The synthesis of a biheterocyclic compound containing two pyrazolone sub‐units, precursor of a new macrocyclic family, is described. It is shown that it is necessary to protect first the pyrazol‐5‐one oxygen site before condensing it with a bifunctional compound in order to obtain a selective alkylation on the heterocyclic nitrogen atom.

No abstract

N-Alkylation of Pyrazolones with OH-Protection.-Alkylation of pyrazole (I) with (II) affords the biheterocyclic product of intramolecular cyclisation (III) instead of the desired compound (VII). Thus, selective protection of the OH function of (I) under mild basic conditions with (IV) in THF (in MeCN N-protection takes place) is necessary for selective N-alkylation to give (VI). The latter is deprotected under mild conditions. -(HICHOUR, M.; MARY, F.; MARZIN, C.; NAJI, M.; TARRAGO, G.; J. Heterocycl. Chem. 30 (1993) 4, 1097-1100; Equipe Chim. Supramol., Univ. Montpellier II, 34095 Montpellier, Fr.; EN)