Albert Robert

Synthèses d'esters ou d'acides α-halogènes à partir des gem dicyano époxydes

Resume Les gem dicyano epoxydes reagissent facilement avec les hydracides en milieu alcoolique, ou aqueux, pour conduire de facon selective et en une operation aux esters ou aux acides α-halogenes.

Reaction des dicyanoepoxydes avec les reactifs binucleophiles azotes ou avec leurs halohydrates. Nouvelles syntheses en serie imidazole et imidazole condense

Abstract Contrary to the reaction of gem dicyano epoxides with thiocarbonyl binucleophilic reagents, nitrogen binucleophilic reagents react in a first step with one nitrile group of the epoxides. The reaction leads to enaminoimidazoles. The two carbons of the epoxides act as potential electrophilic centers when these epoxides are reacted with halohydrates of nitrogen binucleophilic reagents. The reaction is a one pot selective synthesis of imidazoles and condensed imidazoles.

Electrosynthesis and redox behavior of vinylogous TTF displaying strong conformational changes associated with electron transfers

Abstract The redox properties of a series of substituted vinylogous tertrathiafulvalenes (TTF) prepared by oxidative coupling of 1,4-dithiafulvenes (DTF) have been investigated in acetonitrile and dichloromethane. The different steps of the electrodimerization mechanism have been characterized: fast electron transfer, coupling between two cation-radicals and slow deprotonation. Through the substituent choice of DTF, it is possible to control the relative stabilities of the different redox species of the electrogenerated vinylogous TTF. According to the nature and position of the substituent, the structural changes induced by the steric interactions lead to a compression of potential (where the second electron is easier to remove than the first one), or on the contrary to a large increase of the separation between the first and second oxidation potentials (by comparison with similar molecules without steric hindrance). Density functional modeling calculations and detailed analysis of the electrochemical behavior have been used to rationalize the substituent effect. A good agreement with the occurrence of an EE mechanism in which the electron transfer is concerted with the conformation changes is found. The inner reorganization energies are low (0.35–0.45 eV) allowing a fast passage between the different conformations during the electron transfers.

Unsymmetrical and highly-conjugated tetrathiafulvalene and selenatrithiafulvalene derivatives: synthesis and reactions of novel heterocyclic Wittig–Horner reagents

Novel 1,3-dithiole and 1-selena-3-thiole Wittig–Homer reagents have been developed and used in the efficient synthesis of a range of new, unsymmetrical tetrathiafulvalene and selenatrithiafulvalene derivatives (6)–(10) and (16); cyclic voltammetry establishes that these molecules are efficient π-donors.

Short and efficient synthesis of new α-oximino esters

Abstract α-Cyano α-alkoxy carbonyl epoxides 1 react, in refluxing alcohol, with hydroxylamine hydrochloride 2 in a direct ring opening reaction to give β-alkoxy α-oximino esters 4 in good yields. We have shown that this reaction proceeds through the formation of chlorohydrons 3.

A simple synthesis of New Push-Pull substituted imidazoles by chemoselective nucleophilic attack of α-cyano epoxides

Abstract A chemoselective reaction of amidines or guanidines with α-cyano epoxides leads to new 4-amino-5-carbethoxy or 4-hydroxy-5-cyano or 4-carbethoxy-5-aryl- imidazoles depending on the steric hindrance of the epoxides and on the reaction medium.

Dication charge transfer salts of TTF vinylogues

TTF vinylogues were electrochemically synthesized and dication charge transfer salts were isolated. Important conformational changes between the neutral and oxidized states were observed by X-ray structure analysis.

Reaction of dicyano epoxides with thiocyanate ion: route to α-thiocyanato derivatives or to 2-acetylimino-1,3-oxathioles and X-ray crystal structure of 2-acetylimino-4-(4-tolyl)-1, 3-oxathiole-5-carbonitrile

β-Aryl dicyano epoxides reacted as synthetic equivalents of ketene dications with KSCN in aq. dimethyl sulfoxide or EtOH, or with NH4SCN in acetonitrile, to give α-thiocyanato derivatives. When Ac2O was used as a solvent, the 1,3-oxathiolane intermediates were trapped as 2-acylimino-1,3-oxathioles. This new synthetic route to 1,3-oxathioles was extended to 1,3-oxaselenoles by using KSeCN as the reactant in Ac2O. The crystal structure of an important intermediate compound, 2-acetylimino-4-(4-tolyl)-1,3-oxathiole-5-carbonitrile, was determined by means of X-ray diffraction.

Cycloaddition reactions of the anhydro-4-hydroxythiazolium hydroxide system with dimethyl maleate and dimethyl fumarate: X-ray determination of the exo structure of the cycloadducts

Abstract The relative configuration of the carbons bearing the ester groups in the cycloadducts of anhydro - 4- hydroxythiazolium hydroxides with dimethyl maleate and dimethylfumarate is revised in the light of an X-ray crystallographic analysis. Steric effects are considered to account for the preferred exo approach of the dipole and the dipoiarophile.

Cathodic synthesis of powerful electron π-donors including dithiadiazafulvalenes

Intramolecular coupling of bis(2-ethylthio-1,3-thiazolium) salts upon electrochemical reduction leads to dithiadiazafulvalenes (DTDAF). These novel π-electron donor molecules show extremely high donating properties compared to their sulfur analogues, tetrathiafulvalenes (TTF). In addition we report that a DTDAF precursor substituted by a dithiafulvenyl group undergoes dimerization upon oxidation to afford vinylogous TTF. Cathodic coupling of the corresponding tetra(2-ethylthio-1,3-thiazolium) salt leads to a new donor including two different donor families: DTDAF and vinylogous TTF.