Nucleophilic Substitution at Quaternary Carbon Stereocenters.

Cyclopropyl carbinol derivatives undergo a regio- and stereoselective nucleophilic substitution at the quaternary carbon center, with pure inversion of configuration, to provide the acyclic products as a single diastereomer. The selectivity of the substitution is attributed to the existence of a cyclobutonium species, reacting at the most substituted carbon center. Diastereomerically pure and enantiomerically enriched tertiary alkyl bromide, chloride, ester, and fluoride could therefore be easily prepared in only three catalystic steps from commercially available alkynes.