Structures de deux β-énaminoesters cycliques: l'α-(tétrahydropyrrolidinylidéne-2) acétate d'éthyle et l'α-(hexahydroazepinylidéne-2) acétate d'éthyle

The structure of ethyl α-(tetrahydro-2-pyrrolidinylidene) and α-(hexahydro-2-azepinylidene) acetates has been determined from the X-ray crystallographic analysis. The results show that, in a solid state, these compounds exist as β-enaminoesters which have a Z configuration. They also show the presence of intra and intermolecular hydrogen bonding.     

Un nouvel exemple de transposition: l'épimérisation en C(3) d'hydroxy-3-δ1-pyrazolines dérivées de sucres

A Novel Example of Reversible Ring Opening: The Epimerization at C(3) of Sugar 3-Hydroxy-Δ¹-pyrazolines Reaction of 1 (either geometrical isomer) with hydrazine followed by in situ Ag₂O oxidation led to two pairs of interconverting isomers 4 ? 5 and 6 ? 7 . By the same treatment, (Z)- 10 and (or) (E)- 10 gave the pair 11 ? 12 . Acetylation of 4 ? 5 led to a non interconverting mixture of 8 and 9 . This fact, and the lack of incorporation of ¹⁸O when the epimerization took place in the presence of H₂¹⁸O indicated that the most probable mechanism consisted in a reversible ring opening ( D ? E ? F ). The kinetic parameters of these reactions are given and structural assignments proposed for the new compounds.