Generation and reactivity of 3‐carbethoxy‐5‐phenyl‐ 5H,7H ‐thiazolo[3,4‐ c ]oxazol‐4‐ium‐1‐olate

3‐Carbethoxy‐5‐phenyl‐5 H ,7 H ‐thiazolo[3,4‐ c ]oxazol‐4‐ium‐1‐olate was generated from (2 R ,4 R )‐ N ‐ethoxyoxalyl‐2‐phenylthiazolidine‐4‐carboxylic acid and its reactivity studied. This münchnone showed low reactivity as dipole although from the reaction with dimethyl acetylenedicarboxylate the corresponding (3 R )‐3‐phenyl‐17 H ,3 H ‐pyrrolo[1,2‐ c ]thiazole‐5,6,7‐tricarboxylate could be isolated. The thermolysis of (2 R ,4 R )‐ N ‐ethoxyoxalyl‐2‐phenylthiazolidine‐4‐carboxylic acid in refluxing acetic anhydride led to the synthesis of N ‐(1‐ethoxycarbonyl‐2‐phenylvinyl)‐2‐phenyl‐4‐thioxo‐1,3‐thiazolidine. The structure of methyl (2 R ,4 R )‐ N ‐ethoxyoxalyl‐2‐phenylthiazoliddine‐4‐carboxylate was determined by X‐ray crystallography.