A divergent and selective synthesis of isomeric benzoxazoles from a single N-Cl imine |
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Authors: | Chen Cheng-yi Andreani Teresa Li Hongmei |
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Institution: | Process Chemistry, Merck Research Laboratories, P.O. Box 2000, Rahway, New Jersey 07065, USA. cheng_chen@merck.com |
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Abstract: | 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 via net 1,2]-aryl migration for the formation of 2-substituted benzoxazole is proposed. |
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