Synthesis Of Benzoxazine Derivatives Catalyzed By Lewis Acid From Benzoxazoles And Propargyl Alcohols

Benzoxazines and its derivatives are important nitrogen and oxygen containing heterocyclic compounds which exist in many natural products as well as biologically and pharmaceutically active molecules.Beside this,benzoxazines are also widely used in various organic functional materials,pesticides and dyes.Consequently,considerable effort has been devoted by the synthetic organic chemistry community to the development of practical and convenient methods for the efficient preparation of functionalized benzoxazines during the past several decades.A main strategy for the benzoxazine synthesis is the cascade reaction of amines or alcohols.However,these syntheses had several drawbacks,including the use of expensive reagents as the starting materials,requiring the N-protected amines,and harsh reaction conditions.Therefore,the development of new methods for the synthesis of benzoxazines is an important research topics for organic chemists.This paper mainly focused on the synthesize N-formylbenzoxazines from benzoxazoles and propargyl alcohols catalyzed by Lewis acid.First of all,we have optimized the reaction conditions.After establishing the standard reaction conditions,the scope of this benzoxazine formation reaction was investigated by using a series of benzoxazole and propargyl alcohol derivatives.Finally,we proposed the possible reaction mechanism according to several control experiments.Simple and readily available starting materials,broad substrate scope,inexpensive Lewis acid catalyst and high atom economy make this transformation more efficient.