Supramolecular Complexation and Enantiodifferentiating Photocyclodimerization of 2-Anthracenecarboxylic Acid with 4-Aminoprolinol Derivatives as Chiral Hydrogen-Bonding Templates

Abstract

The photochirogenesis of 2-anthracenecarboxylic acid (AC) complexed to a hydrogen-bonding template (TKS159) was investigated to obtain mechanistic information on how chirogenesis is achieved for the dimerization of AC. Complexation of AC to TKS159 leads to the shielding of one of the two surfaces of the prochiral AC molecule. The two diastereomeric AC-TKS complexes, i.e., re-AC-TKS and si-AC-TKS, were characterized by changes in the UV-vis, fluorescence, and circular dichroism spectra and excited-state lifetimes. The ee is not simply determined by the diastereomeric ratio of the re- and si-AC-TKS complexes but also depends on the relative lifetimes of the diastereomeric complexes. The relative population of the re and si complexes was calculated from the enantiomeric excess (ee) for the products, taking into account the relative lifetimes of the two complexes. These studies established a protocol that can be used to reveal the mechanism for photochirogenesis by investigating the ground state and the excited state behavior of supramolecular systems.

Catalytic Supramolecular Photochirogenesis

“…Of the many weak non-covalent interactions, the hydrogen-bonding interaction, which is Brought to you by | MIT Libraries Authenticated Download Date | 5/10/18 6:58 PM strong and directional, is most frequently employed as a tool for capturing the guest substrate and controlling its orientation, configuration and/or conformation in the supramolecular complex formed. [55,56] Multiple hydrogen-bonding interactions provided by chiral templates can also confine and preorganize substrate(s) to drive photoreactions towards the specific stereochemistry desired. [57][58][59] Bach et al have developed a series of Kemp's acidbased chiral templates, such as 32 and 33, which possess a lactam moiety as a hydrogen-bond donor/acceptor, and an aromatic moiety as both a built-in photosensitizer and a fence to shield one of the enantiotopic faces of an amidecarrying prochiral substrate bound to the template.…”

Effects of Temperature and Host Concentration on the Supramolecular Enantiodifferentiating [4 + 4] Photodimerization of 2-Anthracenecarboxylate through Triplet-Triplet Annihilation Catalyzed by Pt-Modified Cyclodextrins

“…Supramolecular photochirogenesis provides a promising solution to such problems, as “confined space” for the prochiral substrate(s) was created before photoexcitation through the much longer and more intimate supramolecular interactions at both ground and excited states. A variety of chiral hosts, such as cyclodextrin derivatives [2,3,4,5,6,7,8,9,10,11,12,13,14,15], chiral hydrogen-bonding templates [16,17,18,19], chiral macrocyclic molecules [20,21] and biological macromolecules [22,23], have been developed and utilized as chiral sources for efficient photochirogenic control. However, an excess amount of chiral host is demanded in most supramolecular photochirogenesis for the purpose of inhibiting the undesired racemic photoproduct resulting from the photoreaction of the uncomplexed photosubstrates in the bulk solution [24].…”

Absolute configuration determination of theanti-head-to-head photocyclodimer of anthracene-2-carboxylic acid through cocrystallization withL-prolinol

“…We have recently assigned the absolute configurations of the chiral syn-head-to-tail (syn-HT) and anti-head-to-head (anti-HH) cyclodimers ( Fig. 1) of anthracene-2-carboxylic acid (AC) through comparison of the theoretical versus experimental circular dichroism (CD) spectra (Wakai et al, 2012), which are crucial in elucidating the enantiodifferentiation mechanism of AC photocyclodimerization mediated by chiral supramolecular hosts, such as hydrogen-bonding templates (Mizoguchi et al, 2006;Kawanami et al, 2009), cyclodextrins Qui et al, 2009;Yang et al, 2011) and serum albumins (Wada et al, 2003;Nishijima et al, 2007). The theoretical CD spectra calculated using the state of the art RI-CC2 method reproduced, nearly perfectly, the experimental CD spectrum of the syn-HT dimer but showed appreciable deviations in the relative intensities of the major CD extrema for the anti-HH dimer, although the signs and alternating pattern of the experimental Cotton effects were reproduced satisfactorily.…”