American Chemical Society
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Synthesis of Enantiopure Indolizinones by Cascade Ring Enlargements of 4‘-Chlorospiro[cyclopropane-1,5‘-isoxazolidines]

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posted on 2006-03-17, 00:00 authored by Julia Revuelta, Stefano Cicchi, Cristina Faggi, Sergei I. Kozhushkov, Armin de Meijere, Alberto Brandi
2-Chloro-2-cyclopropylideneacetates (1-Me and 1-Et) and their spiropentane analogues 2 cycloadd enantiopure five-membered cyclic nitrones to give the corresponding adducts (quantitatively, four examples), which undergo cascade ring enlargements to yield indolizinone derivatives (53−70%, four examples). The ring enlargement process is triggered by the abstraction of a bridgehead proton induced by a base and can be suppressed by the presence of a bulky substituent nearby, such as a (triisopropylsilyl)oxy group.