Straightforward synthesis of thiazolo[5,4-]isoquinolines from dithiooxamide and 2-halobenzaldehydes

The reaction of dithiooxamide with aromatic aldehydes is a well-known method for the preparation of thiazolo[5,4- d ]thiazoles (TzTz). However, we report here that, using adequately substituted 2-halobenzaldehydes, this reaction may afford selectively thiazolo[5,4- c ]isoquinolines (TzIQ) or mixtures of TzTz and TzIQ. The use of lanthanum( iii ) triflate as the catalyst favors the formation of TzIQ. The results obtained using a large number of substituted benzaldehydes showed that the nature, number and position of halogen atoms and other substituents on the aldehyde have a great impact on the reaction outcome. The structures of six TzTz and six TzIQ were unveiled by single-crystal X-ray diffraction. Thiazolo[5,4- c ]isoquinolines, an (up to now) elusive family of compounds, are prepared in one reaction only from simple commercial reagents.