A High Yield Procedure for the Preparation of 2-Hydroxynitrostyrenes: Synthesis of Imines and Tetracyclic 1,3-Benzoxazines

Attempts to synthesize 2-hydroxynitrostyrenes by a Knoevenagel condensation of salicylaldehyde and subsequent elimination were unsuccessful because of the formation of a stable imine. This could be easily prevented by using secondary amines to catalyze the reaction, which then afforded 2-hydroxynitrostyrenes in high yields. In addition, the stable imine that was formed by employing ammonium acetate underwent a reaction with phosgene to allow the preparation of benzoxazines in good yields.