Syntheses of (RS)-homoibotenic acid and (RS)-4-bromohomoibotenic acid. An unusual Michael type reaction and isoxazole deprotection

Abstract
Addition of ammonia to (E)-3-methoxyisoxazole-5-propenoic acid with concurrent Lewis acid induced deprotection yields (RS)-α-amino-3-hydroxyisoxazole-5-propionic acid (homoibotenic acid), which was independently synthesized by an unambiguous route also used for the preparation of (RS)-α-amino-3-hydroxy-4-bromoisoxazole-5-propionic acid.