Synthesis of large chelate rings with diphosphites built on a cyclodextrin scaffold. Unexpected formation of 1,2-phenylene-capped α-cyclodextrins

Two primary face difunctionalised α-cyclodextrins (α-CDs) bearing AC and AD-positioned triarylphosphite ligands have been synthesised and their ability to form large chelate rings has been evaluated. 6^A,6^D-Bis-O-{2-〚(diphenoxyphosphino)oxy〛phenyl}-2^A,2^B,2^C,2^D,2^E,2^F,3^A,3^B,3^C,3^D,3^E,3^F,6^B,6^C,6^E,6^F-hexadeca-O-methyl-α-cyclodextrin (L1) was prepared in three steps in 59% overall yield: (i) treatment of 6^A,6^D-di-O-(methylsulfonyl)-2^A,2^B,2^C,2^D,2^E,2^F,3^A,3^B,3^C,3^D,3^E,3^F,6^B,6^C,6^E,6^F-hexadeca-O-methyl-α-cyclodextrin (1a) with sodium 2-(benzyloxy)phenolate, affording a mixture of the corresponding bisaryloxy substitution product 2a; (ii) cleavage of the benzyl groups of 2a with formation of bisphenol 6a; (iii) reaction of 2a with chlorodiphenylphosphite to afford L1. Diphosphite L2 was obtained in a similar manner using the AC dimesylate 1b (yield: 54%). In step (i) of each synthesis, the unexpected formation of a catecholato-capped CD was observed as a result of benzyl loss under the used arylation conditions. The AD-bridged product was characterised by a single crystal X-ray diffraction study. In the solid state, the CD torus adopts the usual circular shape while four glucose rings, although not distorted, are considerably tilted towards the cavity axis. Both ligands, L1 and L2, when reacted with the cationic complexes AgBF₄ or 〚Rh(norbornadiene)(THF)₂〛X (X = BF₄, PF₆), produced selectively chelate complexes having up to 29-membered metallomacrocycles in high yields. Rhodium systems based on either L1 or L2 catalyse effectively the hyfroformylation of 1-octene (TOF up to 1200 mol mol^–1 of Rh h^–1). Hydrogenation of dimethyl itaconate with a Rh(I)/L2 complex produced dimethyl (R)-(+)-methylsuccinate with an EE as high as 83.6%.     

Conformational study of α-arylethylamides of (−)-camphanic acid

The absolute conformation and configuration of diastereomeric amides (4A,B–6A,B) of (1S,3R)-camphanic acid (lactone of 1-hydroxy-2,2,3-trimethylcyclopentan-1,3-dicarboxylic acid, (−)-camphanic acid 9) with α-arylethylamines 1–3 are deduced from ¹H NMR data and MM2 calculations. The α-arylethyl group in diastereomers A and B adopt nearly opposite absolute conformations, stabilized by hydrogen bonding in the syn-oriented O–C(1)–C(6)–N–H unit, and repulsive interaction between the 1′C–Me group and the amide CO group. The absolute configuration (1′S) is assigned to the 4A–6A diastereomers, and the (1′R)-configuration to the 4B–6B diastereomers; this assignment is confirmed by the preparation of 4A and 5A from enantiomerically pure (1′S)-α-arylethylamines 1 and 2, respectively. These results also enabled the assignment of pro-R (H_R) and pro-S (H_S) protons in the benzyl derivative 7.     

Cathodic behaviour of [*η-C3H5)Pd(Ph2P-C2H4-PPh2)] in acetonitrile solution: an electrochemical process involving very fast consecutive chemical reactions

The cathodic reduction of [(η³-C₃H₅)Pd(Ph₂P-C₂H₄-PPh₂)]⁺, A, in acetonitrile solution affords Pd(Ph₂P-C₂H₄-PPh₂)₂, B, and Pd(η³-C₃H₅)₂, C. Its cyclic voltammetric behaviour is studied as a function of scan rate and concentration of A. These results and relevant coulometric experiments indicate a primary reversible charge transfer reaction followed by a fast second order process producing P₁ and P₂. This picture is complicated by a subsequent reaction of B with A leading to a dimeric electroactive species which is reduced at a slightly more negative potential value than A. The rate constants of individual chemical reactions were evaluated by digital simulation and best fit with experimental results.     

Enantiopure isoplagiochin C by directed deracemization through axis-to-axis chirality transfer

Isoplagiochin C 1 was prepared for the first time in enantiopure form from synthetic racemic material, using a novel stereochemical concept. This macrocyclic bisbibenzyl contains two biaryl axes. Of these, axis A is configurationally stable by its fixation within the macrocyclic framework, while axis B is stereochemically unstable. By diesterification of rac-1 with enantiopure (P)-1,1′-binaphthyl-2,2′-dicarboxylic acid, axis B is locked in its P-configuration, thus allowing the resolution and separate saponification of dilactones (P_A,P_B,P)-3 and (M_A,P_B,P)-3 to give the pure enantiomers of 1. This concept permits recycling of any undesired enantiomer of 1 by thermal equilibration of the respective diastereomer of 3.     

Asymmetric nitrogen−35 : Structure and properties of l(s)-α-carboxyethyl-3, 3-bis(trifluoromethyl)diaziridine and its derivatives

A second-kind asymmetric transformation involving N-atom inversion has been observed at 20° for 1(S) - α - carboxyethyl - 3,3 - bis(trifluoromethyl)diaziridine 1 and its methyl ester 2. X-Ray data for the diastereomer (1S, 2S, α-S), 1A (which is thermodynamically preferred in the crystalline phase), ¹H NMR spectra of ethyl ester 3-¹⁵N(1) and 3-¹⁵N(2), CD spectra of 1A,B, 2A,B, potassium salt 4A,B and semiempirical calculations (MINDO/3 and INDO) for 1A, show that the stereospecificity of crystallization of the diastereomer A is due to the higher energy of the crystal lattice of the diastereomer (1R, 2R, α-S), 1B because of hindered charge compensation as well as to the hindrance by the CF₃, groups to intermolecular H-bonds. According to semiempirical calculations, the stability of 3,3 - bis(trifluoromethyl) - diaziridines (TFD) to the action ofel w-orbital energies and depolarization of the C-N bonds due to hyperconjugation and the inductive effect of the CF₃,-groups. The steric effect of these groups is the reason of the low configurational stability of TFD compared with the 3,3-dimethyl analogues.     

Multiphoton ionisation spectroscopy of H2S: a reinvestigation of the 1B1-1A1 band at 139.1 nm

The 3 + 1 multiphoton ionisation (MPI) spectrum of the ¹B₁-¹A₁ transition in H₂S at 139.1 nm has been recorded in both linearly and circularly polarised light. The rotational structure shows marked differences from that of the one-photon absorption spectrum. Properties of the excited state revealed through analysis of this structure include confirmation of its ¹B₁ character, refined values for its A, B and C rotational constants and the operation of an energy-dependent predissociation mechanism. It is shown that the third-rank tensor component of the transition operator dominates over the first-rank component in this MPI band. The orbital nature of this ¹B₁ excited state is considered.     

Laser-induced fluorescence of benzyl radicals in the gas phase

The excitation spectrum of the laser-induced fluorescence of benzyl has been observed in the gas phase. Fluorescence lifetimes of 880 ± 10 ns at zero pressure were obtained for the s, t and 6a¹₀ bands of the (1 ²A₂—1 ²B₂, 2 ²B₂—1 ²B₂) transitions of benzyl-h₇. The fluorescence lifetime of the t band in the corresponding transition of benzyl-d₇ was 1340 ns.     

Magnetic circular dichroism and molecular orbital studies on bicyclo[6,2,0] decapentaene

The magnetic circular dichroism (MCD) spectrum of bicyclo[6,2,0] decapentaene has revealed four skeletal π → π^* electronic transitions in the visible and ultraviolet region. The four MCD bands are assigned to the B₂ ← A₁, A₁ ← A₁. B₂ ← A₁ and A₁ ← A₁ electronic transitions in increasing order of energy.     

Aminyloxide—XVIII : ESR-spektroskopische untersuchung der tautomerie beim “hydrolyseprodukt des porphyrexids”

The hydrolysis of porphyrexine 2a yields 3a not 1a, as was shown by means of the ¹⁵N-labelled compound 2c. Analysis of the ESR spectra of radicals 4 derived from 3 shows that in dimethylsulfoxide these radicals exist in the tautomeric form B whereas in dioxan they exist in form A. The stabilization of form B in dimethylsulfoxide is shown to be due to a specific effect of the solvent.     

Aromatic polyketide glycosides from an entomopathogenic fungus,Cordyceps indigotica

A new aromatic polyketide glycoside, indigotide A (1), was isolated from the culture broth of the entomopathogenic fungus, Cordyceps indigotica, along with known cyclic depsipeptides, destruxins A, A₂, B, B₂ and E (3–7), and a polyketide, NG-393 (8). Repeated treatment of the C. indigotica culture broth with 5-azacytidine, a DNA methyltransferase inhibitor, led to the isolation of another new aromatic polyketide glycoside, indigotide B (2).     

Structures and bonding situation of Pb2X2 (X?=?H, F, Cl, Br and I)

Quantum chemical calculations using DFT (BP86) and ab initio methods (MP2, MP4 and CCSD(T)) have been carried out for the title compounds. The nature of the Pb?CPb interactions has been investigated with an energy decomposition analysis. The energy minimum structures of the halogen substituted Pb₂X₂ molecules possess a doubly bridged butterfly geometry A like the parent system Pb₂H₂. The unusual geometry can be explained with the interactions between PbX fragments in the X ²?? ground state which leads to one Pb?CPb electron-sharing ?? bond and two donor?Cacceptor bonds between the Pb?CX bonds as donor and vacant p(??) AOs of Pb. The energy difference between the equilibrium form A and the linear structure XPb??PbX (E) which is a second-order saddle point is much higher when X is a halogen atom than for X?=?H. This is because the a ⁴??^?????X ²?? excitation energies of PbX (X?=?F?CI) are higher than for PbH. The structural isomers B, D1, D2, E, F1, F2 and G of Pb₂X₂ are no minima on the potential energy surface.     

DBU induced formation of 8-bromoguanosine dimer with three hydrogen bonds between the GG− base pairs

Upon hemideprotonation of 8-bromoguanosine (8-BrG) at the N1 position, induced by DBU, the adduct [8-BrG][8-BrG]^?[DBU–H]⁺ was formed. Slow evaporation of the 8-BrG methanol solution, in the presence of 0.5 equiv of DBU, yielded two polymorphic structures (1 and 2), where a neutral [8-BrG] (A) and N1 deprotonated, anionic 8-bromoguanosine [8-BrG]^? (B) were joined together through three intermolecular hydrogen bonds involving O6, N1 and C2–NH₂ sites. Such pairing gave planar GG^? dimers as the basic motif of crystal packing in both polymorphs. Both neutral and deprotonated guanosine molecules in the structure of 1 had the ribose units in a syn conformation. In the structure of polymorph 2, the N1 deprotonated guanosine molecule (B) retained the syn glycosidic conformation, while the non-deprotonated guanosine molecule (A) adopted the natural anti conformation of the ribose unit with respect to the nucleobase. Ribose rings revealed different puckering; only those of deprotonated molecules 1B and 2B possessed the usual C2′-endo envelope conformation. Crystal packing in both structures was guided by the highly complex H-bonded pattern. The CSD was searched for related structures, which are discussed with reference to polymorphs 1 and 2. ¹H and ¹³C NMR spectroscopic evidence is provided showing that the three H-bonded adduct [8-BrG][8-BrG]^?[DBU–H]⁺ was also formed in the highly H-bond competitive DMSO solution.     

Structure and Chemical Bonding of the B<Subscript>3</Subscript>S<Stack><Subscript>n</Subscript><Superscript>0/−</Superscript></Stack> (<Emphasis Type="Italic">n</Emphasis> = 2–4) Boron Sulfide Clusters: A Density Functional Theory Investigation

A density functional theory investigation on the structural and bonding properties of B₃S _n ^?/0 (n = 2–4) series has been performed. Based on B3LYP and CCSD(T) calculations, we present the linear D _∞h B₃S₂ ^? (1, ³Σ_g) and D _∞h B₃S₂ (2, ²Π_u), the Y-shaped C _2v B₃S₃ ^? (3, ¹A₁) and C _2v B₃S₃ (4, ²B₂), and perfectly planar structures C _2v B₃S₄ ^? (5, ¹A₁) and C _2v B₃S₄ (6, ²B₂) that contain rhombic B₂S₂ rings. The 1–6 ground-state structures are planar with linear “B–B–B” core, in which the first and the second S atoms prefer to bond terminally to the terminal B, and the third S atom bonds to the center B, however, when the third S atom is added with the fourth, the atoms tend to be in the bridging positions of two adjacent B atoms. The growth pattern of B₃S _n ^?/0 (n = 2–4) clusters helps to understand the structural properties of the other small boron sulfide clusters. Bonding analyses reveal that a dual or single three-center one-electron (3c–1e) π hypervalent bonds located over the “B–B–B” core of D _∞h B₃S₂ ^? (1) and B₃S₂ (2), respectively. While C _2v B₃S₄ ^? (5) and B₃S₄ (6) with rhombic B₂S₂ rings as the center with –BS and –S units all possess 4c–4e bonds (o-bonds) in the rhombic B₂S₂ rings.     

Further studies on the properties and effect of high energetic ionizing radiation on copper(II) complexes: 1H NMR,electronic absorption,ESR spectra and solid electrical conductivity

The effect of energetic γ-radiation on ¹H NMR, electronic absorption, ESR spectra, differential thermal analysis (DTA) and solid state dc electrical conductivity of the ligand N-phenyl-2-(2-(phenylamino)acetyl)hydrazine carbothioamide (H₂L) and its copper(II) complexes; Cu(HL)(OAc)H₂O, Cu(HL)BrH₂O and Cu(H₂L)₂(NO₃)₂?3H₂O before and after γ-irradiation (hereafter referred to as (B), (B ₁ ), (B ₂ ), (B ₃ ) and (A), (A ₁ ), (A ₂ ), (A ₃ ), respectively) has been studied. Electronic spectral bands of the complexes after irradiation exhibited some better resolved shapes with a remarkably higher absorbance, ESR spectrum of complex Cu(HL)BrH₂O (B ₂ ) before irradiation showed isotropic spectrum with g _iso = 2.075 however, after irradiation (A ₂ ) displayed axial ESR spectrum with g _∥ > g _⊥ > 2.0023 and d _(x2?y2) ground state. DTA of the compounds reveals that γ-irradiation induced generation of new peaks as well as changes in the peak intensities. Solid state dc electrical conductivity for complexes was investigated before and after γ-irradiation. Complexes were found to be semiconductors, the activation energies (E _a) were calculated for the complexes by using the Arrhenius plot.     

Modulation of fluorescence emission of 1-(2-pyridyl) pyrazole derived Schiff base ligands by exploiting their metal ion sensitive binding modes

Dioxomolybdenum(VI) complexes [MoO₂(B¹)H₂O] (1), [MoO₂(B²)EtOH] (2), [MoO₂(B³)EtOH] (3) and [MoO₂(B⁴)EtOH] (4) were synthesized using the Schiff base ligands H₂B¹(previously reported), H₂B², H₂B³ and H₂B⁴, respectively. These ligands were prepared by condensation of 1-(2-pyridyl) 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde, o-hydroxy acetophenone, 5-bromo salicylaldehyde and 5-nitro salicylaldehyde respectively. Due to the presence of a substituted 1-(2-pyridyl) pyrazole unit, ligands H₂B¹, H₂B² and H₂B³ exhibit fluorescent emissions, and the most intense emission was obtained for H₂B³. H₂B⁴ is incapable of showing fluorescence emission. As the ligands are capable of using different binding modes, according to the demands of the guest metal ions, their emission properties also change accordingly. The dioxomolybdenum(VI) complex of the ligand H₂B¹, i.e. complex 1, shows quenched emission compared to H₂B¹. Again when Cu²⁺, Co²⁺ or Ni²⁺ ions are added to a solution of 1, in each case a new complex of Cu²⁺ Co²⁺ or Ni²⁺ is formed in solution and further quenching was observed. However, with Zn²⁺ input to a solution of 1, fluorescence recovery was observed up to the level of the free ligand. The copper(II) complex of H₂B¹ (complex 5), produced by adding equivalent amount of Cu²⁺ salt to a solution of 1, was isolated and characterized. One of the dioxomolybdenum(VI) complexes, 3, when subjected to an oxo-transfer reaction with PPh₃ produces complex [MoO(B³)CH₃CN] (6). Complex 6 shows reduced fluorescence emissions compared to 3 in the solid phase. These observations open up the possibilities for these ligands to work as fluorescent signaling system with different metal ion inputs. All the complexes are characterized by elemental analyses, electronic spectra, IR, ¹H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1 and 5, as well as the ligands H₂B² and H₂B³, have been crystallographically characterized.     

Nucleophilic eliminative ring fission of bridgehead substituted 1,3-bishomocubyl acetates

The base induced cage fission of three different types of functionalized bridgehead substituted 1,3-bishomocubyl acetates, vizA,B and C is described. The synthesis of two 6-functionalized 1,3-bishomocubyl 4-acetates (type A), viz4-acetoxypentacyclo[5.3.0.0^2,5.0^3,9.0^4,8]decan-6-one 5 and its ethylene acetal 6 has been accomplished starting from the readily available Diels-Alder adduct 4. The synthesis of three 1,3-bishomocubyl 8-acetates (type B), viz 8-acetoxypentacyclo[5.3.0^2,5.0^3,9.0^4,8]decan-6-one 15, its ethylene acetal 16 and the parent acetate 20 has been carried out starting from the cyclopentadiene-benzoquinone adduct 7. Base induced homoketonization of 6, 16 and 20 leads regio- and stereospecifically to the thermodynamically favored half cage ketones 22,28 and 31, respectively. In contrast, the cage opening of the β-ketoacetates 5 and 15 is essentially directed by the β-ketone function. In the case of 5, regiospecific cleavage of the central C₄-C₅ bond is observed producing in a stereospecific manner diketone 25 in quantitative yield. Under similar conditions, acetate 15 gives a complex mixture of cage opened products arising from further fragmentation of the initially formed diketone 34. Deuterium labeling experiments reveal an anti-Bredt behavior of half cage ketones 28 and 31. The synthesis of a bridgehead acetate of type C has been accomplished by stereoselective reduction of ketone acetate 5 with LiAlH(t-OBu)₃ followed by mesylation. A mixture of epimers 36a and 36b (ratio 1:4) is obtained from which the predominant anti-epimer 36b could be isolated. An X-ray analysis established its structure. Base induced cage fission of 36b leads regiospecifically to tetracyclo[5.3.0.0^2,5.04,8]decenone 37. In contrast the syn-epimer 36a, under similar conditions, only affords the bridgehead alcohol 38.     

ESR and pH-potentiometric study of the mixed-ligand complex formation in the copper(II)-4-fluorosalicylic acid-N,N-diethylnicotinamide system: Structure and spectral properties of [Cu(4-fluorosalicylate)2(N,N-diethylnicotinamide)2(H2O)2] complex

EPR simulation method together with pH-potentiometry combined with UV-Vis spectrophotometry were used for the study of the ternary system 4-fuorosalicylic acid (HA)-N,N-diethylnicotinamide (B)-copper(II) in aqueous solution. The N,N-diethylnicotinamide ligand is a weak donor, its mixed-ligand complexes with 4-fluorosalicylate anions are more favoured. The number of coordinated N,N-diethylnicotinamide molecules increases with decreasing temperature: up to four ones were detected in the coordination sphere of copper(II) in frozen solutions. The formation of [CuH₋₁AB₂] and [CuH₋₁A] was detected by all methods at neutral pH. At lower pH values, [CuA₂B₂] and [CuB] become dominant, and this fact is in good agreement with [CuA₂B₂(H₂O)₂] crystals obtained from similar solutions. The structural unit of the [CuA₂B₂(H₂O)₂] complex consists of a copper(II) ion, which is monodentately coordinated by a pair of 4-fluorosalicylate anions and by a pair of N,N-diethylnicotinamide in trans positions in the basal plane, and by two water molecules in the axial positions of a tetragonal bipyramid.     

Two-photon (A1B2 ← X1 A1) supersonic jet spectrum of aniline

The supersonic jet multiphoton ionization (2 photons to resonance, 4 to ionization) ¹A ← ¹X spectrum of aniline is reported in the 560–590 nm region. The two-photon ¹A ← ¹X spectrum is very similar to the analogous one-photon spectrum. In particular, ν₁₄, the Kekulé signature mode of two-photon ¹L_b substituted benzene spectra is not prominent, but two quanta of the amino inversion mode, ν_I, are. A dispartiy between theoretical calculations of the ¹A ← ¹X two-photon cross-section, and the thermal lensing cross-section reported by Rice and Anderson [J. phys. Chem. 90, 6793 (1986)] is noted. The theoretical considerations only account for about half the thermal lensing intensity.     

Equilibrium structure and vibrational frequencies of the O4 molecule

SCF closed shell calculations were performed to determine the equilibrium structure and vibrational frequencies of the O₄ molecule by means of Payne's method and with the help of the molecule's symmetry coordinates. The equilibrium geometry corresponds to symmetry group D_2d with R = 1.505 Å and h = 0.094 Å. The vibrational frequencies are: ν₅(E) = 885.5 cm^?1, ν₃(B₁) = 1051.9 cm^?1, ν₁(A₁) = 1018.3 cm^?1, ν₄(B₂) = 880.3 cm^?1. The second vibrational coordinate (A₁) corresponds to a double-well potential. The first vibrational levels were calculated by a variational method.     

Zur umsetzung von trimethylsilyl-methylen-dimethylsulfuran mit carbonylverbindungen : Reaktionen mit organosiliziumverbindungen, 1. mitt.

The first step in the reaction of trimethylsilylmethylene-dimethylsulfurane 1 (prepared from (CH₃)₃SiCH₂S?(CH₃)₂ī with 1 equivalent (CH₃)₃COK) with carbonyl compounds (R¹)(R²)CHCOCH₂R³2 leads Peterson-like way to the non-isolable vinylsulfoniumdimethylsilanolate-intermediate B or its recombined product A. Depending on the reaction conditions and the nature of the substituents R¹, R² and R³ there exist five different pathways to the end products 3–7. Frequently one can find an elimination of trimethylsilanole followed by a 2,3-sigmatropic rearrangement of an allyl-substituted methylene - sulfurane - intermediate to the 2,3,3 - trialkyl - 5 -thiahex -1 - enes 3 [CH₃SCH₂C(R¹)(R²)C(CH₂R³)=CH₂]. Sometimes this formation of 3 is suppressed by means of two equivalents of (CH₃)₃COK. In this case demethylation of the assumed precursor B arises yielding the E,Z-vinylsulfides 4 [CH₃SCH=C(CH₂R³)(CHR¹R²)], whereas the formation of the methylthiomethyl-dialkylcar-binoles 5 [CH₃SCH₂C(OH)(CH₂R³)(CHR¹R²)] can be explained by the demethylation of the precursor A. Treatment with five equivalents of (CH₃)₃COK yields in one case the 2,2,5,7 - tetramethyl - 5 - hydroxy - 3 - oxaoctane (7a) as

a consequence of a extrusion of dimethylsulfide. Frequently also epoxides of type 6 [CH₂-C(CH₂R³)(CHR¹R²)] can be isolated. Their formation is compared with the well-known preparation of epoxides by the dimethylsulfonium-methylide on the one and dimethylsulfoxoniummethylide on the other side.