“…As an exception, formaldehyde reacted to give 5,5′‐methanediylbis(4‐hydroxy‐2‐aryl‐6 H ‐1,3‐thiazin‐6‐ones), just as it was previously shown by Ziegler , and no further cyclization was observed upon its heating in various conditions (py, DMF, THF, and AcOH). The other exception was salicylaldehyde, and by virtue of 2‐hydroxygroup, it reacts with thiazines 4 to give coumarin derivatives, as we have shown previously .…”