René Csuk

Magnesium- and Titanium-induced Reductive Coupling of Carbonyl Compounds: Efficient Syntheses of Pinacols and Alkenes

Finely dispersed magnesium on graphite was found to be a totally selective single-electron transfer reagent of general utility for the reduction of various kinds of carbonyl and dicarbonyl compounds to pinacols, a reaction quite compatible with a number of functional groups. Similarly, titanium on graphite proved to be a universally applicable reducing agent for the efficient conversion of pinacols, carbonyl and dicarbonyl compounds into alkenes and cycloalkenes respectively and for the cyclization of oxo alkanoates to enol ethers, facilitating and unifying the highly useful McMurry reaction. The practicability of the presently known carbonyl coupling methods is discussed in the light of these results.

N.M.R. Spectroscopy of Fluorinated Monosaccharides

Publisher Summary This chapter discusses the application of nuclear magnetic resonance (NMR) spectroscopy for the analysis of fluorinated monosaccharides. Within the past two decades, the importance of NMR spectroscopy has enlarged tremendously. Its advantages over other methods in the structural and conformational analysis of complex molecules such as natural products, and particularly with regard to the still-increasing importance of medical investigations using NMR techniques, is abundantly evident. Because destruction of the sample is avoided, different NMR experiments can be performed repeatedly and the analysis of the spectra is usually convenient, simple, and fast. This methodology is exceptionally free from artifacts, thus, allowing the detailed analysis of conformational behavior in solution in comparison with the conformation in the solid state. Double- and triple-resonance techniques and isotopic labeling of compounds, together with the use of Fourier-transform spectroscopy at very high field-strength now allows the acquisition of high-resolution, NMR spectra. Because of these great improvements, all magnetic nuclei can now be used in the NMR analysis of fluorinated monosaccharides including 1H, 13C, 15N, and 19F.

Graphite-Metal Compounds

Publisher Summary This chapter discusses the most recent and important developments in the field of graphite and the structural properties and use of these compounds in organic and organometallic chemistry. Graphite has a lamellar structure, with an interlayer distance of 0.335 nm. Besides the large number of reagents that can be intercalated, a number of different types of graphites are used. The most commonly used potassium–graphite intercalation compound, C 8 K, shows an interlayer distance of 5.34 A, and all carbon layers are separated by a layer of K. Differences among the alkali metals in behavior toward graphite have been explained in terms of electron transfer. Pure yellow, first-stage compounds of Ba and Sr with graphite were prepared by the direct action of metal vapor on graphite in metallic tubes sealed under vacuum. C 8 K in toluene, benzene, or isopropylbenzene can act as an alkylation catalyst in the presence of ethylene to yield the corresponding nuclear and side chain-alkylated aromatic hydrocarbons. Graphite intercalation compounds can act as mild anionic polymerization initiators offering some benefits in comparison to analogous reactions in homogeneous medium or to metal dispersions.

A facile synthesis of 1,2,-o-isopropylidene-β-L-idofuranurono-6,3-lactone

Abstract A simple, high yield, two step synthesis of 1,2,-O-isopropylidene-β-L-idofuranurono-6,3-lactone is described.

A new, zinc-promoted synthesis of 1,4(1,5)-anhydro-2-deoxy-pent-(hex)-1-enitols (furanoid and pyranoid glycals)

Activated zinc in tetrahydrofuran efficiently converts derivatives of furanosyl and pyranosyl halides into glyacals.

Efficient, Low Temperature Reformatsky Reactions of Extended Scope

Laminated zinc/silver–graphite reacts rapidly at low temperatures with α-bromo- and α-chloro-alkanoates and cyclic ketones allowing high yielding and even stereospecific Reformatsky reactions.

SYNTHESIS OF CARBOHYDRATE DERIVED α-METHYLENE-γ-LACTONES BY DIASTEREOSELECTIVE, LOW TEMPERATURE REFORMATSKY-TYPE REACTIONS

Abstract Hexopyranoside- and hexofuranose uloses with either ethyl 2-(branamethyl)acrylate in the presence of laminar Zn/Ag-graphite or ethyl 2-(trimethylsilylinethyl)acrylate/tetra-n-butylanrnonium fluoride undergo stereoselective branching, mainly with formation of spiro α-methylene-γ-lactones.

Biocatalytical transformations II. Enantioselective hydrolysis of N-acetyl-fluoro-phenylalanine-ethylesters by lyophilised yeast☆

Abstract The three nuclear substituted monofluoro D-N-acetylphenylalanine-ethylesters were obtained in excellent yield via enantioselective hydrolysis of their respective racemates by use of lyophilised yeast ( Saccharomyces cerevisiae Hansen).

BRANCHING OF KETOSUGARS BY EHTYL TRIMETHYLSILYL-ACETATE/TETRA-n-BUTYLAMMONIUM FLUORIDE

Abstract Hexopyranose- and hexofuranose-uloses, on treatment with ethyl trirnethylsilylacetate/tetra-n-butylammohium fluoride, form β-hydroxy esters or derivatives thereof instead of their TMS-enol ethers. 29Si NMR studies confirm the proposed mechanism.

Synthese von enantiomerenreinem (2R)-1-Oxo-2-methyl-oxazin@@@Synthesis of enantiomeric pure (2R)-1-oxo-2-methyl-oxazine (short communication): Kurze Mitteilung

A synthesis of enantiomeric pure (2R)-1-oxo-2-methyl-oxazine (3), starting fromL-2-Chloropropionic isobutylester and ethanolamine is reported.