Sodium ethylcyanoacetate was found to react exclusively at the 2-position of trifluoromethanesulfonate 2-alkyl (aryl) 1, 3-oxazolinium salts 2. In most cases, the reaction leads specifically to a new series of 5-alkyl (aryl) 6-cyano 2, 3-dihydro 1, 4-oxazepine 7- ones 3. This efficient one-step ring-enlargement process occurs at the oxazolidine stage. Structural parameters affecting the scope and limitations of this condensation are ...