Copper-Mediated Domino Cyclization/Trifluoromethylation of Propargylic N-Hydroxylamines: Synthesis of 4-Trifluoromethyl-4-isoxazolines.

A Cu(OTf)2-mediated synthesis of trifluoromethylated 4-isoxazolines is described. In one step from readily available propargylic N-hydroxylamines, a domino 5-endo-dig cyclization, followed by trifluoromethylation, takes place to construct the 4-isoxazoline core with concomitant installation of the CF3 group at the C-4 position. Such compounds could also be useful precursors for the preparation of α-trifluoromethyl β-amino ketones.