Oxiranyllithium based synthesis of α-keto-2-oxazolines
摘要:
alpha -Keto-2-oxazolines 5a-j have been efficiently prepared by lithiation [sec-(or n-)BuLi/TMEDA, Et2O, -100 degreesC] and rearrangement of oxiranyl oxazolines 2a-j. (C) 2000 Published by Elsevier Science Ltd.
[reaction: see text] The stereoselective synthesis of novel alpha-epoxy-beta-amino acids is described by a route that combines the chemistry of oxazolinyloxiranyllithiums with that of nitrones. The intermediate trioxadiazadispiro[2.0.4.3]undecanes 4 have been isolated and converted by hydrolysis into epoxy-5-isoxazolidinones 5 which can be transformed into the alpha-epoxy-beta-amino acids 8 by N-O
The addition reaction of alpha-lithiated oxazolinyloxiranes to nitrones has been investigated. 1,5,9-Trioxa-8,10-diazadispiro[2.0.4.3]undecanes formed in a completely diastereoselective manner upon treatment of alpha-lithiated oxiranes with nitrones. The lithiation of optically active trans and cis-oxazolinyloxiranes followed by the addition of a nitrone resulted in the formation of the same dispirocyclic compound. An explanation for the observed stereoselectivity is provided. (C) 2003 Elsevier Ltd. All rights reserved.