Stereoselective Electrophilic Cyclisation of O-Homoallyl Hydroxylamine Derivatives­

摘要: Electrophilic cyclisations of various O-homoallyl hydroxylamine derivatives are discussed. Non-protected hydroxylamines undergo oxidative to isoxazolines. The new isoxazoline synthesis comprises an initial electrophilic cyclisation form intermediate isoxazolidines, which subsequently oxidized Cyclisations can be conducted with electrophiles (t-BuOCl, PhSeBr, NBS and NIS). Oxidation suppressed if the starting N-sulfonylated. then provides N-sulfonylated isoxazolidines moderate cis-selectivity (up 7: 1). N-acylated isoxazolines or depending on reaction conditions (reagents). t-BuOCl-mediated affords via cyclisation, whereas NIS-induced 5-exo-cyclisation product high stereoselectivity (cis:trans = 13:1).