Facile, efficient, and enantiospecific syntheses of 1,1'-N-linked pseudodisaccharides as a new class of glycosidase inhibitors

This article describes an efficient synthesis of a potent trehalase inhibitor, 1,1'-N-linked pseudodisaccharide 1 (consisting of two valienamines), in 14 steps with an overall yield of 12% and a first synthesis of 2 (consisting of two 2-epi-valienamines) in 15 steps with an overall yield of 24% from (-)-quinic acid. The synthesis involves a stereospecific palladium-catalyzed coupling reaction between an allylic amine and an allylic chloride as the crucial step. The acetonide blocking groups were shown to be the best hydroxyl protecting groups, compatible with the palladium-catalyzed allylic amination reaction that afforded high yields of the 1,1'-N-linked pseudodisaccharides with a minimum amount of an elimination diene side product.     

Aryl Diazonium Salt‐Triggered Cyclization and Cycloaddition Reactions: Past,Present, and Future

Aryl diazonium salts occupy a privileged role in synthetic chemistry owing to their ready availability and versatile reactivity. While their applications in accessing diversely functionalized arene derivatives via denitrogenation‐coupling and reduction/addition reactions have been well recognized by practitioners in both academia and industry, recent renaissance in chemical transformations of retaining the key N₂‐unit has emerged as a powerful technique to construct various N‐heterocycles. This review covers the history and latest advances in cyclization and cycloaddition reactions using aryl diazonium salts as N₂‐annulation synthons. The scope, applications, and opportunities in exploring new chemical space by this sustainable strategy are summarized and discussed.     

Synthesis, emission, and electrochemical properties of luminescent dinuclear zinc(II) chalcogenolate complexes. Dynamic 1H NMR studies and X-ray crystal structure of [(bpy)Zn2(SC6H4-Cl-p)(mu-SC6H4-Cl-p)(mu-OAc)2

A series of novel luminescent dinuclear zinc(II) diimine complexes with bridging chalcogenolate ligands have been synthesized, in which the two zinc atoms were found to exist in different coordination environment. The luminescence and electrochemical behavior of these complexes have been studied. These complexes have also been shown to exhibit dynamic fluxional behavior in solution due to an exchange of the bridging and terminal thiolate ligands. The mechanism and kinetics of which have been investigated by variable-temperature 1H NMR studies. The X-ray crystal structure of [(bpy)Zn2(SC6H4-Cl-p)(mu-SC6H4-Cl-p)(mu-OAc)2] has also been determined.     

Resonance raman spectra and excitation profiles of soret-excited metalloporphyrins

Resonance Raman spectra of nickel, chromium, and copper porphyrins, excited at their Soret maxima, show decreasing scattering intensity due to depolarized modes. This order correlates with diminished ¹Q(0-0) absorption in the porphyrins. The data are interpreted in terms of Jahn-Teller distortions in both Q and B states. General agreement between predicted and observed excitation profiles of nickel etioporphyrin I support a vibronic treatment of the excited states. The effect of tight focusing of the incident beam is to quench most Raman scattering intensity, except the 1384 cm^?1 line of the nickel complex.     

A de novo enantioselective total synthesis of (-)-laulimalide

An enantioselective total synthesis of the naturally occurring anticancer agent (-)-laulimalide is described. The synthesis is characterized by extensive use of new reaction methodologies based on catalytic asymmetric acyl halide-aldehyde cyclocondensation (AAC) reactions and transformations of the derived enantioenriched beta-lactones. The synthesis also incorporates a unique allenylstannane glycal acetate alkylation and chemoselective ring-closing metathesis reaction.     

Monte Carlo simulations of liquid crystals near rough walls

The effect of surface roughness on the structure of liquid crystalline fluids near solid substrates is studied by Monte Carlo simulations. The liquid crystal is modeled as a fluid of soft ellipsoidal molecules and the substrate is modeled as a hard wall that excludes the centers of mass of the fluid molecules. Surface roughness is introduced by embedding a number of molecules with random positions and orientations within the wall. It is found that the density and order near the wall are reduced as the wall becomes rougher, i.e., the number of embedded molecules is increased). Anchoring coefficients are determined from fluctuations in the reciprocal space order tensor. It is found that the anchoring strength decreases with increasing surface roughness.     

Structural Aspects of the β‐Polymorph of (E)‐4‐Formylcinnamic Acid: Structure Determination Directly from Powder Diffraction Data and Elucidation of Structural Disorder from Solid‐State NMR

Among the derivatives of (E)‐cinnamic acid for which the solid‐state photochemical properties have been studied, (E)‐4‐formylcinnamic acid ( 1 ) has already received much attention. Given the inability to prepare single crystals of the β‐polymorph of 1 that are of suitable size and quality for structural characterization by single‐crystal X‐ray diffraction, the structure of this material was determined directly from powder X‐ray‐diffraction data by means of the genetic‐algorithm technique for structure solution, followed by Rietveld refinement. High‐resolution solid‐state ¹³CNMR was also applied to elucidate details of structural disorder concerning the orientation of the formyl group, and provided independent support for the disorder model established form the Rietveld refinement. The reported structure establishes that the β‐phase of 1 is not structurally anomalous among photoreactive (E)‐cinnamic acid crystals, and finally resolves a long‐standing controversy concerning the structural properties of this material.     

Photoluminescent metal-sulfur clusters derived from tetrathiometalates: metal-to-metal charge-transfer excited states of d0-d10 heterobimetallic sulfido clusters with bulky phosphine ligands

Reactions of MS4(2-) (M = Mo, W) with M'(PCy3)X (M'=Ag/Au, X= ClO4/Cl) and [Cu2(dcpm)2(MeCN)2](ClO4)2 (dcpm = bis(dicyclohexylphosphino)methane) afforded heterometallic sulfido clusters [M'2(PCy3)2(MS4)] (M=Mo, M'=Au: 2; M=W, M'=Ag: 3, Au: 4) and [Cu4(dcpm)4(MS4)](ClO4)2 (M=Mo: 5 x (ClO4)2, W: 6 x (ClO4)2), all of which, except 4, have been characterized by X-ray structure determination. Clusters 5 x(ClO4)2 and 6 x (ClO4)2 feature unusual 16-membered [Cu4P5C4] metallamacrocycles formed on the respective tetrathiometalate anion templates and have unusually long Cu-S bonds and Cu...M distances for metal sulfur clusters that contain a saddle-shaped [Cu4MS4] core. Low-energy absorption bands are observed in their electronic spectra at approximately 562 and 467 nm, respectively, assignable to MMCT transitions; quasireversible reduction waves are observed with E(1/2) = -1.43 (52+) and -1.78 V (62+) versus FeCp2(0/+); and they are emissive either in the solid state or in solution. The emission of 6(2+) can be quenched by both electron acceptors, such as methylviologen, or electron donors, such as aromatic amines, with the excited state reduction potential E(62+*/6+) estimated to be approximately 1.13V versus a normal hydrogen electrode.