Proton‐Promoted Hydroamination of 3‐Dialkylthiomethylene‐1,4‐pentadiynes with o‐Phenylenediamines: A Facile Route to Benzo[b][1,4]diazepines

The first proton-promoted intermolecular hydroamination reaction of the enynes, a,a-dialkynylketene S,S-acetals 2, is described. A series of benzo[b][1,4]diazepines, with the structures of 3 and 5, were prepared chemo- and regioselectively in good to high yields by reacting the readily available 1,4-diynes 2 with both terminal and internal alkyne functions with o-phenylenediamines under very mild conditions.