Reactions of 2-aminothiphenols with chalcones in an ionic liquid medium: a chemoselective catalyst-free synthesis of 1,5-benzothiazepines

A series of 2,4-disubstituted derivatives of 1,5-benzothiazepines were prepared via a one-pot thia-Michael-cyclization sequence by the reaction of various 2-aminothiophenols with chalcones in ionic liquid media. The choice of the ionic liquid had a significant impact on the process. In the case of 1-octyl-3-methyl imidazolium thiocyanate ([omim]SCN), both steps took place in one pot to give substituted 1,5-benzothiazepines. However, only a simple thia-Michael addition could occur in 1-octyl-3-methyl imidazolium chloride ([omim]Cl) medium. Reactions were catalyst free and could tolerate the presence of different functional groups. The workup procedure was facile and the ionic liquid could be recycled at least seven times in a row.