The application of a domino radical bicyclization for
the synthesis
of compounds containing the 1-azaspiro[4.4]nonane skeleton in 11–67%
yields as a mixture of diastereomers is described (trans configuration preference). This process involved formation and capture
of alkoxyaminyl radicals. For this purpose, O-benzyl
oxime ethers with a brominated or iodinated aromatic ring or a terminal
alkynyl group and an alkenyl moiety were employed as starting materials.
The bicyclization was initiated by 2,2′-azobisisobutyronitrile
or triethylborane and promoted by Bu3SnH. The best results
were obtained with O-benzyl oxime ethers containing
an alkenyl moiety tethered to electron withdrawing groups or aryl
substituents, whereas oxime radical precursor attached to methyl-substituted
olefin precluded the capture of alkoxyaminyl radical, giving rise
mainly to monocyclized product.
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