Chiral allyl cations are captured by furan with 100% stereoselectivity: synthesis of enantiopure 2-alkoxy-8-oxabicyclo

A low-temperature (-95 degrees C) protocol for intermolecular cycloadditions of furan to chiral silyloxyallyl cations in dichloromethane is described. Key precursors are open-chain, mixed a-ketoacetals, which are chiral. The resulting [4+3] cycloadducts are densely functionalized and are isolated as single enantiomers in high chemical yield. The yield of the cycloadducts increases with increasing dilution. Three and four stereogenic centres are created in one single step.     

The behaviour of some α,α′-dibromoketones on electron impact. An analogy to the reductive removal of bromine in solution

The relative importance of the rearrangement ions [M ? Br ? CO]⁺, [M ? Br₂ ? CO]⁺ and [M ? HBr₂ ? CO]⁺ in the mass spectra of the title compounds is compared with the amounts of α-methoxyketone formed on reduction of these compounds with a Zn/Cu couple in methanol. It is suggested that the quantitative correlation found reflects the electron releasing powers of the substituents on the α carbons.     

Application of Laser-ICP-MS in environmental analysis

Laser sampling inductively coupled plasma mass spectrometry has been used for the quantitative determination of trace elements in samples of environmental significance. Solid sampling in environmental analysis is a very demanding type of application: in fact, the instrumental conditions must be carefully chosen and optimized to minimize signal fluctuations, the vaporized material introduced into the plasma should be representative to the composition of the whole sample and a suitable calibration method must be developed. The analytical problems addressed are: determination of elements in plant ash and their direct determination in growth rings of oaks.     

Synthesis of 6S, 7S-anhydro-serricornine.

Diastereoselective and enantioselective reduction of the β-ketoester $\text{3}$ by yeast to $\text{4}$ provided the chiral starting material for a synthesis of 4RS,6S,7S-serricornine, having the same configuration as the natural product. This material was converted into optically active and diastereomerically pure 6S,7S-anhydro-serricornine ($\text{2}$).     

Bis(diphenylphosphano)alkan- und 1-(Diphenylphosphano)-2-(2-pyridino)ethan-N-Arylsulfinylamin-Nickel(0)-Komplexe

Bis(diphenylphosphano)alkane- and 1-Diphenylphosphano-2-(2-pyridino)ethane-N-arylsulfinylamine Nickel(0) Complexes Synthesis and properties of the bis(diphenylphosphano)alkane-N-phenyl-sulfinylamine-nickel(0) complexes [Ni{Ph₂P(CH₂)_nPPh₂}(PhNSO)] (n = 2 dppe, n = 3 dppp, n = 4 dppb) as well as of the 1-(diphenylphosphano)-2-(2-pyridino)ethane nickel(0) complexes [Ni(dpppe)₂], [Ni(dpppe)(p-TolNSO)] and [Ni(dpppe)(PPh₃)₂] are described. These compounds have been characterized by i. r. and ³¹P n.m.r. spectroscopy. The N-arylsulfinylamine ligands are η²-(N, S)-side on coordinated.     

Synchrotron radiation circular dichroism spectroscopy of ribose and deoxyribose sugars, adenosine, AMP and dAMP nucleotides.

Synchrotron radiation circular dichroism (SRCD) spectra of ribose and deoxyribose sugars, adenosine, AMP and dAMP nucleotides and cyclic derivatives were measured in the vacuum ultraviolet region (down to 168 nm for sugars and 175 nm for adenine derivatives) and at different pH values (3, 6-7, 9-10) and temperatures (between 5 and 45 degrees C). The information content in the VUV region is important since the CD bands strongly depend on the chemical structure of the sugar, the presence and orientation of a phosphate group and the protonation state of adenine. On the other hand, single or double deprotonation of the phosphoric acid group has no influence on the spectra. We assign the vacuum ultraviolet (VUV) CD bands of the nucleoside and nucleotides to be due mainly to n-->pi* transitions in the adenine nucleobase based on a comparison with the absorption spectra. The CD bands of the sugars are due to n(O -->sigma*) transitions and are much smaller than the CD signal from the nucleotides in the VUV region. Bands are assigned to both pyranose and open-chain forms.