A new route to 6-azachromones. An improved synthesis of 2-azaxanthone

Condensation of the morpholine enamine of 1-benzyl-4-piperidone with β-ketoesters yielded 6-azatetrahy-drochromones which were debenzylated and aromatized to 6-azachromones; 2-azaxanthone has been thus obtained with an improved yield as compared to previous syntheses.     

General analysis ofn-loop corrections in the 2PPI variational approach to λφ4

We present the general analysis of then-loop contribution in a new variational approach to quantum field theory, applied to the scalar model λφ⁴, which is based on the use of an effective action for the local composite operator \(\hat \phi ^2 \) . In a previous paper [1] the three-loop analysis was performed and it was found that the differences with the one loop calculation were very small. We have now generalised this argument for any arbitrary but finite loop calculation. In particular, we examine stability of the precarious phase.     

Alkylation of natural endoperoxide G3-factor. Synthesis and antimalarial activity studies

Alkylation of the peroxyhemiketal function is described and all synthesised endoperoxides show good antimalarial activity. New rearrangement reactions in the presence of CsCO3, and preliminary results on Fe(II) chemical reduction of the O-O bond are presented.     

An efficient asymmetric oxidation of sulfides to sulfoxides

The Sharpless reagent (Ti(OiPr)₄ + 1 mol eq. diethyl tartrate (DET) + 2 t-BuOOH) modified by addition of one mol eq. H₂O gives a new homogeneous reagent which cleanly oxidizes sulfides into sulfoxides in dichloromethane. The best results were obtained for the stoichiometry Ti/DET/H₂O/t-BuOOH = 1:2:1:2. The e.e. observed ranged from 4 to 93% with the highest beeing observed in the case of methyl p-toly] sulfoxide.     

Tétraazamacrocycles lipophiles: Extraction d'ions métalliques par une résine imprégnée

Lipophilic Tetraazamacrocyles: Extraction of Metal Ions by Impregnated Resin Extraction of Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and Ag⁺ by lipophilic tetraazamacrocycles dispersed on a solid matrix (Amberlite XAD7) is reported. Extraction efficiency is sensitive to the metal ion identity and the cavity size of the macrocycle. The influence of kinetic factors upon extraction efficiency is discussed.     

Réactions de cyclisation de pentynyl-2 pyrimidones-4

Acetylenic amindines HC≈?C·(CH₂)_n·C(?NH)NH₂ give, by condensation with β-ketoesters, pyrimidones substituted on carbon 2 by an acetylenic chain. Two types of evolution are observed when compounds are heated without any catalyst. The minor route is a cyclization by attack on a triple bond by the amidic nitrogen atom. The main reaction is a cycloaddition involving the non activated triple bond and an azadienic system, leading to non isolated tricyclic intermediates which retrocyclize to stable bicyclic compounds.     

Crystal structure and hydrogen bonding system in cellulose I(alpha) from synchrotron X-ray and neutron fiber diffraction

The crystal and molecular structure, together with the hydrogen-bonding system in cellulose I(alpha), has been determined using atomic-resolution synchrotron and neutron diffraction data recorded from oriented fibrous samples prepared by aligning cellulose microcrystals from the cell wall of the freshwater alga Glaucocystis nostochinearum. The X-ray data were used to determine the C and O atom positions. The resulting structure is a one-chain triclinic unit cell with all glucosyl linkages and hydroxymethyl groups (tg) identical. However, adjacent sugar rings alternate in conformation giving the chain a cellobiosyl repeat. The chains organize in sheets packed in a "parallel-up" fashion. The positions of hydrogen atoms involved in hydrogen-bonding were determined from a Fourier-difference analysis using neutron diffraction data collected from hydrogenated and deuterated samples. The differences between the structure and hydrogen-bonding reported here for cellulose I(alpha) and previously for cellulose I(beta) provide potential explanations for the solid-state conversion of I(alpha) --> I(beta) and for the occurrence of two crystal phases in naturally occurring cellulose.     

Isomérisation cis-trans en Série Alkyl-4-vinyl-3-pipéridine par Sigmatropie [3.3]. Synthèse des Epivinyl Isomères des Alcaloïdes du Quinquina

cis, trans Isomerization of 4-Alkyl-3-vinylpiperidines by [3.3] Sigmatropic Rearrangement. Synthesis of Epivinyl Isomers of Cinchona Alkaloids Isomerization of 4-alkyl-3-vinylpiperidines induced by formaldehyde has been studied for ethyl meroquinate and quinotoxine. The equilibration of cis- and trans-isomers occurs by involvement of a [3.3] sigmatropic rearrangement. This process permits an easy access to the trans-isomers from natural products of cis-configuration and has been used to obtain the epivinyl isomers of cinchona alkaloids.     

Synthesis and reactivity of pyrrolo[1,2-α]quinoxalines. Crystal structure and AM1 calculation

2-Methylquinoxaline reacts with ethyl bromopyruvate giving 2-substituted pyrrolo[1,2-α]quinoxalines. The yield of the condensation depends on the functionalization of starting materials, and optimization is obtained with 2-dimethylamino-3-methylquinoxaline ( 1c ). Reactivity of the resulting pyrrolo[1,2-a]-quinoxalines was investigated and supported by a theoretical approach (AM1 calculation performed with the MOPAC 6.0 software). X-ray analysis of 5 which crystallizes in the monoclinic system, space group P2₁/n, with a = 9.095(1), b = 8.972(1), c = 17.749(3) A, β = 96.56(1)°, is also reported.