Suzuki-Miyaura coupling on the three upper rims of hexahomotrioxacalix[3]arenes

The efficient functionalization of three upper rims based on Suzuki-Miyaura coupling to temporarily lower rim-protected hexahomotrioxacalix[3]arenes was developed. After deprotection of the three protecting groups, the three upper rim-functionalized and lower rim-free hexahomotrioxacalix[3]arenes 5a-5m were synthesized.     

Exploitation of sugar ring flipping for a hinge-type tether assisting a [2 + 2] cycloaddition

Methyl 3-O-p-methoxybenzyl-beta-D-xylopyranoside (2) was exploited as a novel hinge-type tether for the [2 + 2] cycloaddition of cinnamate. The major ring conformation occupied by the 2,4-dicinnamate derivative of 2 was 4C1, which extends two cinnamates along a diequatorial orientation. However, 3-O-deprotected dicinnamate 5, when in a non-polar solvent, favours the 1C4 conformation, which assists the approach of two cinnamates with the 1,3-diaxial scaffold. Photoirradiation of compound at 313 nm in CHCl3 afforded the intramolecular cycloaddition of cinnamates to give methyl beta-, delta-, and xi-truxinates in a 86 : 8 : 6 ratio after transesterification with methanol. The regio- and stereoselectivities are comparable to those reported by others for tethered cinnamates. The per-deuterated dicinnamate derivative of 5 facilitated the conformation analyses of the pyranoside rings by 1H NMR, indicating that all the products of photoirradiation had 1C4-fixed pyranosides. Excellent beta-selectivity was achieved when m-bromocinnamate was subjected to hinge-tethered [2 + 2] cycloaddition.     

Ferrocenyl D-π-A conjugated polyenes with 3-dicyanomethylidene-1-indanone and 1,3-bis(dicyanomethylidene)indane acceptor groups: Synthesis, linear and second-order nonlinear optical properties and electrochemistry

Second-order nonlinear optical chromophores incorporating the ferrocenyl group as an electron donor and 3-dicyanomethylidene-1-indanone and 1,3-bis(dicyanomethylidene)indane acceptor groups, connected by a conjugated polyenic bridge of varied length (2[n] and 3[n], respectively) have been synthesized. The electronic absorption spectra of these compounds display in the visible region bands attributable to π-π* and metal-to ligand charge transfer (MLCT) transitions. The energies of these transitions are close to those reported earlier for ferrocenyl D-π-A chromophores with the strongest acceptor groups, e.g., with the 3-dicyanomethylidene-2,3-dihydrobenzothiophene-1,1-dioxide group (1[n]) [V. Alain, M. Blanchard-Desce, C.-T. Chen, S.R. Marder, A. Fort, M. Barzoukas, Synt. Met. 81 (1996) 133]. The solid-state structure of 2[3], determined by X-ray diffraction shows a significant reduction of the bond length alternation (BLA), 0.05 Å, suggesting high first hyperpolarizability. However, a centrosymmetrical packing of molecules of this compound in the crystal excludes its second harmonic generation ability. The μβ values of 2[n] and 3[n], determined by the EFISH technique at 1907 nm are high and increase with the increasing length of the conjugated π-bridge. The highest value of μβ (8720 × 10⁻⁴⁸ esu) was determined for 3[4], which is close to that reported for 1[4] (11 200 × 10⁻⁴⁸ esu), the highest value found for a ferrocenyl D-π-A chromophore until now.     

Total synthesis of radulanin H and proposed structure of radulanin E

The total synthesis of radulanin H and the proposed structure of radulanin E have been achieved utilizing an intramolecular condensation, sequential regioselective C- and O-allylations, and ring closing metathesis as the key steps.     

A nonaqueous potentiometric titration study of the dissociation of t-butyl methacrylate-methacrylic acid copolymers.

The dissociation of t-butyl methacrylate-methacrylic acid copolymers in dimethyl sulfoxide was analyzed by a nonaqueous potentiometric titration technique. The negative logarithm of the dissociation constant of the monomer unit of a methacrylic acid (MAA) monotonously increased with the increasing degree of dissociation corresponding to the titrant/MAA amount ratio, and was highly influenced by the copolymerization ratio. The results are discussed in terms of the suppression of the dissociation of MAA by a neighboring charged methacrylate anion unit.     

Separation of Photoactive Conformers Based on Hindered Diarylethenes: Efficient Modulation in Photocyclization Quantum Yields

Endowing both solvent independency and excellent thermal bistability, the benzobis(thiadiazole)‐bridged diarylethene system provides an efficient approach to realize extremely high photocyclization quantum yields (Φ_o‐c, up to 90.6 %) by both separating completely pure anti‐parallel conformer and suppressing intramolecular charge transfer (ICT).     

Membrane Permeability and Stability of Liposomes Suspended in Shear Flow

The 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposome has been characterized in its stability and membrane permeability to 5(6)-carboxyfluorescein (CF) in the shear flow generated in the cone-and-plate geometry. The CF-containing liposomes (CFLs) were 101–323 nm in the mean diameter D _P as measured with the dynamic light scattering (DLS) method. Adsorption of lipids to the cone-and-plate was observed, which clearly depended on the shear stress applied at the shear rate γ up to 1.5 × 10³ s^?1. The permeability of CFLs with D _P of 101 and 117 nm definitely increased at the maximum γ value where the adsorption was negligible. The permeability coefficient of CF at 40°C in the shear flow was 5.7 times larger than that in the static liquid system. The DLS measurements revealed that the size distribution of CFLs with D _P of 101–189 nm was practically unchanged under the shear stress even at 55°C. The results obtained show that the shear stress can permeabilize the CFL membranes with neither structural collapse nor coalescence.     

Effect of an alkyl substituted in salen ligands on 1,4‐Cis selectivity and molecular weight control in the polymerization of 1,3‐butadiene with (salen)Co(II) complexes in combination with methylaluminoxane

The effect of an alkyl substituted in the aromatic ring of the salen ligand on the polymerization of butadiene (Bd) with (salen)Co(II) complexes in combination with methylaluminoxane (MAO) was investigated. The activity for the polymerization of Bd was influenced significantly by the introduction of alkyl groups at the 3,3′,5,5′‐positions in the aromatic ring of the salen ligand, and both the polymerization rate and 1,4‐cis contents increased in the following order with respect to the alkyl group: H < CH₃ < t‐C₄H₉. This is in good agreement with the bulkiness of the alkyl groups. The activity for the polymerization of the (salen)Co(II) complex possessing t‐C₄H₉ at the 3,3′‐positions was higher than that of the (salen)Co(II) bearing t‐C₄H₉ at the 5,5′‐positions. Thus, the introduction of bulky substituents at the 3,3′‐positions of the salen ligand was an important factor in achieving both high activity and high 1,4‐cis selectivity in the polymerization of Bd with (salen)Co(II) complexes in combination with MAO. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4088–4094, 2006