Solid-phase synthesis and stereochemical assignments of tenuecyclamides A-D employing heterocyclic amino acids derived from commercially available Fmoc alpha-amino acids

[reaction: see text] The solid-phase assembly of heterocyclic amino acids enabled the total synthesis of numerous diastereoisomers of tenuecyclamides A-D, establishing or correcting the stereochemistry of each natural product. This strategy provides a very efficient route to synthesize thiazole- and oxazole-containing macrolactams from heterocyclic amino acids that are readily prepared from Fmoc-alpha-amino acids. This methodology appears to be broadly applicable to the synthesis of natural product libraries incorporating unnatural heterocyclic amino acid residues for the purpose of drug discovery.     

The preference for anti over Gauche migration in the Baeyer-Villiger reaction

Explanations for stereoselectivity in the Baeyer-Villiger reaction have relied on the assumption that the antiperiplanar (app) group migrates. However, the magnitude of the preference for app-migration over gauche migration is unknown. To investigate this, the energy differences between the two were estimated from ab initio calculations. App-migration was found to be the preferred pathway since no transition structure could be located for gauche migration. Barriers for gauche migration were estimated by performing constrained optimizations. App-migration was found to be strongly favored with a barrier that is at least 3.8 kcal/mol and as much as 58.0 kcal/mol lower in energy than the gauche migration barrier.     

Rhodium catalysed tandem conjugate addition-protonation: an enantioselective synthesis of 2-substituted succinic esters

The rhodium catalysed addition of potassium trifluoro(organo)borates to dimethyl itaconate generates an intermediate complex which on protonation provides enantioenriched succinic esters.     

Honeycombs, herringbones and brick-walls; three-fold guest-dependent variation in copper trimesate complexes bearing sulfimide ligands

Reaction of a solution of CuSO(4) and S,S'-diphenylsulfimide, Ph(2)SNH 1, with sodium salts of trimesic acid (H(3)tma) in MeOH gives the 2-D coordination network [Cu(3)(Ph(2)SNH)(6)(tma)(2)] in which each trimesate is bound to three copper centres. Addition of other solvents to the reaction mixture causes a change in the shape of the network. By this route, three forms have been prepared and characterised by X-ray crystallography. These include the known honeycomb, 2, and brick-wall, 3, motifs and a herringbone, 4, arrangement which is novel for transition metal-containing trimesate complexes. Key to the supramolecular isomerism observed is the ability of 1 to facilitate structural isomerism at copper(II) centres. In contrast to 2 in which the copper centres are square planar, 4 is analogous to an inter-allogon, with both planar and tetrahedral copper centres. Also prepared is a related complex which is composed of discrete units of three copper centres. These are further linked into a 2-D network by hydrogen bonds.     

INVESTIGATION OF THE ATRP OF n-BUTYL METHACRYLATE USING THE Cu(I)/N,N,N'''',N",N"-PENTAMETHYLDIETHYLENETRIAMINE CATALYST SYSTEM

INTRODUCTIONThe atom transfer radical polymerization (ATRP) has become an important method for preparing well-definedmacromolecules. This technique offers control over the molecular weights, the chain end functionalities, and thechain architectures[1-12]. It has been used extensively for the preparation of homopolymers, block, and randomcopolymers[13-39], for the preparation of organic/inorganic hybrid materials[40-54], as well as for combining variousother living polymerization methods …     

The investigation of an equilibrium dependent reaction for the formation of enamines in a microchemical system

The paper describes the equilibrium dependant reaction for the formation of enamines in a microchemical system utilising electroosmotic flow (EOF) for fluid mobilisation. The authors have shown that the reaction can be carried out without the presence of a Lewis acid catalyst, in addition the enamine intermediate was synthesised at room temperature using mild solvent conditions. A 42% conversion of cyclohexanone into the enamine has been achieved to date.     

Parameter-free quasiparticle calculations for YH3

Electronic structure calculations for YH3 within the local density approximation result in a metallic ground state with the bands at the Fermi energy overlapping by more than 1 eV, whereas a band gap of 2.8 eV is deduced from optical experiments. Here, we report the results of parameter-free GW calculations which predict a fundamental gap of 1 eV. When we take into account electric dipole matrix elements a large optical gap of almost 3 eV is obtained. A combination of photoemission and inverse photoemission spectroscopy could test the prediction of a small fundamental band gap.