[Structure: see text] Supramolecular enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid (AC) was performed in the presence of (2S,4S)-4-amino-5-chloro-2-methoxy-N-(1-ethyl-2-hydroxymethyl-4-pyrrolidinyl)benzamide (TKS159), and its stereoisomers were employed as chiral templates. The TKS template provides us with a novel hydrogen-bonding and shielding motif for enantioface-selectively binding an AC molecule. Chiral products 2 and 3 were obtained in good enantiomeric excesses (ee's) of 40% and 40%, respectively.

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.

An unprecedented 2:2 complex was shown to intervene in the enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid (A) mediated by a hydrogen-bonding template l-prolinol (P) to accelerate the formation of chiral anti-head-to-head and achiral syn-head-to-head cyclodimers in >99% combined yield with enhanced enantioselectivities of up to 72% ee for the former. The supramolecular complexation and photochirogenic behaviors, as well as the plausible structures, of intervening Am·Pn complexes (m, n = 1 or 2) were elucidated by combined theoretical and experimental spectroscopic, photophysical, and photochemical studies. Furthermore, the photochemical chiral amplification was achieved for the first time by utilizing the preferential 2:2 complexation of A with homochiral P to give normalized product enantioselectivities higher than those of the template used. The present strategy based on the higher-order hydrogen-bonding motif, which is potentially applicable to a variety of carboxylic acids and β-aminoalcohols, is not only conceptually new and expandable to other (photo)chirogenic and sensing systems but also may serve as a versatile tool for achieving photochemical asymmetric amplification and constructing chiral functional supramolecular architectures.

Near-perfect stereoselectivity was attained in the diastereodifferentiating [4 + 4] photocyclodimerization of 2-anthracenecarboxylates tethered to a glucose scaffold not by thermodynamically tuning the conformer equilibrium in the ground state but by kinetically controlling the conformer dynamics and reactivity in the excited state, which enabled us, after removal of the scaffold, to obtain a single enantiomer of chiral anti-head-to-head-cyclodimer in >99% optical and 96% chemical yield from an ensemble of four precursor conformers.