Synthèse et propriétés des aroylhydrazones du benzoate d'éthyle. Synthèses d'hétéroscycles azotes

The aroylhydrazones of ethyl benzoate have been prepared in fair yield by the action of aroylhydrazines on ethyl benzimidate hydrochloride. These products give rise, quantitatively, at their melting point, to 5-aryl-2-phenyl-1,3,4-oxadiazoles, and, in the presence of hydrazine hydrate, in boiling 1-propanol to 4-amino-5-aryl-3-phenyl(4H)-1,2,4-triazoles (Yields 50%). The addition of methylmagnesium iodide to these products give aroylhydrazones of acetophenone.     

Structure des peroxydates obtenus par action de lóxygene moleculaire sur des organometalliques derives du bromure de crotyle

Butenylmagnesium, butenylzinc and butenylaluminium bromides are oxidized at low temperature (?80 and ?100°C). The qualitative and quantitative studies of the reaction products after reduction by PPh₃, LiAlH₄ and n-BuMgBr show that the secondary structure is dominant in the peroxides formed.     

Ultrafast back electron transfer processes in the photoexcited methylviologen-iodide charge transfer complexes

The ultrafast back electron transfer in the excited charge transfer complexes of the methylviologen with iodide ions has been investigated using femtosecond transient absorption spectroscopy. Methylviologen and iodide form two types of charge transfer complexes each characterized by a charge transfer band in the same spectral region. At low I^- concentrations mainly a 1:1 complex MV²⁺(I^-) is present while at high I^- concentrations both 1:1 and 1:2 complexes MV²⁺(I^-)₂ can be observed. Ultrashort laser pulses at 400 nm are used to excite both complexes in their charge transfer band. The observed transient absorption can be represented by a biexponential function with 1 ps and 20 ps time constants and attributed to the decay of the MV^+./I^. and MV^+./I₂ ^.- radical pair respectively. The excitation of the 1:1 complex leads to the formation of the MV^+./I^. radical pair while the excitation of the 1:2 complex leads to the formation of the MV^+./I^. and MV^+./I₂ ^.- radical pairs.     

Synthesis of 4‐(2‐hydroxyphenyl)‐1‐phenyl‐1,2,4‐triazolidine‐3,5‐dione derivatives through cyclic transformations of 3‐(2‐phenylcarbazoyl)‐2(3H)‐benzoxazolone derivatives

Four 3‐(3‐benzylidene‐2‐phenylcarbazoyl)‐2(3H)‐benzoxazolone derivatives 3 have been synthesized from benzoxazolone derivatives 1 and benzaldehyde N‐chloroformylphenylhydrazone 2. By acid hydrolysis, these compounds yielded 3‐(2‐phenylcarbazoyl)‐2(3H)benzoxazolone derivatives 4 which were not isolated and were transformed via an intramolecular reaction into 4‐(2‐hydroxyphenyl)‐1‐phenyl‐1,2,4‐triazolidine‐3,5‐dione derivatives 5 in a good yield. Attempts to cyclize these compounds by intramolecular elimination of water into tricyclic compounds 6 with various dehydrating agents were unsuccessful.     

What can be learned from femtochemistry: the H bond in water

A non-empirical theory is presented showing how infrared pump–probe spectroscopy can be used to measure subpicosecond variations of the oxygen–oxygen distribution functions in liquid water, Δg(r, τ). It should be emphasised that the equations derived in the present contribution are exact up to the second order in the perturbation expansion. These equations are model independent and provide a route to predict time-dependent radial distribution functions that are measured by time-resolved X-ray when the out-of-equilibrium configuration is produced by an optical pump pulse. It is shown that the profiles of OH stretching bands of HDO/D₂O can be brought into a full coincidence with Δg(r, τ). We thus prove that femtosecond pump–probe experiments are indeed useful to measure the time dependency of a H bond length. The theoretical framework developed in the present contribution is applicable to any H bonded system and especially to the field of bio-molecules or bio-system where H bonds play a key role in the unfolding/folding mechanism.     

New Synthesis of l-Ribofuranose Derivatives from l-Arabinose

Abstract

There is a need for l-ribofuranose derivatives suitable for the preparation of l-nucleosides which could be employed to build nucleases resistant ‘antisense’ oligonucleotides¹ and to prepare analogues as potential inhibitors of HIV.² Such l-ribofuranoside derivatives were previously obtained by epimerisation at C-2 of l-arabinose in the presence of molybdenic acid³ and by inversion of configuration at C-2 of l-arabinose and C-3 of l-xylose by nucleophilic displacement of a sulfonate group.⁴ In both cases, the desired l-ribofuranoside derivative has to be separated from some remaining starting material. Another method to obtain l-ribose involved the complete inversion of d-ribono-1,4-lactone followed by reduction.⁵ We report herein a new transformation of l-arabinose into l-ribofuranose derivatives.     

Fragmentation sous l'Impact Electronique d'Amino-4 triazole-1,2,4 ones-5

The mass spectra of several 4-amino-1,2,4-triazole-5-ones with different groups in position 1 have been recorded and show new skeletal rearrangements and hydrogen migrations. The comparison of the ‘normal’ and mass analysed ion kinetic energy spectra obtained by the ‘simili MIKE’ technique permits the determination of the molecular ion and fragment ion structures and also the mechanism of formation of these ions. These results show that the molecular ion of the N-1 unsubstituted 4-amino-1,2,4-triazole-5-ones exists in the gas phase in two tautomeric forms.