Diphenylphosphoryl Azide (DPPA)‐Mediated One‐Pot Synthesis of Oxazolo[4,5‐ c ][1,8]naphthyridin‐4(5 H )‐ones, Oxazolo[4,5‐ c ]quinoline‐4(5 H )‐ones, and Tosyloxazol‐5‐yl Pyridines

An operationally facile and efficient protocol has been developed for the construction of various 1,3‐oxazole‐containing heterocycles with excellent yields of up to 94 %. This protocol proceeds through a diphenylphosphoryl azide (DPPA)‐mediated reaction cascade on substituted 2‐aminonicotinic acids/2‐aminoanthranilic acids with ethyl isocyanoacetate/ p ‐toluenesulfonylmethyl isocyanides by forming C−C, C−O, and C−N bonds in a single operation. The synthetic utility of this transformation is also extended through a scaled‐up synthesis and C−H activation. The salient features such as metal‐free, mild reaction conditions, higher yields, and clean reactions make the protocol a useful contribution to the synthesis of medicinally useful heterocycles.