Stereoselective Nucleophilic Halogenation at CF 3 -Substituted Nonclassical Carbocation.

CF 3 -substituted cyclopropyl carbinol derivatives undergo regioselective and diastereoselective nucleophilic halogenation at the quaternary carbon center to provide acyclic products as a single diastereomer. The selectivity of the substitution is rationalized by the formation of a nonclassical cyclopropylcarbinyl cation intermediate, reacting at the most-substituted carbon center. Tertiary alkyl chlorides, bromides, and fluorides adjacent to a stereogenic C-CF 3 -motif are diastereomerically pure and can be obtained in few catalytic steps from commercially available alkynes.