Abstract
Reaction of o-aminophenol with various maleic anhydrides gave first 2-hydroxymaleanilic acids (4-(2′-hydroxyphenylamino)-4-oxobut-2-enoic acids) (1), which were then converted into the 3-oxo-1,4-benzoxazines (2d-h) and (3f-1) under mild basic conditions; similarly the reaction of o- aminothiophenol with the maleic anhydrides gave the 3-oxo-1,4-benzothiazines (2a), (3a) and (3d) in one step. The facile cycloaddition and esterification of 2-hydroxymaleanilic acids to form the benzoxazines observed in this work is discussed in terms of the formation of the isomaleimide type intermediate (7).
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