ChemInform Abstract: 4-Iminocyclobutenones: Synthesis and Building-Blocks of Aminohydroquinones and Annulated Quinolines.

Two methods are presented for the synthesis of the title compounds starting from cyclobutenediones: an alkoxide substitution approach and a Staudinger reaction. Unsaturated lithiumorganyls may be added to the remaining carbonyl group and on heating lead to ring enlargement in a cascading process. 4-Alkenyl or 4-aryl derivatives yield aminophenols or -naphthols; 4-alkynyl compounds give cyclopenta-annulated quinolines. © Georg Thieme Verlag Stuttgart

4-iminocyclobutenones: Synthesis and building-blocks of aminohydroquinones and annulated quinolines

Two methods are presented for the synthesis of the title compounds starting from cyclobutenediones: an alkoxide substitution approach and a Staudinger reaction. Unsaturated lithiumorganyls may be added to the remaining carbonyl group and on heating lead to ring enlargement in a cascading process. 4-Alkenyl or 4-aryl derivatives yield aminophenols or -naphthols; 4-alkynyl compounds give cyclopenta-annulated quinolines. © Georg Thieme Verlag Stuttgart

Highly regioselective monothionation of squaric and semisquaric acid derivatives

An efficient synthesis of 4-thioxocyclobut-2-enones by the action of 0.5 molar equivalents of Lawesson's reagent on the corresponding diones is reported

Highly regioselective monothionation of squaric and semisquaric acid derivatives

An efficient synthesis of 4-thioxocyclobut-2-enones by the action of 0.5 molar equivalents of Lawesson's reagent on the corresponding diones is reported

The Disordered High-Temperature Structure of (NH4)3H(SO4)2\mathrm{(NH_4)_3H(SO_4)_2} and Its Relationship to the Room-Temperature Phase

The structure of letovicite, (NH4)(3)H(SO4)(2) has been redetermined at 293 and 420K. At room temperature the structure crystallizes monoclinic, space group C12/c1 (no. 15), with lattice parameters a = 15.418(5) Angstrom, b = 5.905(5) Angstrom, c = 10.223(5) Angstrom and beta = 102.806(5)degrees. The structure is composed of two symmetrically independent isolated NH4+ tetrahedra and [SO4-H-SO4](3-) dimers with a symmetrical hydrogen bond connecting the two sulfate tetrahedra. At 420 K the structure is rhombohedral, space group R (3) over barm (no. 166) with lattice parameters a = 5.9039(5) and c = 22.5360(6) Angstrom. While the low-temperature phase is completely ordered, this does not hold for the high-temperature phase: the hydrogen and oxygen atoms which constitute the hydrogen bond are disordered with the consequence that the hydrogen bond is now strongly asymmetric. Furthermore, the hydrogen atoms in one of the two symmetrically independent NH4+ tetrahedra are disordered and have probably some share in the high protonic conductivity which has so far been attributed mainly to the hydrogen atom of the hydrogen bond. (C) 2002 Elsevier Science (USA)

Natural titanite and malayite: structural investigations and the 500K anomaly

Titanite, CaTiSiOS, and malayaite, CaSnSiOs, are isostructural. Both minerals exhibit a thermal anomaly near 500 K but diffuse reflections only occur in titanite. Titanite crystals from Rauris, Austria (Fe 1.8%, A1 3.8%) were studied using synchrotron X-ray diffraction, IR spectroscopy and high-resolution transmission electron microscopy (HRTEM). The phase transformation near 500 K is smeared out by impurities. The diffuse scattering disappears above 830 K. No antiphase boundaries were found in natural titanite. High-temperature X-ray diffraction and IR spectroscopy were used to study the thermal anomaly in malayaite. Structure determinations of malayaite at different temperatures reveal a discontinuity in the evolution of the anisotropic Debye-Waller factors of the Ca atoms near 500K. At this point IR spectra show a break in the temperature dependence of the intensity of the 533cm−1mode and the peak positions of the 499cm−1mode and the Si-0 stretching mode near 908cm−1