A new route to 3,5-disubstituted isoxazolidines via the iodocyclization of homoallylic hydroxylamines
摘要:
N,N-Dialkyl-O-trialkylsilyl homoallylic hydroxylamines reacted with iodine, N-iodosuccinimide, or iodine chloride to give 3,5-disubstituted isoxazolidines in good yield. The relative configuration that was generated at C3 and C5 was controlled by the nature of the nitrogen substituent of the parent hydroxylamine: the presence of a primary alkyl group favored the formation of a cis-isoxazolidine, whereas the presence of a tert-butyl group favored the formation of a trans-isoxazolidine. The effects that the N- and O-substituents and the nature of the iodinating agent exerted on the stereoselectivity of the cyclization were examined. The synthesis of enantiomerically pure isoxazolidines from hydroxylamines carrying a chiral N-mannofuranosyl group is described.
A new route to 3,5-disubstituted isoxazolidines via the iodocyclization of homoallylic hydroxylamines
摘要:
N,N-Dialkyl-O-trialkylsilyl homoallylic hydroxylamines reacted with iodine, N-iodosuccinimide, or iodine chloride to give 3,5-disubstituted isoxazolidines in good yield. The relative configuration that was generated at C3 and C5 was controlled by the nature of the nitrogen substituent of the parent hydroxylamine: the presence of a primary alkyl group favored the formation of a cis-isoxazolidine, whereas the presence of a tert-butyl group favored the formation of a trans-isoxazolidine. The effects that the N- and O-substituents and the nature of the iodinating agent exerted on the stereoselectivity of the cyclization were examined. The synthesis of enantiomerically pure isoxazolidines from hydroxylamines carrying a chiral N-mannofuranosyl group is described.
The trimethylsilyl triflate promoted allylation of nitrones with allyltributylstannane affords O-silylated hydroxylamines in high yield; when the crude reaction mixture is quenched with N-iodosuccinimide, 5-iodomethylisoxazolidines are formed in excellent yields. The overall one-pot two-step process represents a valuable improvement in terms of time, cost and overall yield with respect to the previously reported three stage procedure involving nitrone allylation, hydroxylamine O-silylation, and iodocyclisation. (C) 1998 Elsevier Science Ltd. All rights reserved.
MANCINI, FABRIZIO;PIAZZA, MARIA GIULIA;TROMBINI, CLAUDIO, J. ORG. CHEM., 56,(1991) N3, C. 4246-4252
作者:MANCINI, FABRIZIO、PIAZZA, MARIA GIULIA、TROMBINI, CLAUDIO