An easy stereoselective access to beta,gamma-aziridino alpha-amino ester derivatives via mannich reaction of benzophenone imines of glycine esters with N-sulfonyl alpha-chloroaldimines

Mannich-type addition of benzophenone imine glycinates across newly synthesized N-(p-toluenesulfonyl) alpha-chloroaldimines afforded gamma-chloro-alpha,beta-diamino ester derivatives with moderate diastereoselectivity as separable mixtures of anti and syn diastereomers. The gamma-chloro-alpha,beta-diamino esters were efficiently cyclized under basic conditions to the corresponding beta,gamma-aziridino alpha-amino ester derivatives, representing a new class of conformationally constrained heterocyclic alpha,beta-diamino acid derivatives. The relative configuration of the aziridines was determined via X-ray diffraction analysis. Mechanisms and intermediate transition states to explain the stereochemical outcome of the Mannich reaction with different substrates or under different conditions are proposed. The synthetic importance of the beta,gamma-aziridino alpha-amino ester derivatives is demonstrated by their conversion into the corresponding Boc-protected derivatives and ring opening reactions to alpha,beta-diamino esters and a gamma-amino alpha,beta-unsaturated amino ester.     

"Water-stable boron-iodinated dicarbollide dianions [7,8-nido-C2H2B9I9]2- and [7,8-nido-C2H2B9I8H]2-"

The reaction of 3,4,5,7,8,9,10,11,12-I(9)-1,2-closo-C(2)B(10)H(3) with KOH/EtOH gave a mixture of the boron periodinated [1,2,3,4,5,6,9,10,11-I(9)-7,8-nido-C(2)B(9)H(2)](2-) and the highly iodinated on boron [1,2,4,5,6,9,10,11-I(8)-7,8-nido-C(2)B(9)H(3)](2-) in approximately 50% each. Moreover, 3,4,5,6,7,8,9,10,11,12-I(10)-1,2-closo-C(2)B(10)H(2) was reacted with KOH/EtOH to purely produce [1,2,3,4,5,6,9,10,11-I(9)-7,8-nido-C(2)B(9)H(2)](2-). It is the first dinegative dicarbollide stable in water or protic solvent reported in literature.     

Why betaine crystallizes in high local Cs symmetry. An ab initio MO and DFT study of anhydrous betaine and betaine monohydrate

A theoretical study of the structure, charge distribution, rotational barrier and fundamental vibrations of anhydrous betaine (CH₃)₃NCH₂COO (trimethylglycine) was carried out and compared with available experimental data. Calculations were carried out at HF, MP2 and B3LYP levels using a 6-31+G(d,p) basis set. The calculated rotational barrier of the betaine carboxylic group is 40.5 kJ/mol at the MP4(SDQ)/6-311G(d,p)//HF/6-31+G(d,p) level of theory. The rotation of the carboxylic group changes the molecule from a highly symmetric (C _s ) conformation into a twisted conformation resulting in shortening of the molecule by about 50 pm. Natural population analysis (NPA) indicates intramolecular interaction between the carboxylic oxygen and the nearest methyl hydrogens resulting in internal hydrogen bonding. MP4(SDQ)/6-311G(d,p) single-point NPA calculations on a betaine monohydrate model taken from the X-ray geometry show an expected weakening in the internal hydrogen bond. Calculations explain why betaine preferentially crystallizes in high local C _s symmetry. Received: 24 March 1998 / Accepted: 3 September 1998 / Published online: 7 December 1998     

Adduct formed by chromium trioxide and zwitterionic quinolinic acid

Chromium trioxide forms an adduct with zwitterionic quinolinic acid. The structure of the product was found to be (quinolinium-3-carboxylato-O)trioxidochromium(VI), determined by single-crystal X-ray diffraction methods. To evaluate the bonding properties of the compound, its structure was optimized at the B3LYP/6-311G* level of theory. The electronic characteristics were investigated by topological methods applied to the total charge density in various model compounds including the title compound, title compound with a HF molecule presenting a hydrogen bonding and anionic moiety. Calculated aromaticity indices indicate that the quinolinic rings tend to conserve their degree of aromaticity against hydrogen bonding. However, when there is hydrogen bonding involving an N-H bond or when the quinolinium zwitterion is deprotonated, there are clear changes in the interaction between chromium trioxide and the quinolinic moiety.      

Synthesis of conformationally restricted 1,2,3-triazole-substituted ethyl β- and γ-aminocyclopentanecarboxylate stereoisomers. Multifunctionalized alicyclic amino esters

Stereoisomers of 1,2,3-triazole-functionalized, conformationally restricted β- or γ-amino esters with a cyclopentane skeleton were efficiently synthetized from the bicyclic β-lactam 6-azabicyclo[3.2.0]hept-3-en-7-one (1) and Vince γ-lactam (15) in five or six steps involving the azide-alkyne 1,3-dipolar cycloaddition of azido-substituted amino ester stereoisomers with nonsymmetric acetylenes. The azide-alkyne click reactions were investigated under thermal and Cu(I)-catalyzed conditions. Surprisingly, the thermally induced cycloaddition furnished the corresponding 1,4-triazoles regioselectively, which also took place selectively in response to Cu(I) catalysis.     

Synthesis of conformationally constrained tricyclic <Emphasis Type="Italic">β</Emphasis>-lactam enantiomers through Ugi four-center three-component reactions of a monoterpene-based <Emphasis Type="Italic">β</Emphasis>-amino acid

(1R,2R,3S,4R)-2-Amino-6,6-dimethylbicyclo[3.1.1]heptane-3-carboxylic acid 1 was reacted with three aldehydes and two isocyanides in methanol, in water, and under solvent-free conditions to prepare enantiomeric β-lactams via U-4C-3CRs. The yields in methanol were found to be from acceptable to good. High diastereoselectivities of the reactions were observed, and the diastereoisomers were successfully separated in most cases. In water or under solvent-free conditions, the yields were similar to those in methanol when the aldehyde was pivalaldehyde or propionaldehyde. The advantages of water are the facile isolation of the precipitated product and the shorter reaction time.     

What nonlinear-IR experiments can tell you about water that the IR spectrum cannot

Frequently, the IR spectrum of water is used to characterize the structure and strength of the associated hydrogen bond network. Here, we use nonlinear-IR spectroscopy to investigate the dynamics of four aqueous systems that have very similar absorption spectra. We address the question: to what extent can the dynamics of water vary in systems with very similar absorption spectra? The results illustrate that the vibrational lifetimes and orientational relaxation time scales vary dramatically between the four samples and do not correlate with the amount of water relative to surfactant or solute in solution. Nonlinear-IR spectroscopies are therefore important for providing detailed information necessary to understand hydrogen bonded systems.     

Color tuning of a nickel complex with a novel N2S2 pyridine-containing macrocyclic ligand

The novel pyridine-containing 14-membered macrocycle 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L), which contains an N2S2 donor set, was synthesized, and its protonation behavior was studied by absorption titration with CH3SO3H. The reaction of L with Pd(II) was studied spectroscopically, and the square-planar complex [Pd(L)](BF4) was isolated and characterized. The reactions between L and NiX2 x 6 H2O (X = BF4, ClO4) in ethanol or acetonitrile afforded the octahedral complexes [Ni(CH3CN)(H2O)(L)](X)2 and [Ni(H2O)2(L)](X)2, respectively. The square-planar complexes [Ni(L)](X)2 were obtained by heating these octahedral complexes. Spectrophotometric titrations of [Ni(L)](BF4)2 were performed with neutral and negatively charged ligands. The color of nitromethane solutions of this square-planar complex turns from red to cyan, purple, blue, yellow-green, and pink following addition of halides, acetonitrile, water, pyridine, and 2,2'-bipyridine, respectively. X-ray structural analyses were carried out on the {[Ni(ClO4)(H2O)(L)][Ni(H2O)2(L)]}(ClO4)3, [Ni(CH3CN)(H2O)(L)](ClO4)2, [{Ni(L)}2(mu-Cl)2](ClO4)2, and [{Ni(L)}2(mu-Br)2]Br2 x 2 CH3NO2 complexes.     

Bis(5‐tert‐butyl‐2‐hydroxy‐3‐methylbenzyl)(6‐hydroxyhexyl)ammonium chloride monohydrate,an anion receptor complex

In the title compound, C₃₀H₄₈NO₃⁺·Cl⁻·H₂O, the cation acts with a water molecule as a chloride ion receptor. The chloride ion forms three strong intramolecular hydrogen bonds. The water molecule forms both an intramolecular bridge between one phenol H atom and the chloride ion, and an intermolecular link to the aliphatic alcohol O atom. Weak intermolecular C—H...Cl and C—H ...O hydrogen bonds provide additional packing interactions.     

Syntheses and X-ray crystal structures of alpha- and beta-[XeO2F][SbF6], [XeO2F][AsF6], [FO2XeFXeO2F][AsF6], and [XeF5][SbF6)].XeOF4 and computational studies of the XeO2F+ and FO2XeFXeO2F+ cations and related species

Reactions of XeO2F2 with the strong fluoride ion acceptors, AsF5 and SbF5, in anhydrous HF solvent give rise to alpha- and beta-[XeO2F][SbF6], [XeO2F][AsF6], and [FO2XeFXeO2F][AsF6]. The crystal structures of alpha-[XeO2F][SbF6] and [XeO2F][AsF6] consist of trigonal-pyramidal XeO2F+ cations, which are consistent with an AXY2E VSEPR arrangement, and distorted octahedral MF6- (M = As, Sb) anions. The beta-phase of [XeO2F][SbF6] is a tetramer in which the xenon atoms of four XeO2F+ cations and the antimony atoms of four SbF6- anions are positioned at alternate corners of a cube. The FO2XeFXeO2F+ cations of [FO(2)XeFXeO2F][AsF6] are comprised of two XeO2F units that are bridged by a fluorine atom, providing a bent Xe- - -F- - -Xe arrangement. The angle subtended by the bridging fluorine atom, a xenon atom, and the terminal fluorine atom of the XeO2F group is bent toward the valence electron lone-pair domain on xenon, so that each F- - -XeO2F moiety resembles the AX(2)Y(2)E arrangement and geometry of the parent XeO2F2 molecule. Reaction of XeF6 with [H3O][SbF6] in a 1:2 molar ratio in anhydrous HF predominantly yielded [XeF5][SbF6].XeOF4 as well as [XeO2F][Sb2F11]. The crystal structure of the former salt was also determined. The energy-minimized, gas-phase MP2 geometries for the XeO2F+ and FO2XeFXeO2F+ cations are compared with the experimental and calculated geometries of the related species IO2F, TeO2F-, XeO2(OTeF5)+, XeO2F2, and XeO2(OTeF5)2. The bonding in these species has been described by natural bond orbital and electron localization function analyses. The standard enthalpies and Gibbs free energies for reactions leading to XeO2F+ and FO2XeFXeO2F+ salts from MF5 (M = As, Sb) and XeO2F2 were obtained from Born-Haber cycles and are mildly exothermic and positive, respectively. When the reactions are carried out in anhydrous HF at low temperatures, the salts are readily formed and crystallized from the reaction medium. With the exception of [XeO2F][AsF6], the XeO2F+ and FO2XeFXeO2F+ salts are kinetically stable toward dissociation to XeO2F2 and MF5 at room temperature. The salt, [XeO2F][AsF6], readily dissociates to [FO2XeFXeO2F][AsF6] and AsF5 under dynamic vacuum at 0 degree C. The decompositions of XeO2F+ salts to the corresponding XeF+ salts and O2 are exothermic and spontaneous but slow at room temperature.