Macrocyclization of alpha-(alkynyloxy)silyl-alpha-diazoacetates by inter-/intramolecular

Thermally induced intra-/intermolecular [3 + 2] cycloaddition reaction sequences of alpha-(alkynyloxy)silyl-alpha-diazoacetates 1 lead to [3.3](1,4)pyrazolophanes (2)2 and higher cyclooligomers thereof [(2)n, n > 2]. In most cases, the cyclodimer was isolated by crystallization, while a complete separation of the mixture of the higher cyclooligomers was not possible. Solid state structures of cyclodimers (2b)2 and (2c)2, cyclotrimer (2b)3, and cyclotetramer (2e)4 were determined by X-ray diffraction analysis. Field-desorption mass spectra were used to characterize the cyclooligomer mixtures. The relative amounts of the cyclooligomers depend on the substitution pattern of the diazo compound. The cyclooligomerization reactions reported herein demonstrate, for the first time, the involvement of diazo functions in macrocyclization reactions via 1,3-dipolar cycloaddition.     

Adaptive FEM–BEM coupling with a Schur complement error indicator

In this paper an a-posteriori error estimate for non-linear coupled FEM–BEM equations is derived by using the Steklov–Poincaré operator and hierarchical basis techniques. We obtain “local” error indicators which are based on two-level subspace decompositions with the additive Schwarz operator. We present an algorithm for adaptive error control which is driven by these error indicators and numerical results are included.     

Kristall- und molekülstruktur von hexaphenyldistannylselenid (C6H5)3SnSeSn(C6H5)3

The crystal and molecular structure of hexaphenylditin selenide (C₆H₅)₃SnSeSn(G₆H₅)₃ was determined by X-ray diffraction data and was refined to R  0.055. The compound is monoclinic, space group P2₁, with a  9.950(4), b  18.650(7), c  18.066(6) Å, β  106.81(4)°, Z  4. The two molecules in the asymmetric unit differ slightly in their conformations, both having approximate C₂ symmetry. Bond lengths and angles are: SnSe 2.526 (2.521(3) ? 2.538(3)) Å; SnC 2.138 (2.107(16)?2.168(19)) Å; SnSeSn 103.4(1)°, 105.2(1)°. There are only slight angular distortions at the SnSeC₃ tetrahedra (SeSnC angles: 104.3(5)?114.8(4)°). The bond data indicate essentially single bonds around the Sn atoms.     

THE SYNTHESIS OF THIENO[2,3 C]ISOTHIAZOLE AND DERIVATIVES

Abstract

The major product formed by the action of phosphorus pentasulphide on 2 ethoxallyl 4,4 diethoxybutyronitrile has been shown to be 3 ethoxycarbonylthieno[2,3 c]isothiazole (1, R[dbnd]COOC₂H₅).     

ChemInform Abstract: Novel Alkaline Earth Metal Chalcogenoborates: Syntheses and Crystal Structures of Sr4.2Ba2.8(BS3)4S and Ba7(BSe3)4Se.

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