Enantiodifferentiating photoisomerization of 1-methylcyclooct-1-ene sensitized by chiral alkyl benzenecarboxylates: steric effects upon stereodifferentiation

Tsuneishi, Hiroshi; Hakushi, Tadao; Tai, Akira; Inoue, Yoshihisa

doi:10.1039/p29950002057

Cited by 15 publications

(16 citation statements)

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“…Similar temperature-switching behavior has recently been reported for the enantiodifferentiating Z-E photoisomerization (and subsequent thermal cyclodimerization) of homologous cycloalkenes such as 1-methylcyclooctene [10], cycloheptene [11], and cyclohexene [12]. However, it should be emphasized that such a dramatic switching of product chirality is not restricted to the unimolecular photoisomerization reactions but is also found in the bimolecular enantiodifferentiating anti-Markovnikov photoaddition of alcohol to 1,1-diphenylpropene sensitized by optically active (di)alkyl naphthalene(di)carboxylates (Scheme 2) [13].…”

Section: Temperature Switchingsupporting

confidence: 81%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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Vital role of entropy in photochirogenesis

Inoue¹,

Sugahara

Wada

2001

Pure and Applied Chemistry

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The effects of temperature, pressure, solvent, and substrate concentration upon several enantio-and diastereodifferentiating photochemical reactions have been investigated and discussed in detail. These entropy-related external factors, which manipulate the weak electronic and steric interactions in the excited state, dynamically control the stereochemical outcome of asymmetric photochemical reactions, and even switch the product chirality. A global view on the "entropy chemistry" and its potential applications are also discussed.

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Section: Temperature Switchingsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Vital role of entropy in photochirogenesis

Inoue¹,

Sugahara

Wada

2001

Pure and Applied Chemistry

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“…Photosensitization and E / Z Ratio. In previous studies concerning the enantiodifferentiating photoisomerization of cyclooctene and its derivatives, , a wide variety of optically active polyalkyl benzenepolycarboxylates were employed as chiral singlet sensitizers. Since one of the most interesting aspects of this work is the examination of the effects of the ring size and strain of ( E )-cycloalkenes on their photochemical and stereochemical behavior, we employed the same chiral sensitizers which have been extensively studied and are known to give satisfactory chemical and optical yields in the cyclooctene case, i.e., (−)-tetrabornyl, (−)-tetramenthyl, and (−)-tetrakis(8-phenylmenthyl) 1,2,4,5-benzenetetracarboxylates ( 5 − 7 ) (Scheme ) …”

Section: Resultsmentioning

confidence: 99%

Trapped Optically Active (E)-Cycloheptene Generated by Enantiodifferentiating Z−E Photoisomerization of Cycloheptene Sensitized by Chiral Aromatic Esters

Hoffmann¹,

Inoue²

1999

J. Am. Chem. Soc.

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Highly strained, optically active (E)-cycloheptene (1E) was prepared for the first time in the enantiodifferentiating geometrical photoisomerization of the (Z)-isomer (1Z) sensitized by chiral benzenetetracarboxylates at −40 to −80 °C. Low-temperature irradiations of 1Z in the presence of the chiral sensitizer, and subsequent stereospecific trapping of the optically active photoproduct, 1E, through a Diels−Alder reaction with 1,3-diphenylisobenzofuran or by oxidation with OsO4, afforded the cycloadduct or trans-1,2-cycloheptanediol, respectively. The enantiomeric excesses (ee's) of the two products were subsequently determined by chiral HPLC or GC. The ee of the product, which was used as a measure of the efficiency of chirality transfer in the excited state, was found to depend critically not only on the chiral sensitizer employed but also on the temperature and solvent employed. Thus, the ee of the product was doubled in an extreme case simply by changing the solvent from dichloromethane to hexane. Furthermore, the product chirality could be switched over a relatively narrow range of temperature as a consequence of the significant contribution of the entropy term in the enantiodifferentiating isomerization within the exciplex intermediate. Sensitization with (−)-bornyl benzenetetracarboxylate in hexane at −80 °C gave an ee value of 77%, which is the highest ee ever obtained for an asymmetric photosensitization. Based on the differential activation enthalpy and entropy for the enantiodifferentiating process and the fluorescence quenching experiments with C5−C8 cycloalkenes, the origin of the highly efficient enantiodifferentiation and a detailed mechanism for the enantiodifferentiating photoisomerizations are discussed.

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“…A comparable phenomenon has also been observed for the photoisomerization of (Z)-1-methylcyclooctene. 26 Scheme 3 Enantiodifferentiating photosensitized geometric isomerization of cycloalkenes. Activation parameters in kJ mol -1 in pentane at 298 K, unless otherwise stated.…”

Section: Entropy-driven Asymmetric Photoreactionsmentioning

confidence: 99%

Relevance of the Entropy Factor in Stereoselectivity Control of Asymmetric Photoreactions

Mori¹

2020

Synlett

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Entropy as well as enthalpy factors play substantial roles in various chemical phenomena such as equilibrium and reactions. However, the entropy factors are frequently underestimated in most instances, particularly in synthetic chemistry. In reality, the entropy factor can be in competition with the enthalpy factor or can even be decisive in determining the overall free or activation energy change upon molecular interaction and chemical transformation, particularly where weak interactions in ground and/or excited states are significant. In this account, we overview the importance of the entropy factor in various chemical phenomena in both thermodynamics and kinetics and in the ground and excited states. It is immediately apparent that many diastereo- and enantioselective photoreactions are entropy-controlled. Recent advances on the entropy-control concept in asymmetric photoreactions are further discussed. Understanding the entropy-control concept will pave the way to improve, fine-tune, and even invert the chemo- and stereoselectivity of relevant chemical phenomena.1 Introduction2 Role of Entropy in Supramolecular Interactions3 Selected Examples of Entropy-Driven Thermal Reactions4 Classical Examples of Entropy Control in Photoreactions5 Entropy-Driven Asymmetric Photoreactions6 Advances in Entropy Control7 Perspective

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Enantiodifferentiating photoisomerization of 1-methylcyclooct-1-ene sensitized by chiral alkyl benzenecarboxylates: steric effects upon stereodifferentiation

Cited by 15 publications

References 16 publications

Vital role of entropy in photochirogenesis

Vital role of entropy in photochirogenesis

Trapped Optically Active (E)-Cycloheptene Generated by Enantiodifferentiating Z−E Photoisomerization of Cycloheptene Sensitized by Chiral Aromatic Esters

Relevance of the Entropy Factor in Stereoselectivity Control of Asymmetric Photoreactions

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