Alkyne‐Assisted Stereospecific Skeletal Rearrangement via Nonclassical Carbocations

We report stereospecific nucleophilic substitutions of homopropargylic alcohols enabled by anchimeric assistance from an alkyne. Upon activation, neighboring‐group participation of the alkyne generates a nonclassical cyclopropylidenemethyl cation. The transformation provides access to densely‐substituted tertiary homopropargyl fluorides with broad functional‐group tolerance and efficient chirality transfer from enantioenriched alcohols. Computational studies support the involvement of the nonclassical cationic intermediate. The calculations further indicate that alkyne‐derived nonclassical cations are less stabilized than their alkene analogues.