Electrophilic Spirocyclization of a 2‐Biphenylacetylene via Conformational Fixing within a Hollow‐Cage Host

Abstract

Abstract A 2‐biphenylacetylene was fixed into a specific conformation within the confined cavity of a hollow cage, where it underwent a regioselective spirocyclization in the presence of an electrophile. A 5‐ endo ‐ dig cyclization proceeded selectively in the cage, which stands in sharp contrast to the 6‐ endo ‐ dig cyclization that normally occurs in common organic media. The folded conformation adopted by the substrate within the cage was examined by 1 H NMR spectroscopy and X‐ray crystallographic analysis.