Chemo-, regio- and stereoselective 1,3-dipolar cycloaddition of C-aryl-N-phenylnitrones over 3,5-bis(arylidene)-1-methylpiperidin-4-ones: synthesis of highly substituted novel spiro-isoxazolidines

摘要

1,3-Dipolar cycloaddition of C-aryl-N-phenylnitrones to 3,5-bis-(arylidene)-1-methylpiperidin-4-ones affords novel mono- and bis-spiroisoxazolidines in moderate yields. In general, this reaction predominantly yields mono-spiroisoxazolidine, wherein the oxygen of the nitrone is linked to the beta-carbon of the benzylidene moiety, while 3,5-bis-(2-chloro- and 3-nitro-benzylidene)-1-methylpiperidin-4-ones afford predominantly bis-spiroisoxazolidines. The cycloaddition of mono-spiroisoxazolidines occurs with facial diastereoselectivity to furnish bis-spiroisoxazolidines. The nitrogen in the heterocyclic ring of the 3,5-bis-(arylidene)-1-methylpiperidin-4-ones facilitates the cycloaddition through transannular ((NC)-C-...=O) and/or homoconjugative ((NC)-C-...=C) interactions. (c) 2006 Elsevier Ltd. All rights reserved.