Nouvelle voie d'acces a des allenes et vinylallemes enantiomeriquement enrichis.

The reduction of three racemic propargylic bromides by Hiyama's reagent (CrCI₂ in THF) in the presence of protonic chiral reagents and HMPT efficiently affords optically active allenic compounds with an enantiomeric purity of 15–25%.     

Nouvelle voie d'acces aux dihydro-3,4-2H-benzoxazines-1,3

3,4-Dihydro-2H-1,3-benzoxazines were prepared from primary amines and dihalocompounds by a method which can lead to compounds dissymetrically substituted in positions 2 and 4.     

Nouvelle voie d'acces au diethylacetal de l'amino-2 cyano-3 formyl-5 pyrazine

An unequivocal two step synthesis of 2-amino-3-cyano-5-formylpyrazine diethylacetal, starting from dimethylaminoacrolein and O-tosylisonitrosomalononitrile, is described. This pyrazine is a key intermediate for the preparation of folic acid and various analogues.     

Effet de longueur d'onde et controle par la geometrie de l'etat fondamental de la photoisomerisation de derives de l'hexatriene-1,3,5

Irradiations at different wavelengths (313, 254, 229 and 214 nm) of the 4 geometric isomers of 5-phenyl-1,3,5-heptatriene show that the photochemical behaviour of these trienes is mainly controlled by their ground state equilibrium.     

Sur une voie d'acces commode aux aldehydes,cetones et amides α-alleniques.

α-allenic aldehydes, ketones or amides are easily prepared from 1,1-bisubstituted α-allenic alcohols by nickel peroxide oxidation.     

Influence de la longueur d'onde sur la photoisomerisation de derives de l'hexatriene-1,3,5

Kinetic studies of photoisomerization of 1-phenyl 6-methyl-cyclohexa-1,3-diene, and of the four isomeric 5-phenylhepta-1,3,5-trienes, have been performed at 313, 254, 228 and 214 nm. Photoreactions of these compounds are dependent on the wavelength of irradiation. Photolysis at short wavelength of Z,E-5-phenylhepta-1, 3,5-triene initiates a new reaction, sigmatropic [1,5] hydrogen migration, forming an ene-allenic compound. Thermal reactivity data for polyenic compounds supports the assigned structures.     

Contribution a l'etude de la transformation thermique des aldazines α-ethyleniques. nouvelle voie d'acces aux pyrazoles halogenes ou substitues par des groupements phenoxy,thiophenoxy et thioethoxy en 3(5)

Azines of β-halogen-, aryloxy-, alkylthio- and arylthio-substituted acroleines when heated gave pyrazole derivatives which may be hydrolysed very easily to give N-unsubstituted pyrazoles bearing in the 3(5) position halogen, ArO, RS or ArS groups. The observed heterocyclisation was compared with thermal decomposition of cinnamald azine for which an ionic mechanism had been previously proposed, whereas we show that the involved mechanism is an internal 1,4-addition and, according to the nature of the migrating group, a thermal [1,3] or [1,5] sigmatropic rearrangement.     

Nouvelle voie d'accès aux isochromènes

Reaction of monophosphonium salt derived from α,α-dibromo-o-xylene with sodium carboxylates, followed by action of base, gives isochromenes.