Convenient synthesis of 1-alkoxy-di- and tetrahydrophosphinine 1-oxides by ring enlargement

The double bond of the P-alkoxy 3,4-dimethyl-2,5-dihydro-1H-phosphole 1-oxides reacts easily with dichlorocarbene to give two diastereomers of an unstable adduct useful in the synthesis of ring expanded products, such as 1,2-dihydrophosphinine oxides or 1,2,3,6-tetrahydrophosphinine oxides. The former can be prepared by thermolysis of the adducts, while the latter are obtained by cyclopropane ring opening effected by silver nitrate in an alcoholic solvent. The preparation of the double-bond isomers of 1-alkoxy-tetrahydrophosphinine oxides containing only one methyl substituent in the ring is also described. The reaction of dihydro-1H-phosphole oxides with dichlorocarbene can be modified to give P-alkoxy 1,4-dihydrophosphinine oxides in an unexpected reaction.     

Application of Metathesis Protocols to the Stereocontrolled Synthesis of some Functionalized β-Amino Esters and Azaheterocycles

In this account our aim was to give an insight into the application of metathesis protocols (ROM, RCM, RCEYM, CM, RRM) for the synthesis of various azaheterocyclic frameworks. Due to the high biological potential and importance in peptide chemistry and drug design of β-amino acids our intention is to give a highlight on the synthetic procedures and transformation of these class of compounds with the above-mentioned metathesis strategies with emphasis on selectivity, stereocontrol, substrate-directing effect or functional group tolerance.     

ChemInform Abstract: Equilibrium Structure and Torsional Barrier of BH3NH3.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Highly Chemoselective One-Step Synthesis of Novel N-Substituted-Pyrrolo[3,4-b]quinoline-1,3-diones via Palladium-Catalyzed Aminocarbonylation/Carbonylative Cyclisation Sequence

Novel N-substituted pyrrolo[3,4-b]quinoline-1,3-diones have been prepared via a highly chemoselective palladium-catalyzed carbonylative imidazation-cyclization reaction in a one-pot synthetic approach. This methodology, which has been applied for the first time to access such original scaffolds through two different protocols involving 3-bromo-2-iodoquinoline, as a typical partner, primary amines, and atmospheric or high carbon monoxide pressure (20 bar), has shown an excellent tolerance for many functional groups. The use of bidentate ligands such as XantPhos and dppp, either under atmospheric or high-pressure conditions, provides a wide range of carbonylated compounds in good to excellent yields (up to 82 %). Furthermore, some new quinoline-2,3-dicarboxamides have been isolated as side products in very low yields and have been fully characterized. The solid state structures of three of the synthesized acridinimides have been unequivocally established by single-crystal XRD analysis.     

Revision of the Absolute Configurations of Chelocardin and Amidochelocardin

Even with the aid of the available methods, the configurational assignment of natural products can be a challenging task that is prone to errors, and it sometimes needs to be corrected after total synthesis or single-crystal X-ray diffraction (XRD) analysis. Herein, the absolute configuration of amidochelocardin is revised using a combination of XRD, NMR spectroscopy, experimental ECD spectra, and time-dependent density-functional theory (TDDFT)-ECD calculations. As amidochelocardin was obtained via biosynthetic engineering of chelocardin, we propose the same absolute configuration for chelocardin based on the similar biosynthetic origins of the two compounds and result of TDDFT-ECD calculations. The evaluation of spectral data of two closely related analogues, 6-desmethyl-chelocardin and its semisynthetic derivative 1 , also supports this conclusion.     

Unexpected condensation reaction of two units of 1,2‐dihydrophosphinine 1‐oxides in the presence of tetracyanoethylene

In the presence of tetracyanoethylene, the reaction of two molecules of dihydrophosphinine oxide 2B followed an unexpected route to afford diphosphatricyclododecatrienes 4 instead of the corresponding Diels–Alder cycloadducts ( 3 ). Structures of the products ( 4 ) have been elucidated by a joint application of spectroscopy and quantum chemical calculations. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:29–35, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10062     

Liquid-liquid phase equilibria in polymer solutions and polymer mixtures

The pressure dependence of liquid-liquid equilibria in weakly interacting binary macromolecular systems (homopolymer solutions and blends) will be discussed. The common origin of the separate high-temperature/low-temperature and high-pressure/low-pressure branches of demixing curves will be demonstrated by extending the study into the region of metastable liquid states including the undercooled, overheated and stretched states (i.e. states at negative pressures). The seemingly different response of the UCST-branch of solutions and blends when pressurized (pressure induced mixing for most polymer solutions, pressure induced demixing for most blends) will be explained in terms of the location of a hypercritical point found either at positive (most solutions) or negative pressure (most blends). Further, it is shown that the pressure dependence of demixing of homopolymer solutions and blends may be described using a ‘master-curve’ which, however, is sometimes partly masked by degradation or by vapour-liquid and/or solid-liquid phase transitions. Experimental results demonstrating the extension of liquid-liquid phase boundary curves into the metastable regions will be presented, and the existence of solubility islands in the vicinity of the hypercritical points discussed.     

ChemInform Abstract: Chemical Vapor Deposition of Gallium Nitride from the GaCl3 + NH3 System. Theoretical Study of the Structure and Thermodynamics of Potential Intermediates Formed in the Gaseous Phase.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.