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Synthesis and Characterization of β-Haloalkenyl-λ3-bromanes:  Stereoselective Markovnikov Addition of Difluoro(aryl)-λ3-bromane to Terminal Acetylenes

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posted on 03.08.2005, 00:00 authored by Masahito Ochiai, Yoshio Nishi, Takeshi Mori, Norihiro Tada, Takashi Suefuji, Hermann J. Frohn
Reported here for the first time are the synthesis, isolation, and characterization of hypervalent β-haloalkenyl-λ3-bromanes. Exposure of terminal alkynes to p-trifluoromethylphenyl(difluoro)-λ3-bromane activated by BF3-i-Pr2O resulted in fluoro-λ3-bromanation of the triple bonds in a Markovnikov fashion, yielding (E)-β-fluoroalkenyl-λ3-bromanes stereoselectively in good yields. 5-Chloro-1-pentynes undergo domino λ3-bromanation−chlorine shift−fluorination or λ3-bromanation−chlorine shift−alkyl shift−fluorination reaction, depending on the substituents and afford (E)-β-chloroalkenyl-λ3-bromanes stereoselectively in high yields. The β-chloroalkenyl-λ3-bromanes contain three kinds of halogen atoms, F, Cl, and Br, in the molecule.

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