A convenient CeCl3·7H2O/NaI-promoted synthesis of structurally novel and strained tricyclic β-lactams from hydrazines

A convenient synthetic protocol for structurally novel and strained highly derivatized tricyclic β-lactams has been developed. The synthesis involves CeCl3·7H2O/NaI catalyzed addition–condensation of mercaptoacetic acid and N-aroyl-N′-arylidenehydrazines followed by intramolecular cyclodehydration to afford bicyclic 5H-thiazolo[4,3-b][1,3,4]-oxadiazoles, which on treatment with acid chlorides in the presence of triethylamine furnish highly derivatized tricyclic 3H-azetidino[2,1-b]-thiazolo[3,4-d][1,3,4]-oxadiazol-6-ones in 80–93% yields. The process presents an excellent illustration of Ce(III)-catalyzed C–C, C–N and C–S bond formation in a one-pot procedure.