Effect of Protecting Groups and Solvents in Anomeric O-Alkylation of Mannopyranose1

Abstract

Anomeric O-alkylation of mannopyranoses with various protecting groups was investigated using mannose derivatives and 2,3-O-isopropylidene-l-O-trifluoro-methanesulfonyl-D-glycerol (1) as alkylating agent. Generally, in polar solvents higher α/β ratios were obtained than in nonpolar solvents. Sterically demanding protecting groups at the 6-O-position and polar solvents led to higher yields. Reactivity differences were explained by different complex formation. Based on these results mannopyranosyl-α(1-4) glucopyranosides 26 and 27 were synthesized using mannose derivatives 5 and 6 having a 6-O-(p-methoxyphenyl)diphenylmethyl group and galactosyl trifluoromethane-sulfonate 24 or nonafluorobutanesulfonate (nonaflate) 25, respectively, as alkylating agents.     

Highly Selective Copper‐Catalyzed Hydroboration of Allenes and 1,3‐Dienes

The highly selective copper‐catalyzed hydroboration of allenes has been developed. Allylboranes and alkenylboranes were selectively prepared by the judicious choice of catalytic species (copper hydride and boryl copper). Furthermore, two types of alkenylboranes could be selectively synthesized by the choice of an appropriate ligand. Mechanistic studies confirmed that the protonation of a (Z)‐σ‐allyl copper species, which was isolated and structurally characterized by single‐crystal X‐ray diffraction, was a key step in these reactions. Besides allenes, this method is also applicable to the selective hydroboration of 1,3‐diene derivatives to afford allylboranes and homoallylboranes.     

7,7,8,8‐Tetraaryl‐o‐quinodimethane Stabilized by Dibenzo Annulation: A Helical π‐Electron System That Exhibits Electrochromic and Unique Chiroptical Properties

When two benzene rings are fused to a tetraaryl‐o‐quinodimethane skeleton, sterically hindered helical molecules 1 acquire a high thermodynamic stability. Because the tetraarylbutadiene subunit contains electron‐donating alkoxy groups, 1 undergo reversible two‐electron oxidation to 2 ²⁺, which can be isolated as deeply colored stable salts. Intramolecular transfer of the point chirality (e.g., sec‐butyl) on the aryl groups to helicity induces a diastereomeric preference in dications 2 b ²⁺ and 2 c ²⁺, which represents an efficient method for enhancing circular‐dichroism signals. Thus, those redox pairs can serve as new electrochiroptical response systems. X‐ray analysis of dication 2 ²⁺ revealed π–π stacking interaction of the diarylmethylium moieties, which is also present in solution. The stacking geometry is the key contributor to the chirosolvatochromic response.     

The novel approach to indole alkaloids by using Pd(II)-catalyzed cyclization

The synthesis of indole skeleton by using Pd(II)-catalyzed cyclization of the urethane has been achieved. The urethanes with allylic alcohol were converted into vinyl indolines in good yield. The vinyl indoline was transformed into some intermediates of indole alkaloids.     

Synthesis of chlorophyll-a derivatives possessing (un)substituted 13-exo-methylene moiety and their optical properties

Chlorophyll-a derivatives possessing an un/mono/disubstituted methylene moiety at the 13¹-position were prepared by (un)substituted methylation of the 13-carbonyl group and successive dehydration. Substitution of the 13¹-oxo to the methylene group slightly blue-shifted electronic absorption and emission bands in a solution and decreased chemical stability to give an oxidation product cleaved at the E-ring. Further mono/disubstitution at the methylene terminal increased wavelengths of absorption and emission maxima as well as oxidative tolerance.     

Insulated π-conjugated metallopolymers

Recently, there has been a progressive development of insulated π-conjugated metallopolymers with accumulated features of π-conjugated bridging units, transition metal complexes, and encapsulating moieties, as higher-order functionalized materials. A number of insulated conjugated metallopolymers have been successfully synthesized and their fascinating properties have been reported. In addition to the conventional features derived from π-conjugation and transition metals, their insulated structures can compensate for solubility, a disadvantage in conventional metallopolymers, and enhance their functionalities, such as sensing, luminescence, and conduction. In this review, we summarize the synthetic methodologies, structural characteristics, and functionalities of one-dimensional insulated π-conjugated metallopolymers, while focusing on the effect of transition metals and insulation on their properties.     

Synthesis,Crystal Packing,and Ambipolar Carrier Transport Property of Twisted Dibenzo[g,p]chrysenes

A versatile method for the synthesis of dibenzo[g,p]chrysene (DBC) derivatives based on regio‐ and stereoselective stannyllithiation to diarylacetylenes is described. This method affords a variety of DBCs possessing both electron‐donating and electron‐withdrawing functional groups. These twisted molecules take brickwork packing structures in single crystals. Thus, ambipolar carrier transport properties with mobility values of up to 10^?3 cm² V^?1 s^?1 in the amorphous state were achieved. Functional groups on DBC frameworks are considered to increase carrier mobility through the enhancement of intermolecular interactions in the brickwork packing structures.     

Magnetic resonance force microscopy combined with surface topography

A new method of surface microscopy is proposed, which combines three-dimensional electron spin resonance imaging by magnetic resonance force microscopy (MRFM) and topographic imaging of the sample surface by scanning force microscopy (SFM). In order to demonstrate its potential for the identification of microscale objects, the individual and combined images are used to provide the locations, shapes and spin density distributions of target phantom objects. We report spatial resolution in MRFM of 2.8 x 2.8 x 2.0 microm(3). This could be improved to the theoretical limit of 0.08 x 0.08 x 0.04 microm(3) through reduction of the thermal noise by cooling to cryogenic temperatures approximately 0.5K. We believe that this type of microscopy will become a very useful tool for the investigation of anomalies induced in surfaces by materials buried below the surface.     

Single-mode single-polarization holey fiber using anisotropic fundamental space-filling mode

We present the single-mode single-polarization regime of a circular-hole holey fiber consisting of a core with large elliptical holes. The elliptical holes in the core, which produce large anisotropies, split the fundamental mode into two orthogonally polarized fundamental modes, often referred to as slow and fast modes. This fiber can guide only one polarization state of the fundamental mode when a fundamental space-filling mode index of the cladding region is designed to lie between these indices of the slow and fast modes of the core region. We demonstrate one design example of this fiber and show that the single-polarization regime can be achieved over a wide wavelength range.