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

Abstract

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.