Supramolecular Photochirogenesis with a Higher-Order Complex: Highly Accelerated Exclusively Head-to-Head Photocyclodimerization of 2-Anthracenecarboxylic Acid via 2:2 Complexation with Prolinol

Abstract

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.

Green light triggered [2+2] cycloaddition of halochromic styrylquinoxaline—controlling photoreactivity by pH

“…Furthermore, incorporating a pH switch into a photoreactive system as an additional feature to lock/unlock its photo-reactivity, coupled with long wavelength visible light activation, offers fascinating possibilities for the construction of molecular switches in nanotechnology-based applications 23 , and the assembly of chiral functional supramolecular architectures. For example, the enantiodifferentiating [4+4] photocycloaddition of 2-anthracenecarboxylic can be controlled by complexation with a template, via hydrogen-bonding, and the formation of specific enantiomers can be accelerated by tuning pH of the environment [24][25][26][27] . In biochemistry, the photo-behaviors of amino acids, such as racemization and decomposition, is strongly dependent on the pH of the environment and this feature has been utilized in the enantioenrichment of biologically important molecules, such as meteorite born amino acids 28,29 .…”

Chiral thiophene derivatives with optimal two‐photon absorption in near‐infrared window I and II

“…As shown in Figure , three thiophene derivatives are designed by utilizing three chiral amino acid pendants (cinchonidine, phenylalaninol, and prolinol) to modify the thiophene core, which are abbreviated as thiophene‐ A, ‐B and –C. The three amino acid pendants are chosen for their strong chirality, low cost and feasibility of linking to the thiophene molecules . Additionally, different fluorine atom substituent numbers are employed in the three derivatives to further manipulate molecular TPA.…”

Near perfect head-to-head selectivity on the supramolecular photocyclodimerisation of 2-anthracenecarboxylate with self-organised gemini surfactant bilayers

“…Most of the high HH selectivities are reported for the photocyclodimerisations conducted in solid state or in organic solvents at low temperatures. 12,17,24 Yang et al…”

“…Ever since the first report in 1867, [1][2][3] the [4+4] photocyclodimerisation of anthracene and its derivatives has attracted much attention due to the unique structure and properties of the photocyclodimers obtained, and has been employed indeed as a key motif in energy storage and photoreversible devices. [4][5][6][7][8] However, controlling regioand enantioselectivities of the photocyclodimerisation of anthracene derivatives, such as 2-anthracenecarboxylate (AC) (Scheme 1), is a challenge, which has driven researchers to the use of supramolecular approach, 9,10 using cyclodextrins, [11][12][13][14] proteins, 15,16 molecular templates, [17][18][19][20][21] molecular cages, [20][21][22] twisted self-associated templates, 18 organogels, 23 and helical metal nanostructures 24 as hosts and templates. Most of the reported systems, however, require the multi-step synthesis of host/template, the modification of guest substrate and/or the irradiation in organic media at low temperature.…”