Facile Synthesis of 2-Fluorobenzofurans: 5-endo-trig Cyclization of β,β-Difluoro-o-hydroxystyrenes

Efficient synthetic methods were established for obtaining 2-fluorobenzofurans involving various substituents. Upon being treated with 1,8-diazabicyclo[5.4.0]undec-7-ene under microwave irradiation, the α-unsubstituted β,β-difluoro-o-hydroxystyrenes underwent nucleophilic 5-endo-trig cyclization to afford the corresponding 2-fluorobenzofurans in high yields. Furthermore, 2-fluoro-3-iodobenzofuran was successfully synthesized, and its transformation to various 3-substituted 2-fluorobenzofurans was demonstrated.     

Nickel-Catalyzed Reductive Allyl−Aryl Cross-Electrophile Coupling via Allylic C−F Bond Activation

Nickel-catalyzed reductive cross-coupling of allylic difluorides with aryl iodides was achieved via allylic C−F bond activation. Based on this protocol, a series of γ-arylated monofluoroalkenes were synthesized in moderate to high yields with high Z-selectivities. Mechanistic studies suggest that the C−I bonds of the aryl iodides and the C−F bonds of the allylic difluorides were cleaved via oxidative addition and β-fluorine elimination, respectively, where the oxidative addition of less reactive C−F bonds was avoided to permit their transformation.     

Surface segregation in binary mixtures of imidazolium-based ionic liquids

Surface composition of binary mixtures of room-temperature ionic liquids has been investigated using time-of-flight secondary ion mass spectrometry at room temperature over a wide composition range. The imidazolium cations with longer aliphatic groups tend to segregate to the surface, and a bis(trifluoromethanesulfonyl)imide anion (Tf₂N^?) is enriched at the surface relative to hexafluorophosphate (PF₆^?). The surface of an equimolar mixture of Li[Tf₂N] and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) has a nominal composition of [bmim][Tf₂N] because of surface segregation and ligand exchange. The surface segregation of cations and anions is likely to result from alignment of specific ligand-exchanged molecules at the topmost surface layer to exclude more hydrophobic part of the molecules.     

On the wettability of lipid DPPC films

By employing temperature-programmed desorption and time-of-flight secondary ion mass spectroscopy, the adsorption of water on the hydrophilic and hydrophobic surfaces of a lipid (DPPC) film has been investigated. It could be shown that it is possible to prepare lipid films ex situ with a preferential orientation of the lipid molecules on a solid support and to retain their specific properties under ultrahigh vacuum conditions. The water adsorption and desorption kinetics on the hydrophilic and hydrophobic surfaces provided by a lipid film are discussed in terms of their structural and chemical properties.     

Asymmetric (13)C-(13)C polarization transfer under dipolar-assisted rotational resonance in magic-angle spinning NMR

A two-dimensional (2D) homonuclear exchange NMR spectrum in solids often shows an asymmetric cross-peak pattern, which disturbs a quantitative analysis of peak intensities. When magnetization is prepared using cross polarization (CP), the asymmetry can naively be ascribed to nonequilibrium initial magnetization. We show, however, that the CP effect cannot fully explain the observed mixing-time dependence of the peak intensities in 2D (13)C-(13)C exchange spectra of [2,3-(13)C] l-alanine (2,3-Ala) under (13)C-(1)H dipolar-assisted rotational resonance (DARR) recoupling, which has recently been proposed for a broadband recoupling method under magic-angle spinning. We develop a theory to describe polarization transfer in a two-spin system under DARR recoupling. By taking into account the effects of the partial spectral overlap among (13)C signals, which is a unique feature of DARR recoupling, and (1)H-(1)H flip-flop exchange, we can successfully explain the observed mixing-time dependence of the peak intensities of 2D (13)C-(13)C DARR exchange spectra of 2,3-Ala. A simple initial-rate analysis is also examined.     

Evidence of deeply supercooled liquid water in interaction with LiCl

The properties of water above the glass transition temperature are highly controversial. By using time-of-flight secondary ion mass spectrometry (TOF-SIMS), the presence of deeply supercooled water is manifested by dissolution of LiCl in the pure amorphous water films heated at 140-155 K and the formation of aqueous LiCl solutions. Two phases of deeply supercooled water, that lead to the dilute and concentrated LiCl solutions, are clearly identified. The former is short-lived and merges into the latter, whereas the latter is basically identical to normal liquid water as far as the solubility of LiCl is concerned.