Complementary to enantioselective transformations of planar functionalities, catalytic desymmetrization of meso compounds is another fundamentally important strategy for asymmetric synthesis. However, experimentally established stereochemical models on how a chiral catalyst discriminates between two enantiotopic functional groups in the desymmetrization of a meso substrate are particularly lack...

5(4H)-Oxazolones can be formed through the activation of acylated α-amino acids or of peptide C termini. They constitute potentially activated intermediates in the abiotic chemistry of peptides that preceded the origin of life or early stages of biology and are capable of yielding mixed carboxylic-phosphoric anhydrides upon reaction with phosphate esters and nucleotides. Here, we present the re...

Aminoacyl adenylates (aa-AMPs) constitute essential intermediates of protein biosynthesis. Their polymerization in aqueous solution has often been claimed as a potential route to abiotic peptides in spite of a highly efficient CO2-promoted pathway of hydrolysis. Here we investigate the efficiency and relevance of this frequently overlooked pathway from model amino acid phosphate mixed anhydride...

An efficient and odourless procedure for a one-pot synthesis of thioesters by the reaction of benzoic anhydrides, thiourea and various organic halides (primary, allylic, and benzylic) or structurally diverse, electron-deficient alkenes (ketones, esters, and nitriles) in the presence of Et3N has been developed. In this method, thiobenzoic acids were in situ generated from the reaction of thioure...

The unique properties of epoxy polymers have led to their wide application in various fields modern technology. influence the structure bisphenols on polymers, especially thermal ones, is known. However, chemical hardener also affects cured polymers. As hardeners, we used acid hardeners structures: anhydrides maleic, phthalic, pyromellite, methyltetrahydrophthalic and other acids. following giv...

New unsymmetrical trans-stilbenes have been prepared by the sequential coupling reactions of bromobenzenesulfonate with formylarylboronic acids, benzylphosphonates and arylmagnesium bromides and characterized. The nickel-catalyzed reactions of stilbenesulfonates with aryl Grignard reagents produced the corresponding stilbenes via the nucleophilic aromatic substitution of the neopentyloxysulfony...

metal complexes, ml (m=ni, cu, co and zn) of unsymmetrical tetradentate schiff base have been synthesized by the template reaction of the half-units n-(1-hydroxy-2-acetonaphthone)-1-amino-2-phenyleneimine)(hl1) with 2-pyrroleca-rbaldehyde. the complexes have been characterized by elemental analysis, ir, 1h nmr and uv spectroscopy. the crystal structure of the ni(ii) complex has been determine...

This thesis presents methods for air sampling and determination of isocyanates, amines, aminoisocyanates and anhydrides. These organic compounds are generated during production or thermal degradation of polymers such as polyurethane (PUR) or epoxy. Isocyanates, amines and anhydrides are airway irritants known to cause occupational asthma. Some of the isocyanates and diamines are listed as human...

The energy performance and radial force of a mixed flow pump with symmetrical and unsymmetrical tip clearance are investigated in this paper. As the tip clearance increases, the pump head and efficiency both decrease. The center of the radial force on the principal axis is located at the coordinate origin when the tip clearance is symmetrical, and moves to the third quadrant when the tip cleara...

A novel way of synthesizing unsymmetrical disulfides from thiols with DDQ is presented here. This procedure ran in a straightforward manner to give high product yields. Unsymmetrical disulfides were directly synthesized from the corresponding mixture of thiols in equimolar amounts under mild conditions. 2011 Elsevier Ltd. All rights reserved.