Reactivity of curcumin and curcuminoid β-diketones with o-aminothiophenol: synthesis of 1,5-benzothiazepines

Four new 1,5-benzothiazepines were synthesized by reaction of o-aminothiophenol with curcumin and curcuminoid β-diketones, in methanol and in acetic acid. The mechanism involves a Michael addition on the CC double bond affording a benzothiazepine with two pendant groups, an aryl group adjacent to the sulfur atom and a 1-phenylethanone adjacent to the NH of the seven membered ring. 1D and 2D multinuclear NMR (1H, 13C, 15N, 119F) in solution and 13C and 15N NMR in solid state proved to be essential to elucidate the structures of these benzothiazepines, in particular their tautomerism. A secondary product has been identified that has the structure of a benzothiazole. Keywords: curcumin; β-diketones; aminothiophenol; 1,5-benzothiazepines