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Synthesis of Halomethyl Isoxazoles/Cyclic Nitrones via Cascade Sequence: 1,2-Halogen Radical Shift as a Key Link.

Org Lett; 20(10): 2906-2910, 2018 05 18.
Artigo em Inglês | MEDLINE | ID: mdl-29707951
A novel iminoxyl radical-promoted dichotomous regioselective 5-exo-trig cyclization onto vinylic halogen/1,2-halogen radical shift sequence is developed for the synthesis of halomethyl isoxazoles/cyclic nitrones using ß-halo-ß,γ- and γ-halo-γ,δ-unsaturated ketoximes as the substrates and PhI(OAc)2/TEMPO as the oxidation system. DFT calculations reveal that a halogen-bridged three-membered ring transition state is involved in the 1,2-Cl-/Br-atom shift, while the 1,2-I atom migration can be taken into account with an elimination/readdition mechanism. The migration ability was indicated to be ranked in the following order: I > Br > Cl.