Highly Stereoselective Photocyclodimerization of a-Cyclodextrin-Appended Anthracene Mediated by γ-Cyclodextrin and Cucurbit[8]uril: A Dramatic Steric Effect Operating Outside the Binding Site

摘要

Stereochemical control through substrate encapsulation by natural and synthetic hosts is now a standard technique in both thermo-chemical and photochemical reactions. It is widely accepted that precise size/shape matching of guest substrate with the interior of the host cavity is pivotal for the critical control of reactivity and selectivity, as emphasized in currently accepted molecular recognition theories. Then, a question arises: Is it feasible to affect a reaction not by altering the matching elements of the host interior but through interactions occurring outside the cavity? In this paper, we will demonstrate that a bulky group of guest substrate located outside the host cavity can critically manipulate the stereoselectivity of photoreaction occurring inside the cavity.