An intriguing effect of Yb(OTf)3–TMSCl in the halogenation of 1,1-disubstituted alkenes by NXS: selective synthesis of allyl halides

A novel protocol to effect the efficient selective halogenation of 1,1-disubstituted alkenes with NXS catalyzed by Yb(OTf)3–TMSCl, which affords the corresponding allyl halides in high yield, including allyl bromide, chloride, iodide and fluoride, is described. A remarkable feature of Yb(OTf)3–TMSCl-catalyzed halogenation is that, unlike conventional radical halogenation with N-halosuccinimides, the reaction discriminates between the allylic and benzylic positions. The reaction occurs selectively at the allylic position to give allylic halides, but not at the benzylic position.