Catalytic Supramolecular Photochirogenesis

Abstract

Supramolecular photochirogenesis is a new strategy for circumventing the inherent difficulties encountered in conventional photochirogenesis, i.e. the interactions associated with geometrically less-defined, short-lived excited states, by confining a prochiral substrate(s) in a chiral supramolecular environment(s) prior to photoexcitation. This rather simple, but very successful, strategy has been applied to a variety of chiral photoreactions. However, a stoichiometric, or even excess amount of supramolecular host is often needed to ensure full complexation of the substrate, and achieve the optimum stereochemical outcome. This apparent drawback has recently been removed by introducing a sensitizing moiety to the supramolecular host, or by bathochromically shifting the absorption band of substrate through Lewis acid, or charge-transfer complexation. Recent progress in catalytic supramolecular photochirogenesis will be reviewed.

Excited-State Dynamics Achieved Ultimate Stereocontrol of Photocyclodimerization of Anthracenecarboxylates on a Glucose Scaffold

“…Simultaneously achieving high chemical and optical yields in chiral photoreactions has long been an important goal for photo- and synthetic chemists . Indeed, a number of diastereodifferentiating photoreactions, using diverse chiral auxiliaries and scaffolds, were examined and several of them have been employed in the syntheses of crucial chiral components of bioactive natural products. , Nevertheless, the high diastereomeric excesses (de’s) reported are often accompanied by modest chemical yields, which is in contrast to the success in thermal asymmetric syntheses using chiral catalysts and enzymes .…”

“…Simultaneously achieving high chemical and optical yields in chiral photoreactions has long been an important goal for photo- and synthetic chemists . Indeed, a number of diastereodifferentiating photoreactions, using diverse chiral auxiliaries and scaffolds, were examined and several of them have been employed in the syntheses of crucial chiral components of bioactive natural products. , Nevertheless, the high diastereomeric excesses (de’s) reported are often accompanied by modest chemical yields, which is in contrast to the success in thermal asymmetric syntheses using chiral catalysts and enzymes . For instance, moderate–high diastereoselectivities were reported for the photocyclization of diarylethenes (28–100% de), the photoisomerization of cyclooctene (21–43% de), the photocyclodimerization of cinnamates (46–97% de), the photocycloaddition of enones to olefins (56–91% de), and the Paternò–Büchi reaction of ketones with olefins (7–97%), but high chemical yields have rarely been achieved simultaneously.…”

Photocatalytic Supramolecular Enantiodifferentiating Dimerization of 2-Anthracenecarboxylic Acid through Triplet–Triplet Annihilation

“…This significantly limits the application of the supramolecular photochirogenesis, especially considering that chiral hosts are often not readily accessible. Catalytic photoreactions have been realized by strategies, such as triplet sensitization, photoinduced electron transfer, selective photoexcitation of complexes, and photoredox catalysis . However, very few have been applied to supramolecular photochirogenesis.…”

Chiral Photocatalyst Structures in Asymmetric Photochemical Synthesis

“…Polar protic solvents that weaken these non-covalent interactions often result in lower enantioselectivities. ,,− An alternate strategy that has been studied for asymmetric photocatalysis involves the use of macromolecular systems that encapsulate (or include ) small organic molecules and subsequently alter the outcomes of their reactions. Several excellent reviews on this topic have been published. ,,− …”