A Divergent and Selective Synthesis of Isomeric Benzoxazoles from a Single N–Cl Imine.

A divergent and regioselective synthesis of either 3-substituted benzisoxazoles or 2-substituted benzoxazoles from readily accessible ortho-hydroxyaryl N–H ketimines is described. The reaction proceeds in two distinct pathways through a common N–Cl imine intermediate: (a) N–O bond formation to form benzisoxazole under anhydrous conditions and (b) NaOCl mediated Beckmann-type rearrangement to form benzoxazole, respectively. The reaction path also depends on the electronic nature of the aromatic ring, with the electron-rich aromatic rings favoring the rearrangement and the electron-deficient rings favoring the N–O bond formation. A Beckmann-type rearrangement mechanism vianet [1,2]-aryl migration for the formation of 2-substituted benzoxazole is proposed. [ABSTRACT FROM AUTHOR]