N‐Alkylation of pyrazolones with OH‐protection

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.