Temperature switching of product chirality upon photosensitized enantiodifferentiating cis-trans isomerization of cyclooctene

Vital role of entropy in photochirogenesis

“…Equation 1 indicates that the logarithm of k S /k R is proportional to reciprocal temperature, and that the activation parameters (∆∆H ‡ S-R and ∆∆S ‡ S-R ) can be calculated from the slope and intercept of the ln(k S /k R )-versus-1/T plot. Hence, the enantiodifferentiating photoisomerization of 1Z sensitized by a variety of chiral sensitizers was performed at several temperatures to give 1E in varying ee's, and the ln(k S /k R ) value was plotted against the reciprocal temperature to give an excellent straight line for each sensitizer [6][7][8][9]. Typical absolute ∆∆H ‡ S-R and T∆∆S ‡ S-R values obtained for non-ortho sensitizers are <0.1 and <0.2 kcal•mol -1 , respectively, while those for ortho sensitizers are as high as 0.5-1.1 and 0.5-3.5 kcal•mol -1 , respectively.…”

“…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.…”

Unusual CD couplet pattern observed for the π*←n transition of enantiopure (Z)‐8‐methoxy‐4‐cyclooctenone: An experimental and theoretical study by electronic and vibrational circular dichroism spectroscopy and density functional theory calculation

“…[1][2][3][4][5] It is known that chiral (E)-cyclooctene is produced in moderate to high enantiomeric excess through the diastereomeric interaction in the intervening exciplex of chiral sensitizer with the prochiral substrate, that is, (Z)-cyclooctene. 6 (Z)-and (E)-isomers of substituted cyclooctenes show relatively large anisotropy factors (g) in their circular dichroism (CD) spectra in the ultraviolet-visible (UV-vis) region, 7 which is useful for absolute asymmetric synthesis using circularly polarized light.…”

Chirality effects in gas-phase spectroscopy and photophysics of molecular and ionic complexes: contribution of low and room temperature studies

“…Most of the observed selectivity rests on enantiodifferentiation in the ground state, through enantioselective contact pair formation, or through hydrogen bonding of the photochemically produced intermediate with an optically active agent [257,258,260]. In some cases, enantioselectivity is explained in terms of formation of exciplex or triplex involving enantioselective interactions [261,262]. Less is known in the gas phase and the enantioselectivity of photophysical processes like inter-system crossing, photo-induced charge transfer and photodissociation in isolated systems will be discussed in what follows.…”