Synthesis of diaminomethylidene derivatives of tetronic acid

Methyl 4-chloro-3-oxobutanoate reacts with benzoylcyanamide in the presence of catalytic amounts of Ni(acac)₂ to give the corresponding ketene N-benzoylaminal, which is transformed in boiling AcOH into 3-(amino)(benzoylamino)methylidene]tetrahydrofuran-2,4-dione. Debenzoylation of the latter in the presence of EtONa in EtOH yields a N,N-unsubstituted diaminomethylidene derivative of tetronic acid. Cyclization of the adduct of methyl 4-chloro-3-oxobutanoate with benzoylcyanamide in the presence of triethylamine follows a different pathway leading to methyl 2-amino-1-benzoyl-4-oxo-4,5-dihydro-1H-pyrrole-3-carboxylate.