3-Dihydro-1,3-diboroles with Potassium and Iodomethane. Characterization of the Products as (C5H5)Co Complexes
Authors: Stumpf Klaus , Siebert Walter , Köster Roland , Seidel Günter 
Published: March 2015

Abstract
The reactions between 2,3-dihydro-1,3-diborole derivatives 1 and potassium in tetrahydrofuran yield dark brown solutions. Without elimination of hydrogen, 1.4 to 1.8 moles of potassium are consumed by one mole of 1. Reduced 1 and iodomethane react to give methylated products, identified by GC/MS studies. Complexation with (C5H5)Co(C2H4)2 leads to the cyclopentadienyl-cobalt complexes 2, iso-2, 3, and 4, of which iso-2 is a new cobalt-hydride sandwich. Methylation reactions of the cobalt sandwich anions (2-H)- are reported.
Interaction of Metal Ions with 7-Deaza-8-aza-and 8-Aza-purines Preparation and X-Ray Structural Analysis of Copper(II) Complexes
Authors: Sheldrick W. S. , Bell P. 
Published: March 2015

Abstract
The reaction of 8-aza-and 7-deaza-8-aza-purines with Cu2+ cations in acid solution has been studied. At a pH value of 2, the 8-azaadenine complex [Cu(H2O)4(AAdH)2](NO3)2 (1), which displays Cu-N9 coordination, may be isolated from solution. The reaction of CuCl2 with 8-aza-hypoxanthine in concentrated HCl solution leads to ring opening at C2 of the azapurine with subsequent formation of dichlorobis[(5-amino-4-carboxamide)[1 - 3]triazole] copper(II) dihydrate 2, in which the triazole ligands display a chelating function, coordinating the metal via N7 and O6. The results for 1 and 2 suggest that copper coordination of the azapurine base is not a prerequisite for opening of the pyrimidine ring. Respectively N9-and N8-coordinated complexes [CUCl3(AllH3)]n 3 and [CuCl2(H2O)(MAllH)]n (4) of allopurinol (AllH2) and 9-methylallopurinol (MAllH) may be prepared by the reaction of CuCl2 with the respective bases in HCl solution. In contrast, with the analogous 1-methyl-4-aminopyrazolo[3,4-d]pyrimidine MAPP, only the salt (MAPPH)4(CU2Cl8) (5) could be isolated under similar conditions, indicating that N8 is less attractive as a binding site in this 7-deaza-8-azaadenine derivative. The structures of 1-5 have been established by X-ray structural analysis. A distorted octahedral [4+2]geometry is found for the copper atoms in 1 and 2. Chlorine bridged polymeric chain structures are adopted by the complexes 3 and 4. An intermediate coordination geometry between trigonal bipyramidal and square-pyramidal is observed for the metal atoms in 3, a distorted square-pyramidal geometry in 4.
Diazoverbindungen, 65 Isomerisierungen im System 4-Diazo-1-buten/2.3-Diazabicyclo[3.1.0]hex-2-en/1.4-Dihydropyridazin/Diazo Compounds, 65 Isomerization Reactions in the System 4-Diazo-1-butene/2.3-Diazabicyclo[3.1.0]hex-2-ene/1.4-Dihydropyridazine
Authors: Heydt Heinrich , Breiner Hans-Werner , Hell Volker , Regitz Manfred 
Published: March 2015

Abstract
(Diazomethyl)diphenylphosphine oxide (2a) adds onto the 1-cyclopropene phosphonates 1a and c under formation of the 2.3-diazabicyclo[3.1.0]hex-2-enes 3a and c. 3a is easily converted into the 1.4-dihydropyridazine 5a. On the other hand the reaction of 1b with 2a directly affords the 1.4-dihydropyridazine 5b. The 2.3-diazabicyclo[3.1.0]hex-2-enes 3a and c isomerize to the allyl diazomethanes 4a and c on heating in benzene. In the case of the reactions 2b+1b as well as 6+1a the direct formation of allyl diazo compounds (4d and 8a respectively) is observed. In a novel reaction 9-diazofluorene (6) yields the 1.3-butadiene 9 when reacted with the cyclo-propene 1b.
Heterocyclische Siebenring-Verbindungen, XXX Synthese und Eigenschaften von 4-Methoxy-1,5-benzothiazepin, einem einfachen Vertreter des 1,4-Thiazepin-Ringsystems/ Heterocyclic Seven-Membered Ring Compounds, XXX Synthesis and Properties of 4-Methoxy-1,5-benzothiazepine, a Simple Derivative of the 1,4-Thiazepine Ring System
Authors: Hofmann Hans , Fischer Herbert 
Published: March 2015

Abstract
Alkylation of 1,5-benzothiazepin-4(5H)-one (1) with dimethyl sulfate and base yields the N-methyl compound 2 whereas with trimethyloxonium fluoroborate the lactimether 3, a simple derivative of the unknown, 1,4-thiazepine is obtained. Compound 3 eliminates sulfur on heating in toluene, yielding 2-methoxy-quinoline. Oxidation of 3 with peracid produces the stable 1,1- dioxide (4).
Reactivity of 1,1-DithioIato Ni(II) and Co(II) with Phenylthiourea, Chlorophenylthiourea and Bis(diphenylphosphinothioyl)methane
Authors: Aly Aref A. M. , Kamal Mostafa M. , El-Meligy Mahmoud S. , El-Said Asma I. 
Published: March 2015

Abstract
The following mixed ligand complexes were synthesized and characterized: Co(Phdtcz)2(Phtu)2, Co(Phdtcz)2(Clphtu)2 , Co(Phdtcz)2(dtm), Ni(Et2dtc)2(dtm), Ni(Phdtc)2(dtm), Ni(p-Toluiddtc)2(dtm), Ni(α-naphdtc)2(dtm), and Ni(Phdtcz)(Et2dtc); where Phdtcz = phenyldithiocarbazate, Et2dtc = diethyldithiocarbamate, Phdtc = phenyldithiocarbamate, p-Toluiddtc = p-toluidinedithiocarbamate, α-naphdtc = α-naphthyldithiocarbamate, Phtu = phenylthiourea, Clphtu - chlorophenylthiourea, and dtm - bis(diphenylphosphinothioyl)-methane. Electronic and IR spectra, magnetic, conductivity and X-ray powder diffraction measurements were carried out. The Ni(II) and Co(II) complexes are suggested to be square planar and octahedral, respectively. The biological activity of the complexes was also tested.
Gasphasen-Reaktionen, 58 [1, 2] β-Chlorethylazid: HCl-Eliminierung und Pyrolyse / Gas Phase Reactions, 58 [1, 2] β-Chloroethyl Azide: HCl Elimination and Pyrolysis
Authors: Bock Hans , Dammel Ralph 
Published: March 2015

The HCl elimination from β-chloroethyl azide (1-azido-2-chloroethane) over potassium tert. butanolate at 350 K in a low pressure flow system is optimized using PE spectroscopic real-time gas analysis. The highly explosive vinyl azide formed can be purified by cool-trapping the by-products. Its subsequent and virtually hazard-free pyrolysis yields 2H-azirine, which can be isolated at temperatures below 240 K.
In contrast, the direct pyrolysis of β-chloroethyl azide requires temperatures above 710 K and results in a simultaneous split-off of both HCl and N2, yielding acetonitrile as the main thermolysis product. No intermediates such as β-chloroethanimine or ketenimine are observed, a result which is interpreted in terms of chemical activation
On the Stereochemistry of the Lone-Pair Electrons in AX6E-Systems: Dynamically Distorted Anion in (NH4)2SeBr6, Statically Distorted Anion in 1,3-Propanediammonium-Hexabromoselenate(IV) (C3N2H12)SeBr6
Authors: Abriel Walter 
Published: March 2015

Abstract
Using 293 K diffractometer intensity data, the crystal structures of (NH4)2SeBr6 (1) and [H3N(CH2)3NH3]SeBr6 (2) have been determined by single crystal X-ray technique and refined to a final Rw of 0.049 and 0.040, respectively. The dark red crystals of 1 are cubic (space group Fm3m) with a = 10.478(2) Å and Z = 4. This structure contains SeBe6
2- octahedra (point symmetry m3̄m, distance Se-Br: 2.577(2) Å in an antifluorite type arrangement of cations and anions. In contrast, the SeBr fi 2-ion in 2 is statically distorted (approximate point symmetry 3m, distance Se-Br min. 2,547(2), max. 2.595(2) Å. The dark red crystals are orthorhombic (space group Pnma) with a = 17.795(3), b = 7.5037(6), c = 10.476(1) Å and Z = 4. The results agree with the rules for the appearance of a static/dynamic stereochemical effect of the lone pair electrons given for TeX6
2- (X = Cl, Br, I) species (W. Abriel, Acta Crystallogr. B 42, 449 (1986)). Consequently these rules can be extended considering SeX6
2- as well. Basic structural data for all compounds containing AX6
2- ions (A = Se, Te; X = Cl, Br, I) known to date are given including the ⊿-values (R. D. Shannon, Acta Crystallogr. A 32, 751 (1976)) as a measure for the distortion of the octahedral anion.
Examination of a New Cross-Linker in Monoclonal Antibody Reaction Against the C-Terminus of Tobacco Mosaic Virus Coat Protein
Authors: Dietzgen Ralf G. , Sander Evamarie , Christner Jürgen , Jung Günther 
Published: March 2015

The C-terminal tetrapeptide Gly-Pro-Ala-Thr of TMV coat protein was linked to poly- (L-lysine) of 37,300 and 80,000 daltons and to human serum albumin using different ratios of tetrapeptide to carrier. The new hydrazidosuccinyl HSc cross-linker effected the specific amino terminal attachment of the tetrapeptide by azide coupling. The synthetic peptide and its conjugates were controlled by various methods including 13C NMR and CD. Using a conjugate containing 74 tetrapeptide residues linked to poly(L-lysine) of 80,000 daltons for screening of monoclonal antibody by ELISA, 5.8 fmol of peptide were detectable.
The serological and biological properties of the monoclonal antibody were assayed by indirect ELISA and by quantitative determination of virus neutralization. This neutralization could be reversed by the poly(L-lysine)-tetrapeptide conjugate but not by the free tetrapeptide.
Darstellung und Eigenschaften von und Reaktionen mit metallhaltigen Heterocyclen, LVII [1]. Stabilisierung der RPSR′-Gruppe in der Koordinationssphäre von Carbonylmangan-Komplexen / Preparation and Properties of, and Reactions with Metal-Containing Heterocycles, LVII [1]. Stabilization of the RPSR′ Group in the Coordination Sphere of Carbonylmanganese Complexes
Authors: Lindner Ekkehard , Auch Konrad , Hiller Wolfgang , Fawzi Riad 
Published: March 2015

Abstract
Stabilization of RPSR′, Manganese Complexes, X-Ray Stabilization of a RPSR′ function is possible by its incorporation into the mono-and binuclear manganese complexes, t-BuP[Mn(CO)5]SPh (3b) and (μ-CH3PSPh)(μ-SPh)Mn2(CO)8 (4a), re-spectively. Formation of 4a is accomplished via the precursors 3a and PhSMn(CO)5 (5), which are both unstable. 3a, b and 5 are formed by reaction of RP(Cl)SPh (la, b) [R = CH3 (a), t-Bu (b)] with [Mn(CO)5]- (2). 4a crystallizes in the orthorhombic space group Pbca with Z = 8.
The Interaction of Copper(II) Ions with the Thyrotropin-Releasing Hormone Synthesized by Adpoc Protection
Authors: Maskos Karol , Kaibacher Hubert , Stock Wieland , Voelter Wolfgang 
Published: March 2015

Abstract
Thyrotropin-Releasing Hormone (TRH), Copper(II) Ion Complexes The copper(II) complexes of the thyrotropin-releasing hormone (L-pyroglutamyl-L-histidyl-L-prolinamide, TRH) in 3 M LiCl-water solutions were investigated as a function of pH by circular dichroism, absorption, and electron spin resonance spectroscopy. It was concluded that a simple ML (IN) complex of copper(II)-TRH is formed over the pH range 4.0-4.5, while 2N and 3N complexes are present in the solutions of pH 4.4-6.0. From pH 6.1 to 9.8 an ML2 (4N) complex is formed and this species is the only complex found over the pH range 6.5-8.5. At pH values above 9.0 a 3N species is formed in addition to a 2N complex which is present in the solutions of pH 11.3. These observations are controversial to former reports.
TRH [1-2] was synthesized using the fully Adpoc (adamantyl-isopropyloxycarbonyl)-protected histidine. From the synthesis the advantages of the Adpoc group, cleavable under extreme mild acidolytic conditions, become obvious.
Studies on the Peptide Alkaloids of Discaria febrifuga
Authors: Voelter Wolfgang , Morel Ademir Farias , Atta-ur-Rahman  , Qureshi Muhammad Munawer 
Published: March 2015

Abstract
A new tryptophan-containing peptide alkaloid, “discarin-K”, has been isolated from Discaria febrifuga, a shrub growing in Brazil, Argentina and Uruguay. Its structure has been determined as 1 on the basis of spectral studies. Another peptide alkaloid, franganin, was also isolated from the same plant and its 1H NMR and 13C NMR have been studied using COSY-45, 2 D-J resolved and DEPT techniques.
Acylierungsreaktionen an Enaminen / Acylation Reactions of Enamines
Authors: Möhrle Hans , Dwuletzki Heinz 
Published: March 2015

Abstract
The ratio of isomeric enaminones, obtained by acylation of enamines with acid chlorides in the presence of triethylamine, depends on the possibility of forming isomeric enoles of the inter-mediate cyclobutanone adducts.
Efficient Syntheses of a New Class of 6-Amino-6-deoxy Sugars
Authors: Malik Abdul , Ahmed Zaheer , Kazmi Najam-ul-Hussain , Khan Abdul Qasim 
Published: March 2015

Abstract
Amino Sugars, Triflate Displacement, Amino Acids Novel one step syntheses of a new class of phar-macologically interesting 6-amino-6-deoxy sugars are described. The reaction sequence consists of esterifying 1,2:3,4-di-O-isopropylidene-α-D-galac-topyranose with trifluoromethanesulfonic anhydride and reacting the resulting triflate with a variety of suitably protected naturally occurring amino acids. The difficulties which, sometime, are encountered during displacement reactions in carbohydrates are absent.
Stickstoffverbindungen von Elementen der dritten Hauptgruppe mit intra- und intermolekularen Donor-Akzeptor-Bindungen, III [1]. Dynamische Phänomene und Lewis-Säure-Stärke / Nitrogen Compounds of Elements of the Third Main Group with Intra- and Intermolecular Donor Acceptor Bonds, III [1]. Dynamic Phenomena and Lewis Acidity
Authors: Veith M. , Belo A. 
Published: March 2015

Abstract
Compounds of the general formula tBuN(H)-SiMe2 -N(tBu)ElX2 (El = B, X = Me (1m), F (1f), Cl (1c); El = AI, X = Me (2m), Cl (2c), Br (2b); El = Ga, X = Me (3m), Cl (3c), Br (3b); El = In, X = Me (4m), Cl (4c), Br (4b); El = Tl, X = Me (5m)) and tBuN(D)-SiMe2-N(tBu)ElMe2 (El = Al (2d), Ga (3d), In (4d)) have been characterized by IR and temperature dependent 1H NMR techniques with respect to their structural changes in solution. A reversible, dynamic, intramolecular equilibrium between two enantiomeric four-membered rings has been established to be responsible for the changes in the spectra. The cyclic form B1, which arises from Lewis acid base interaction of the tert-butyl-amino with the ElX2 group, transforms to the mirror-image B2 via an acyclic intermediate, in which reorientation of the groups by rotation or inversion can take place. In the boron derivatives (1m, 1c, and 1f) no comparable N-B interaction can be detected. The Lewis acidity of the ElX2 group deduced from NH wave numbers increases within the following series: TlMe2<GaMe2≈InMe2<AlMe2<GaBr2≈InBr2<GaCl2≈AlBr2≈InCl2<AlCl2. Intramolecular hydrogen transfer from one nitrogen atom to the other can be excluded by comparison of the rate constant kʜ vs. kᴅ. The free enthalpy of activation Δ G* depends on the acidity of E1X2, the steric requirements and the relative masses of X. The syntheses and characterisation of 1f, 2b, 3b, 4b, 2d, 3d, and 4d are described.