Direct carbamoylation of alkenyl halides

Alkenyl chlorides and bromides are converted into tertiary enamides by treatment with a carbamoylsilane in toluene at 110 degrees C in the presence of phosphine-palladium(0) catalysts. [reaction: see text]     

Half-monopoles in the Yang-Mills theory

Using a gauge-invariant characterization of monopoles defined via their centres, we investigate the generic topological field pattern for the three-dimensional Yang-Mills theory. This leads to field patterns with one-half winding number. After presenting the main features through the simpler case of half-vortices, we consider half-monopoles in detail.     

Silver-gelatin method for determination of inorganic peroxides in alkaline solution

An aqueous solution of gelatin binds silver(I) at pH >7 and a yellow silver sol can be produced from this by reduction. The sol reacts with peroxide in strongly ammoniacal medium to give a colourless solution. The reaction may be used for photometric and visual titration of peroxide with relative standard deviations of 0.4 and 1.5% respectively and also for its spectrophotometric determination.     

Synthetic studies on the molybdenum cofactor: Total synthesis of pterindithiolenes by direct dithiolene formation from suitable pterin alkynes

A novel, efficient total synthesis of a series of pterindithiolenes (15, 16, 17 and 18) [(5,6-dihydro-[1,4]dithiin or 6,7-dihydro-5H-[1,4]dithiepin systems respectively for six and seven membered dithiolenes] has been reported. The six membered quinoxaline thioketal 9 and seven membered quinoxaline dithiolene 11 have also been synthesized from quinoxaline acetylenic alcohol 5 and the corresponding acetylenic ketone 10 respectively. The synthesis of five membered pterin thioketals 12 and 13 along with the conversion of 13 to the dithiolene 14 by the reaction with NBS is also reported.     

Iminium ion-enamine cascade reaction enables the asymmetric total syntheses of aspidosperma alkaloids vincadifformine and ervinceine

Asymmetric total synthesis of (+)-vincadifformine and (+)-ervinceine is reported by utilizing an iminium ion triggered cascade reaction using chiral 3,3-disubstituted piperidine imine and 2,3-disubstituted indole derivatives coupling partner. In the first generation total synthesis, the pivotal imine is prepared in excellent stereoselectivity but in moderate yield involving a Birch reduction-alkylation strategy. Furthermore, to improve upon the synthesis of the decisive imine, the more practical second generation route is devised through a Johnson-Claisen rearrangement to access chiral 3,3-disubstituted piperidinone in excellent yield and stereoselectivity. Apart from synthesizing (+)-vincadifformine, this strategy is also exploited for the first asymmetric total synthesis of (+)-ervinceine employing an iminium ion mediated cascade reaction. This distinctive strategy simultaneously sets up two new rings, two new stereogenic centers, and three new sigma bonds in a single operation.     

Multicomponent one pot synthesis of C-glucosides of 1-azaindolizines

Abstract

A protocol based on Groebke-Blackburn-Bienayame (GBB) multicomponent reaction has been developed for efficient and atom economical synthesis of C-glucosides of 1-azaindolizine, i.e. 2-(β-D-glucopyranosyl)-3-N-alkylamino-1-azaindolizine. Thus, a series of fourteen novel 2-(β-D-glucopyranosyl)-3-N-alkylamino-1-azaindolizines have been synthesized in moderate to good yields by reaction of a perbenzylated β-C-glucopyranosyl aldehyde with differently substituted 2-aminopyridines and alkyl isocyanides using InCl₃ as acid catalyst. All synthesized β-C-glucosides were unambiguously characterized with the help of spectroscopic (IR, ¹H-NMR, ¹³C-NMR and mass spectra) data analysis.     

An amyloid-like fibril-forming supramolecular cross-β-structure of a model peptide: a crystallographic insight

The peptide Boc-Val-Phe-OMe 1 bearing sequence similarity with the central hydrophobic cluster (CHC) of Alzheimer's Aβ(18-19) peptide self-assembles to produce amyloid-like straight unbranched fibrils as examined by atomic force microscopy and Congo red assay. Single crystal X-ray diffraction offers the atomic level structure of the supramolecular parallel β-sheet aggregation and antiparallel separation between layers (cross-β-structure).