Stereoselective Nucleophilic Halogenation at CF3-Substituted Nonclassical Carbocation.

CF3-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-CF3-motif are diastereomerically pure and can be obtained in few catalytic steps from commercially available alkynes.

Stereoselective Preparation of CF3-Containing Cyclopropanes.

A regio- and diastereoselective carbometalation of easily accessible CF3-substituted cyclopropenes is developed with a diastereoselectivity of the addition opposite to the CF3 group. This simple strategy allows the preparation of polysubstituted (up to penta-) cyclopropyl rings possessing two adjacent quaternary carbon stereocenters with excellent diastereoselectivities.