Isocyano(triphenylphosphoranylidene)acetates: Key to the One-Pot Synthesis of Oxazolo[4,5-c]quinoline Derivatives via a Sequential Ugi/Wittig/aza-Wittig Cyclization Process

A one-pot novel strategy is described for the construction of various oxazolo[4,5-c]quinoline derivatives starting from the isocyano(triphenylphosphoranylidene)-acetates, aldehydes, amines, and 2-azidobenzoic acids. The reactions generated the target products directly in moderate to good yields via a sequential Ugi/Wittig/aza-Wittig cyclization process. The salient features of the method are that all three groups of the multifunctional isocyanides were involved in the reaction with broad substituent scopes and mild reaction conditions, making the protocol a useful contribution to the synthesis of oxazolo[4,5-c]quinoline heterocycles.