Recent Advances in Transition Metal-Catalyzed Glycosylation

Having access to mild and operationally simple techniques for attaining carbohydrate targets will be necessary to facilitate advancement in biological, medicinal, and pharmacological research. Even with the abundance of elegant reports for generating glycosidic linkages, stereoselective construction of α- and β-oligosaccharides and glycoconjugates is by no means trivial. In an era where expanded awareness of the impact we are having on the environment drives the state-of-the-art, synthetic chemists are tasked with developing cleaner and more efficient reactions for achieving their transformations. This movement imparts the value that prevention of waste is always superior to its treatment or cleanup. This review will highlight recent advancement in this regard by examining strategies that employ transition metal catalysis in the synthesis of oligosaccharides and glycoconjugates. These methods are mild and effective for constructing glycosidic bonds with reduced levels of waste through utilization of sub-stoichiometric amounts of transition metals to promote the glycosylation.     

Synthesis of a new sulfonated monomer for poly(aryl ether)s

A new sulfonated monomer suitable for polyarylether synthesis was made. 1,1'‐(p‐Phenylenedioxy)bis[4‐(4‐fluorobenzoyl)]benzene was prepared from phosphorus pentoxide/methanesulfonic acid (PPMA), 1,4‐diphenoxybenzene, and p‐fluorobenzoic acid in good yield. This compound was selectively monosulfonated on the most activated ring with fuming sulfuric acid and isolated as the sodium salt. Poly(aryl ethers) made from this monomer may find use as proton exchange membranes. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:553–556, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20137     

R(4, 5) = 25

The Ramsey number R(4, 5) is defined to be the least positive integer n such that every n-vertex graph contains either a clique of order 4 or an independent set of order 5. With the help of a long computation using novel techniques, we prove that R(4, 5) = 25. © 1995 John Wiley & Sons, Inc.     

Hamiltonian cycles in cubic 3-connected bipartite planar graphs

We show that 3-connected cubic bipartite planar graphs with fewer than 66 vertices are Hamiltonian.     

Hierarchical models and chaotic spin glasses

Renormalization-group studies in position space have led to the discovery of hierarchical models which are exactly solvable, exhibiting nonclassical critical behavior at finite temperature. Position-space renormalization-group approximations that had been widely and successfully used are in fact alternatively applicable as exact solutions of hierarchical models, this realizability guaranteeing important physical requirements. For example, a hierarchized version of the Sierpiriski gasket is presented, corresponding to a renormalization-group approximation which has quantitatively yielded the multicritical phase diagrams of submonolayers on graphite. Hierarchical models are now being studied directly as a testing ground for new concepts. For example, with the introduction of frustration, chaotic renormalization-group trajectories were obtained for the first time. Thus, strong and weak correlations are randomly intermingled at successive length scales, and a new microscopic picture and mechanism for a spin glass emerges. An upper critical dimension occurs via a boundary crisis mechanism in cluster-hierarchical variants developed to have well-behaved susceptibilities.