Hydroamination and hydroalkoxylation catalyzed by triflic acid. Parallels to reactions initiated with metal triflates

Intermolecular additions of the O-H bonds of phenols and alcohols and the N-H bonds of sulfonamides and benzamide to olefins catalyzed by 1 mol % of triflic acid and studies to define the relationship between these reactions and those catalyzed by metal triflates are reported. Cyclization of an alcohol containing pendant monosubstituted and trisubstituted olefins catalyzed by either triflic acid or metal triflates form products from addition to the more substituted olefin, and additions of tosylamide catalyzed by triflic acid or metal triflates form indistinguishable ratios of the two N-alkyl sulfonamides.     

Novel parallel reaction between a [1,5] sigmatropic alkylthio shift and a [1,5] sigmatropic hydrogen shift observed in a 2H-azepine ring

Although heating 2-methoxy-2H-azepine results in a [1,5] sigmatropic hydrogen shift, heating 2-propylthio-2H-azepine results in not only a [1,5] sigmatropic hydrogen shift but also a [1,5] sigmatropic propylthio shift. Kinetic measurements reveal that migratory aptitudes increase in the order of MeO < H, PrS. These [1,5] sigmatropic shifts are discussed on the basis of ab initio DFT calculations. [reaction: see text].     

Structures of tetrafluorocyclopropene, hexafluorocyclobutene, octafluorocyclopentene and related perfluoroalkene radical anions revealed by electron spin resonance spectroscopic and computational studies

Isotropic and anisotropic ESR spectra were observed for the radical anions of hexafluorocyclobutene (c-C(4)F(6)(-)), octafluorocyclopentene (c-C(5)F(8)(-)) and perfluoro-2-butene (CF(3)CF=CFCF(3)(-)) in gamma-irradiated plastically crystalline neopentane, tetramethylsilane (TMS) and TMS-d(12) matrices, or the rigid 2-methyltetrahydrofuran (MTHF) matrix. The isotropic spectra of c-C(4)F(6)(-) and c-C(5)F(8)(-) are characterized by three different sets of pairs of (19)F nuclei with the isotropic hyperfine (hf) splittings of 15.2 (2F), 6.5 (2F), 1.1 (2F) mT for c-C(4)F(6)(-) and 14.7 (2F), 7.4 (2F), 1.0 (2F) mT for c-C(5)F(8)(-). By comparison with the results of ab initio quantum chemical computations, the large triplet (19)F hf splittings of ca. 15 mT are assigned to the two fluorines attached to the C=C bond. The UHF, B3LYP and MP2 computations predict that the geometrical structures of the perfluoroalkenes are strongly distorted by one-electron reduction to form their radical anions; c-C(3)F(4)(-): C(2) symmetry ((2)A state) <-- C(2)(v) ((1)A(1)), c-C(4)F(6)(-): C(1) ((2)A) <-- C(2)(v) ((1)A(1)) and c-C(5)F(8)(-): C(1) ((2)A) <-- C(s) ((1)A'). The structural distortion arises from a mixing of the pi* and higher-lying sigma* orbitals at the C=C carbons similar to that previously found for CF(2)=CF(2)(-) with a C(2)(h) distortion. The isotropic (19)F hf splittings computed with the B3LYP method with 6-311+G(2df,p) basis set for the geometry optimized by the UHF and/or MP2 methods are within 6% error of the experimental values. The experimental anisotropic spectra of c-C(4)F(6)(-), c-C(5)F(8)(-) and CF(2)=CF(2)(-) were satisfactorily reproduced by the ESR spectral simulation method using the computed hf principal values and orientation of (19)F nuclei. In addition, the electronic excitation energies and oscillator strengths for the CF(2)=CF(2)(-), c-C(3)F(4)(-), c-C(4)F(6)(-) and c-C(5)F(8)(-) radical anions were computed for the first time by TD-DFT methods.     

Photocontrolled magnetization of CdS-modified Prussian blue nanoparticles

The first photocontrollable magnetic nanoparticles containing CdS and Prussian blue (PB) have been created using reverse micelles as nanoreactors. Photoinduced electron transfer from CdS to PB in the reverse micelle changed the magnetic properties of the composite nanoparticles from ferromagnetic to paramagnetic. The magnetization in the ferromagnetic region below 4 K was substantially decreased after UV light illumination and could be restored almost to its original level by thermal treatment at room temperature. This novel strategy of designing composite nanoparticles containing photoconductive semiconductors and magnetic materials to create photoswitchable magnetic materials may open many possibilities in the development of magneto-optical devices.     

Chromogenic indicator for anion reporting based on an N-substituted oxoporphyrinogen

5,10,15,20-Tetrakis-3,5-di-tert-butyl-4-oxocyclohexadienylidene porphyrinogen and its di-N-benzylated derivative are solvatochromic dyes capable of binding anionic species. The influence of solvent polarity and hydrogen bonding on their electronic absorption spectra was observed. Hydrogen bonding by the porphyrinogen amine protons of acetone solvent molecules could be observed in the solid state. The acetone solvate of N21N23-dibenzyl-5,10,15,20-tetrakis-3,5-di-tert-butyl-4-oxocyclohexadienylidene porphyrinogen crystallized under anhydrous conditions in the space group P with cell dimensions a = 12.1693(11) A, b = 17.5849(13) A, c = 21.0965(17) A, alpha = 69.870(4) degrees , beta = 78.140(4) degrees , gamma = 82.865(5) degrees . These porphyrinogens are capable of binding a variety of anions and can be used to distinguish fluoride chromogenically from the other halide anions. Solvatochromism was combined with anion binding in an attempt to provide more selective tests for anions. The anion binding properties were investigated using UV/vis spectrophotometry and 1H NMR spectroscopy.     

Self-diffusion of supercritical water in extremely low-density region

The self-diffusion coefficient D for super- and subcritical water is determined by using the proton pulsed-field-gradient spin echo method at high temperatures and low densities. The density of water is ranged in the steamlike region from 0.0041 to 0.0564 g [corrected] cm(-3) at a supercritical temperature of 400 degrees C, also at 0.0041-0.0079 and 0.0041-0.0462 g [corrected] cm(-3) (the steam-branch densities on the coexistence curve and lower) at 200 and 300 degrees C, respectively. The density is precisely determined on the basis of the PVT dependence of the proton chemical shift. The density-diffusivity products in the zero-density limit divided by the square root of the temperature, (rho D)0/square root of T, are 0.94, 1.17, and 1.35 mg m(-1) s(-1) K(-1/2) (mg=10(-3)g) [corrected] at 200, 300, and 400 degrees C, respectively. The (rhoD)0/square root of T obtained decreases with decreasing temperature and is significantly smaller than the temperature-independent value from the hard sphere model, 1.95 mg [corrected] m(-1) s(-1) K(-1/2). The marked temperature dependence reflects the presence of the strong attractive interaction between a pair of water molecules. The magnitude of the experimental D values and the temperature dependence are well reproduced by the molecular dynamics simulation using TIP4P-FQ model. The initial slope of the product rhoD/square root of T against rho is slightly negative at 300 and 400 [corrected] degrees C.     

Synthesis and some properties of binuclear ruthenocenes bridged by oligoynes: formation of bis(cyclopentadienylidene)cumulene diruthenium complexes in the two-electron oxidation

The monoynes [Rc*C[triple bond]CRc*] and [Rc'C[triple bond]CRc'] were obtained in improved yields using [Mo(CO)6]/2-FC6H5OH as a catalyst in the alkyne metathesis of [Rc*C[triple bond]CMe] and [Rc'C[triple bond]CMe], respectively (Rc = ruthenocenyl, Rc* = 1',2',3',4',5'-pentamethylruthenocenyl, and Rc' = 2',3',4',5'-tetramethylruthenocenyl groups). The diynes [Rc*(C[triple bond]C)2Rc*] and [Rc'(C[triple bond]C)2Rc'] were synthesized by the oxidative coupling of the corresponding terminal ethynes in good yields. The triyne [Rc*(C[triple bond]C)3Rc*] and the tetrayne [Rc*(C[triple bond]C)4Rc*] were prepared by the hetero- and homocoupling of [Rc*C[triple bond]CC[triple bond]CH], which was obtained from the reaction of [Rc*C[triple bond]CCHO] with Li[N2CSiMe3], respectively. Although the oxidation waves did not always exhibit a clear two-electron oxidation process, the oxidation potentials shifted to a lower potential with an increase in the number of methyl substituents on the ruthenocenyl ring, and shifted to a higher potential with the increase in the number of C[triple bond]C units; this result is in contrast to that found in the [Rc(CH=CH)(n)Rc] series. The chemical oxidation of [Rc'C[triple bond]CRc'] yielded a stable two-electron-oxidized species, the structure of which was confirmed by X-ray crystallography to be [Ru2(mu2-eta(6):eta(6)-C5Me4C=CC5Me4)(eta-C5H5)2](BF4)2. Changing the substituents (Rc, Rc*, and Rc') had no effect on the chemical oxidation, but in the case of the Rc' series the Me substituent increased the stability of the two-electron-oxidized species in solution. The diyne [Rc*(C[triple bond]C)2Rc*] and the triyne [Rc*(C[triple bond]C)3Rc*] also gave a similar but unstable two-electron-oxidized species. In acetone or acetonitrile, the two-electron-oxidized species of [Rc*C[triple bond]CRc*] and [Rc*(C[triple bond]C)2Rc*] gradually formed the corresponding bis(fulvene)-type complexes. This implies that the two-electron-oxidized species of [Rc*(C[triple bond]C)(n)Rc*] are destabilized with the increasing n.     

Enantioselective total synthesis and stereochemical revision of communiols E and F

The enantioselective total synthesis of candidate structures for communiols E and F, novel bicyclic polyketides of fungal origin, was accomplished using a Lewis acid-mediated ring closure reaction of an allylsilane intermediate as the key step. Comparison of the spectral data of the synthetic materials with those of natural communiols E and F, coupled with biosynthetic considerations, led to the conclusion that the stereochemistry of communiols E and F should be (2S,5S,7R, 8S,11R)- and (5S,7R,8S,11R)-forms, respectively.     

Anti-biofouling properties of polymers with a carboxybetaine moiety

The resistance of random copolymers of BMA and CMB against biofouling was evaluated. The amount of proteins adsorbed onto the CMB copolymers was smaller than that onto other polymers (non-ionic polymers and copolymers of ordinary ionic monomers and BMA) and decreased with an increase in the content of CMB residues. Furthermore, there was a dramatic decrease in the number of cells (platelets and fibroblasts) that adhered to the CMB copolymers compared with that to other polymers. In contrast with this, CMB copolymers were slightly perturbative to both complement and coagulation systems. However, the overall results suggest that zwitterionic moieties are effective for making polymer materials biocompatible due to their excellent anti-biofouling property.     

Photoswitchable Chiral Organocatalysts: Photocontrol of Enantioselective Reactions

This study presents recent advances in photoswitchable chiral organocatalysts and their applications in the photomodulation of enantioselective reactions. Under irradiation with an appropriate wavelength of light, the E/Z-photoisomerization of the photoresponsive units on the catalysts leads to the control of the catalytic activity and/or selectivity of the enantioselective reactions. Additionally, this study elucidates the design, synthesis, and catalytic application of the fabricated azobenzene BINOL-based photoswitchable chiral phase-transfer catalysts. This account will provide insights into the appropriate design of a photoswitchable chiral organocatalyst that can achieve both good enantioselectivity and photocontrol.