Lewis Acid-Mediated Efficient Synthesis of 4H-1,3-benzo-xazines and Their Derivatives 4,5-dihydro-1,3-benzo-xazepines

: Compounds containing 4H-1,3-benzo-xazine core usually possess characteristic features and have been applied in the fields of organic synthesis, pharmaceutical research, materials science and bioscience. Here we reported convenient and direct access to 4H-1,3- benzo-xazines and their derivatives through intramolecular cyclization of olefinic amides or ureas with good to excellent yields in the presence of TMSOTf. The properties (mild conditions, metal or additives-free, wide substrate scope and functional group tolerance) of the process made it a promising strategy to synthesize various benzo-xazines and their derivatives.