An optical yield that increases with temperature in a photochemically induced enantiomeric isomerization

Catalytic Supramolecular Photochirogenesis

“…This is in keen contrast to the highly temperature-dependent ee values observed upon the conventional photosensitization in isotropic media, [6,32] for which the relatively rigid CD skeleton fixed by the inter-glucoside hydrogen-bonds around the secondary rim is likely to be responsible at least in part. In support of this rationalization, when photosensitization is performed by using permethylated CD derivative 4i, the skeleton of which is much more flexible due to the broken hydrogen-bonding network, the ee of 1E greatly varies with temperature to give an antipodal product.…”

Vital role of entropy in photochirogenesis

“…An unusual temperature effect upon product ee was first reported for the enantiodifferentiating Z-E photoisomerization of cyclooctene sensitized by optically active (poly)alkyl benzene(poyl)carboxylates [6] (Scheme 1). Upon photosensitization with (-)-tetramenthyl 1,2,4,5-benzenetetracarboxylate in pentane at 25 °C, (Z)-cyclooctene (1Z) smoothly isomerized to the chiral (E)-isomer (1E) in 9.6% ee in favor of (R)-enantiomer.…”

“…Indeed, a great deal of effort has been devoted to the enantio-and diastereodifferentiating photochemical reactions, which afford good to excellent enantomeric excesses (ee's) and diastereomeric excesses (de's), using diverse chiral sensitizers and auxiliaries, respectively [2][3][4]. A more intriguing phenomenon, as revealed by the mechanistic investigation of asymmetric photosensitizations is the inversion of product chirality; induced by the alteration of environmental factors such as temperature [6][7][8][9][10][11][12][13], pressure [14], solvent [15], and substrate concentration [16]. The chirality switching behavior is not only of mechanistic interest but also of particular practical importance, since such a switching enables us to control the chirality and optical yield of the photoproduct simply by maneuvering these entropy-related external factors, affording both enantiomers without using the antipodal chiral sources.…”

Temperature Dependence of Enantioselectivity in Complexations of Optically Active Phenolic Crown Ethers with Chiral Amines in Solution

“…1 However, a few papers have recently described a temperature-dependent reversal of the chirality of the enantioselectivity and a enhancement of enantiomeric recognition with increasing temperature; a temperaturedependent reversal of the elution sequence in resolution by GLC and an enhancement of the enantiomeric purities of compounds resolved with increasing column temperature 2 , improvement of the enantioselectivity of alcohol dehydrogenase-catalyzed oxidation of secondary alcohols with increasing temperature above the racemic temperature 3 and an improvement of the optical yield of the photochemically induced enantiomeric isomerization with increasing irradiation temperature. 4 We have also reported on a reversal of the sign of the ∆ R,S ∆G value for complexation of the phenolic crown ethers with neutral amines below the normal temperature and an enhancement of enantiomeric recognition with increasing temperature above the isoenantioselective temperature. 5 Enantiomeric recognition of guest compounds by complexation with optically active host compounds is helpful in developing new methods for the preparation of optically active compounds.…”

“…4 We have also reported on a reversal of the sign of the ∆ R,S ∆G value for complexation of the phenolic crown ethers with neutral amines below the normal temperature and an enhancement of enantiomeric recognition with increasing temperature above the isoenantioselective temperature. 5 Enantiomeric recognition of guest compounds by complexation with optically active host compounds is helpful in developing new methods for the preparation of optically active compounds.…”