Etudes sur les composés organométalliques,XIII [1] Action d'organomagnésiens sur la benzalacétone

The reactions of benzalacetone with n-BuMgBr and PhMgBr have been compared with the corresponding reactions with the diorganomagnesium complexes of ether and pyridine. The results obtained by using different mole ratios of reactants and orders of addition show that the conjugated addition reaction is enhanced if a monomeric diorganomagnesium reagent is available; this condition can be realized either by adding a diorganomagnesium complex to the ketone or by complexing the diorganomagnesium with pyridine. Probable reaction mechanisms for normal and conjugated addition reactions are suggested.     

Etudes sur les composés organométalliques V [1]. Action de la pyridine sur les organomagnésiens

By the action of pyridine on various Grignard reagents at room temperature, new diorganomagnesium complexes R₂Mg · 2pyridine (R=Ph, n-Bu, t-Bu and Et) were prepared and analyzed. Anomalous results were obtained with methyl- or benzylmagnesium reagents.     

Addition de dérivés maloniques sur des β-énaminones cycliques

The addition of activated acctonitriles 6 on cyclic and benzylic β-enaminoketones 5 under basic conditions (sodium ethoxide or trition B) have been investigated. This reaction leads exclusively to the formation of α-pyrones 8 and never to the pyridine ring. The strucutre of the newly synthesized α-pyrone derivatives 8 are supported by nmr and ir spectral data.     

Etude sur les composés organométalliques III [1]. Action d'organomagnésiens sur des complexes du tétrachlorure de titane

The reaction between RM_gX and TiCl₄,2L (L = pyridine, piperidine or quinoleine) is shown to give a high yield of organo-titanium (IV) compounds. As expected, the decomposition of the latter is reduced to a minimum by the ligand L initially present, allowing the preparation of etheral solutions of R₄Ti (R = benzyl, phenyl or butyl). R₄Ti is obtained whatever may be the initial molar ratio of RM_gX/TiCl₄, 2L.     

L'ernploi du tétrafluoroborate de triéthyloxonium et ses limites,dans l'éthylation d'oxo-2 indolinc earboxanilides et thioearboxanilides

The reaction of triethyloxonium tetrafluoroborate (Meerwein's reagent) with 2-oxo indoline 3-carboxanilides ( 4 ) gives mainly the 2-ethoxyindole derivatives, together with other C- and O-ethyl compounds. In the same time, difluoro indolyloxyboranes are formed by the reaction of the anilides 4 with boron trifluoride resulting from the decomposition, in situ, of the Meerwein's reagent. These results clearly indicate some limitation for synthetic applications of this reagent.     

Expedient Approach to 6‐Bromo‐2‐isopropylidenecoumaranone,a Potential Intermediate for the Synthesis of TMC‐120B,Pseudodeflectusin, and Their Congeners

A straightforward approach toward 6‐bromo‐2‐isopropylidenecoumaranone, a potential intermediate toward alkaloid TMC 120‐B, pseudodeflectusin, and other natural products, was reported. The synthetic sequence involved the reaction of 3‐bromosalicylaldehyde with chloroacetone and cyclization of the resulting ether to a 2‐acetylcoumaranol intermediate. This was followed by sequential methyl Grignard addition and Jones’ oxidation to the corresponding coumaranone, which was dehydrated to the final product with the methanesulfonyl chloride/pyridine reagent. The protection of the coumaranol as the corresponding THP‐ether resulted in improved product yields.     

Etude en serie as-triazine. X. Réactions nucleophiles sur les triazines-1,2,4 ones-5

The action of Grignard reagents on 6-methylas-triazin-5-one and some methyl derivatives has been studied. The orientation of the reaction is controlled mainly by steric hindrance between the reagent and the substituent at position 6. Comparative studies using lithium aluminum hydride have also been carried out.     

Influence d'une fonction ester ou acide portée par la chaîne alcoxyle sur la réactivité des sels de N-alcoxypyridinium envers les ions cyanures

Study of the reactivity towards cyanide ions, of N-alkoxy-pyridinium salts bearing an ester group in the α-position of their alkoxy chain, shows that a decomposition to pyridine and α-carbonyl ester competes with cyanopyridine formation. This competitive decomposition can become predominant as the acidity of the α-hydrogen is increased. In spite of its steric crowding, which brings an increase in the 4-cyanopyridine ratio, the salt 3 , which presents a tertiary α-carbon, reacts normally. Salts carrying an -α or -β acid group show a very reduced reactivity due to an unfavourable pH diminution and to the formation of a betaine which is less reactive than alkoxy-pyridinium ion. A folded conformation of this betaine would explain a relatively enhanced reactivity of the 4-position as compared to the reactivity of the 2-position of the pyridine ring.     

Etudes sur les composés organométalliques. XI [1]. Action du tétrabutoxytitane sur des solutions de Grignard

The reaction of titanium tetra-n-butoxide with phenylmagnesium bromide inether has been investigated. The species (C₆H₅)₂Mg in the Grignard reagent leads to (C₆H₅)₄Ti, whereas the dimeric species (C₆H₅)₂Mg · MgBr₂ produces an insoluble complex mTi(OBu)₄ · n[(C₆H₅)₂Mg · MgBr₂]. Applied to other Grignard reagents, the use of R₂Mg allowed the preparation of tetrabenzyltitanium, tetracyclohexyltitanium and tetramethyltitanium. Cristalline (C₆H₅)₄Ti and (C₆H₅CH₂)₄ Ti have been isolated.     

Transition-metal chloride mediated addition reaction of diorganomagnesium to easily enolizable ketones

An alkylation to an easily enolizable ketone, such as β-tetralone, is difficult to perform with Grignard reagent (RMgX) or with diorganomagnesium (R₂Mg), because a deprotonation to form a magnesium enolate occurs predominantly. To avoid the prior enolization, a complex reagent of a transition-metal salt and R₂Mg was examined: A combination of R₂Mg with iron(II) chloride (FeCl₂) or ytterbium(III) chloride (YbCl₃) gave a complex reagent that can realize a nucleophilic reaction to β-tetralone prior to the enolization. A combination of RMgX with these metal salts is inferior to a combination of R₂Mg with them to obtain the nucleophilic complex reagent.     

Iron‐Catalyzed C?H Bond Activation for the ortho‐Arylation of Aryl Pyridines and Imines with Grignard Reagents

Direct arylation of the ortho‐C? H bond of an aryl pyridine or an aryl imine with an aryl Grignard reagent has been achieved by using an iron‐diamine catalyst and a dichloroalkane as an oxidant in a short reaction time (e.g., 5 min) under mild conditions (0 °C). The use of an aromatic co‐solvent, such as chlorobenzene and benzene, and slow addition of the Grignard reagent are essential for the high efficiency of the reaction. The present arylation reaction has distinct merits over the previously developed reaction that used an arylzinc reagent, such as its reaction rate and atom economy. Selective C? H bond activation occurs in the presence of a leaving group, such as a tosyloxy, chloro, and bromo group. Studies on a stoichiometric reaction and kinetic isotope effects shed light on the reaction intermediate and the C? H bond‐activation step.     

Réactivité de l'hypochlorite de tertiobutyle dans l'oxydation du benzothiophene

In reaction with benzothiophene, t-butyl hypochlorite acts as an oxidizing reagent and a chlorination reagent. A mixture of 3-ehlorobenzothiophene, three 2,3-dichloro-2,3-dihydrobenzothio-phene 1-oxide isomers (trans-anti: trans-syn; cis-anti) and 2-chlorobenzothiophene 1-oxide was obtained. With a large exces of t-butyl hypochlorite, the reaction leads to 2,3-dichlorobenzothio-phene, 2,3-dichlorobenzothiophene 1-oxide. 2,2,3-trichloro-2,3-(lihydrobenzothiophene 1-oxide and 2,3-dichloro-3-oxobenzothio-phene 1-oxide. In any case, oxidation stops at the level of the sulfoxide.     

Stéréochimie en pentacoordination. Apport des réactifs inducteurs de déplacement chimique à l'etude de spirophosphoranes à liaison P?H

The NMR spectra of eight spirophosphoranes bearing a P? H bond have been recorded in the presence of europium NMR shift reagent. The spectra are simplified by addition of the europium chelate. The observed displacements in the proton NMR lines allow the assignment of the endo and exo signals in some cases. By addition of the NMR shift reagent, one observes a displacement in the phosphite-spirophosphorane equilibrium in some cases.     

Synthesis of 2-carbamoylmethyl-6-β-D-ribofuranosylpyridine with the aid of a Pd(0)-catalyzed reaction

D-Allo/D-altro-2-(2,4:3,5-di-O-benzylidenepentitol-l-yl)-6-ethoxycarbonylmethylpyridine was synthesized from 2-bromo-6-(2,4:3,5-di-O-benzylidenepentitol-1-yl)pyridine or 2-(2,4:3,5-di-O-benzylidenepentitol-1-yl)-6-iodopyridine by means of a tetrakis(triphenylphosphine)palladium(O)-catalyzed reaction with Reformatsky's reagent. Subsequent ammonolysis and mesylation of the D-altro-ethoxycarbonylmethyl compound gave D-altro-2-carbamoylmethyl-6-(1-O-mesyl-2,4:3,5-di-O-benzylidenepentitol-l-yl)pyridine which was cyclized to 2-carbamoylmethyl-6-β-D-ribofuranosylpyridine.     

Régiospécificité de la cycloaddition des diarylnitrilimines sur quelques dérivés indoliques

In this paper, we describe the results of a study of the reaction of diaryl nitrilimines with N-ethylindole ( 1 ) and 2-methoxycarbonyl-N-ethylindole ( 2 ). The regioselectiivity of the reaction is reversed when going from 1 to 2 as it has been spectroscopically and chemically demonstrated.     

Synthesis of dimethyl heterocyclic‐o‐dicarboxylates using dimethyl acetylenedicarboxylate

Dimethyl acetylenedicarboxylate (DMAD) is a very important and useful reagent for the preparation of dimethyl heterocyclic‐o‐dicarboxylates, which are key intermediates in the synthesis of fused pyridazine derivatives. The synthesis of thiopyranes by the Diels‐Alder reaction of dithiocarboxylate derivatives, synthesis of various cyclazines by [2 + 8] cycloaddition reactions, and synthesis of dimethyl pyrazolo[3,4‐b]pyridine‐5,6‐dicarboxylates and polycyclic heterocycles containing the 1,6‐naphthyridine ring system by the reaction of o‐aminonitrile compounds with DMAD are described here.     

Efficient synthesis of cellulose furoates in 1-<Emphasis Type="Italic">N</Emphasis>-butyl-3-methylimidazolium chloride

The ionic liquid 1-N-butyl-3-methylimidazolium chloride ([C₄mim]⁺Cl⁻) was investigated as reaction media for the homogeneous acylation of cellulose with 2-furoyl chloride in the presence of pyridine. The preparation of cellulose furoate depending on the reaction conditions, the cellulose type and the pyridine content was studied. Cellulose furoates with a degree of substitution in the range from 0.46 to 3.0 were accessible, i.e., under mild conditions, with a low excess of reagent and in a short reaction time. The products were characterized by elemental analysis, perpropionylation, ¹H- and ¹³C NMR spectroscopy and FTIR spectroscopy. Thomas Heinze is the member of the European Polysaccharide Network of Excellence (EPNOE), www.epnoe.eu     

Réactions de Friedel et Crafts de dérivés aromatiques sur les composés dioxo-1,4,2,3-non saturés. IV. Réactions des hydroxy-5-ouchloro-5-diméthyl-3,5- ou diméthyl-4,5-dihydro-2,5-furannones-2

Friedel-Crafts reactions of aromatic derivatives with 1,4-dicarbonyls 2,3-éthylenic compounds. Part IV. Reactions of 5-hydroxy or 5-chloro 3,5-dimethyl or 4,5-dimethyl 2 (5 H) furanones We studied the Friedel-Crafts reactions of 2-(5H)-furanones. In the presence of sulfuric acid and of an aromatic derivative, 5-hydroxy- or 5-chloro-5-methyl-2-(5H)-furanones with one methyl group either in the 3 position, or in the 4 position generally give the corresponding 5-aryl-2-(5H)-furanones, while with aluminium chloride, it is possible to obtain, when a reaction takes place, isomeric 1H-indenecarboxylic acids. However, in a particular case, an addition to the substrate's double bond is observed. The 3-aryl-5-hydroxy-tetrahydrofuran-2-one obtained is methylated in two ways and gives either a cyclic product, or a linear one. In two cases tautomerism between 1H-1-indenecarboxylic acid and 1H-3-indenecarboxylic has been shown by ¹H-NMR.     

Etude des reactions de substitution homolytique sur le noyau pyridinique; influence de l'acidite du milieu

Homolytic substitution by the l-n-undecyl radical at positions 2 and 4 of the pyridine nucleus results from thermal decomposition of dodecanoyl peroxide in acetic acid. Rate dependence on pH shows that pyridine protonation increases the rate of addition of the alkyl radical to the pyridine ring but decreases the rate of the reaction of the intermediate radical with the peroxide. Results are interpreted in terms of orbital interaction theory.     

Action de l'acide fluorhydrique sur les azirines : synthèse d'α-fluorocétones et de difluoroamines - étude de l'orientation de la réaction

Addition of Olah's reagent in benzene or methylene chloride to azirines leads to the formation of difluoroamines or α-fluoroketones. This reaction has been applied to the synthesis of 17 α-fluoropregnenolone. The formation of fluoroketone proceeds via a cationic intermediate. Yield is improved when using a more nucleophilic fluorinating reagent obtained by addition of triethylamine to Olah's reagent.