Chiral phosphorus ligands for the asymmetric conjugate addition of organocopper reagents

The asymmetric conjugate addition of medium order alkyl cuprate reagents. R₅Cu₃Li₂, to 2-cyclohexen-1-one. 2-cyclopenten-1-one and 2-cyctohepten-1-one, with the help of phosphorus ligand B^*, is described. 3-Alkyl substituted cyclohexanones are obtained in essentially optically pure form. The same chiral ligand, associated with CuI, in catalylic amount (10%), allows the asymmetric conjugate addition of Et₂Zn to 2-cyclohexen-1-one.     

On the estimation of mixing coefficients for a multiphase service system

We consider a multiphase service system with a Poisson input flow. Its intensity depends on the number of customers under service. The stationary distribution for this system can be found in an explicit form. We study the rate of convergence to this stationary distribution as well as the bounds for some mixing coefficients. Coupling arguments and Liapunov's function approach form the basis of considerations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Die irreduziblen Darstellungen der Gruppen SL2(Zp), insbesondere SL2(Z2). II. Teil

Ohne Zusammenfassung Unterstützt durch den Schweizerischen Nationalfonds (820.167.73).     

Etude par spectrometrie Raman des complexes de l'iode dans les alcools et les ethers

Laser Raman spectra of iodine-alcohol and iodine-ether solutions have been studied. It was found a new line at 167 cm^?1 for alcohols and at 170 cm^?1 for ethers which is tentatively attributed to an intermediate Hassel complex.     

Synthesis of new nucleoside analogues comprising a methylenecyclobutane unit

Synthesis of eight nucleoside analogues 3-10 with a methylene cyclobutane unit is described. Wittig or Peterson reactions with protected 2-hydroxycyclobutanones 12 and 13 gave E- and Z-derivatives, respectively. After functional modifications the heterocyclic moieties were introduced via a Mitsunobu reaction either on the lateral chain or on the cycle. When adenine was used in this reaction only the N-9 substitution products were obtained. Removal of the protecting groups provided the target products.     

A novel mesoionic ring system: unusual cyclization of thio- and amino-acid derivatives of 6-azauracil

Novel mesoionic heterocyclic structures 8 have been obtained via the internal cyclization of thio- and amino-acid derivatives of 6-azauracil 7b-d. These compounds undergo ring-opening reactions with amines to yield the respective 6-azauracil amides (9) in good yields under microwave irradiation.     

A flexible synthesis of the phytoprostanes B1 type I and II

Syntheses of the enantiomerically pure phytoprostanes B(1) type I and II are described starting from furfural and n-propylfuran. Key steps include the preparation of the Freimanis (+/-)-hydroxycyclopentenone and Wittig coupling using chiral phosphonium salts.