Dynamic Figure Eight Chirality: Multifarious Inversions of a Helical Preference Induced by Complexation
We demonstrate two types of inversion of a helical preference upon the 1:1 complexation of a dynamic figure eight molecule with a guest molecule through the controlled transmission of point chirality. We designed a series of macrocycles that prefer a nonplanar conformation with figure eight chirality. These macrocycles are composed of a chirality-transferring unit (terephthalamide) and a structure-modifying unit (two o-phenylene rings spaced with a varying number of triple bonds). The former unit provides a binding site for capturing a guest molecule through the formation of hydrogen bonds. The attachment of chiral auxiliaries to the former unit induces a helical preference for a particular sense through the intramolecular transmission of point chirality. For relatively small-sized macrocycles, the preferred sense was reversed upon complexation with an achiral guest. Contrary preferences before and after complexation were both seen for chiral auxiliaries associated with a figure eight host through two-way intramolecular transmission of the single chiral source. Alternatively, the helical preference induced in relatively large-sized macrocycles was reversed only when a figure eight host formed a 1:1 complex with a particular enantiomeric guest through the supramolecular transmission of point chirality in the guest. This stereospecific inversion of a helical preference is rare.
A versatile synthetic route to dehydrobenzoannulenes via in situ generation of reactive alkynes
This paper outlines the development of a protocol that allows in situ generation of unstable alkynes under Pd-catalyzed cross-coupling conditions. Cu-mediated intramolecular cyclization of the resultant α,ω-polyynes provides dehydrobenzoannulenes as singular species, in very good overall yields, and in a variety of topologies that are inaccessible by traditional routes or previously available in low yield only. In addition, we will discuss the solid-state structure and reactivity of these macrocycles, as well as the ability of the planar dehydrobenzoannulenes to support weak induced ring currents.
Bell, Michael L,Chiechi, Ryan C,Johnson, Charles A,Kimball, David B,Matzger, Adam J,Brad Wan,Weakley, Timothy J.R,Haley, Michael M
p. 3507 - 3520
(2007/10/03)
Versatile synthetic route to and DSC analysis of dehydrobenzoannulenes: Crystal structure of a heretofore inaccessible [20]annulene derivative
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Haley,Bell,English,Johnson,Weakley
p. 2956 - 2957
(2007/10/03)
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