Studies on the Occurence of Hydrogen Transfer, 58. ‐ Possibilities and Limits of Photochemically Induced Asymmetric Synthesis

Horner, L.

doi:10.1002/jlac.197919790816

Cited by 37 publications

(14 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The Arrhenius treatment of each quenching rate constant leads to eqn. (8). A plot of In (E/Z)pss vs. l/Tgives an excellent straight line for each sensitizer as shown in Fig.…”

Section: Photostationary State E : 2 Ratios [(E/z)jmentioning

confidence: 66%

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

Tsuneishi¹,

Hakushi²,

Tai³

et al. 1995

J. Chem. Soc., Perkin Trans. 2

View full text Add to dashboard Cite

“…The Arrhenius treatment of each quenching rate constant leads to eqn. (8). A plot of In (E/Z)pss vs. l/Tgives an excellent straight line for each sensitizer as shown in Fig.…”

Section: Photostationary State E : 2 Ratios [(E/z)jmentioning

confidence: 66%

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

Tsuneishi¹,

Hakushi²,

Tai³

et al. 1995

J. Chem. Soc., Perkin Trans. 2

View full text Add to dashboard Cite

“…[4,5] The few reported studies were discouraging,a nd enantioselectivities did not exceed 20 % ee. [6] With the advent of efficient hydrogen-bonding templates and catalysts, [7] it became evident, however,t hat the issue of insufficient enantioface differentiation could be overcome,a nd the first highly enantioselective triplet-sensitized reaction was disclosed in 2009. [8] Am odified version of the xanthone catalyst used in this and related studies [9] was presented in 2014 and was based on at hioxanthone as the sensitizing unit.…”

mentioning

confidence: 99%

Enantioselective Visible‐Light‐Mediated Formation of 3‐Cyclopropylquinolones by Triplet‐Sensitized Deracemization

et al. 2019

View full text Add to dashboard Cite

3-Allyl-substituted quinolones undergo at ripletsensitized di-p-methane rearrangement reaction to the corresponding 3-cyclopropylquinolones upon irradiation with visible light (l = 420 nm). Ac hiral hydrogen-bonding sensitizer (10 mol %) was shown to promote the reaction enantioselectively (88-96 %y ield, 32-55 %e e). Surprisingly,i tw as found that the enantiodifferentiation does not occur at the state of initial product formation but that it is the result of aderacemization event. The individual parameters that control the distribution of enantiomers in the photostationary state have been identified.Triplet sensitization represents an efficient and elegant way to promote amolecule from its ground state to atriplet state, in most cases to the lowest-lying triplet state T 1 .T he mechanism of the process has been elucidated, [1] and apart from an energetic driving force,itiscrucial that the sensitizer and the substrate are in close spatial proximity to allow for efficient sensitization. Thei dea to employ triplet energy transfer by ac hiral sensitizer and to perform photochemical reactions enantioselectively was first disclosed in the 1960s. Pioneering studies were directed to the formation of chiral trans-1,2-diphenylcyclopropane (1)from its racemate (rac-1). After initial work by Hammond with as ensitizer that was later shown to operate on the singlet hypersurface, [2] Ouanns and co-workers found in 1973 that chiral ketone 2 induced an otable but small enantioselectivity (3 % ee)i nt he formation of 1 (Scheme 1). [3] Thee fficiency of the reaction suffered from the simultaneous formation of the achiral cyclopropane 3.In the 1980s and 1990s,l ittle attention was paid to the topic of enantioselective triplet-sensitized reactions. [4,5] The few reported studies were discouraging,a nd enantioselectivities did not exceed 20 % ee. [6] With the advent of efficient hydrogen-bonding templates and catalysts, [7] it became evident, however,t hat the issue of insufficient enantioface differentiation could be overcome,a nd the first highly enantioselective triplet-sensitized reaction was disclosed in 2009. [8] Am odified version of the xanthone catalyst used in this and related studies [9] was presented in 2014 and was based on at hioxanthone as the sensitizing unit. [10] Thec ompound, which is available in both enantiomeric forms 4 ( Figure 1) [11] and ent-4,has the advantage to operate with visible light and holds promise to be av ersatile catalyst for several photochemical reactions. [12,13] In the current study,weattempted to use catalyst 4 in an enantioselective [14] di-p-methane rearrangement reaction [15] of 3-allyl-substituted quinolones.A lthough the enantioselectivities of the reaction remained moderate,the mode of action turned out to be remarkable.I tw as found that the enantioenriched cyclopropanes are formed in ad eracemization process,w hich resembles the seminal work on chiral cyclopropanes [2,3] (see Scheme 1), and which likely proceeds via a1 ,3-diradical intermediate.T he results of our preliminary exper...

show abstract

“…Based on the low triplet energy (E T ) of trans-1,2diphenylcyclopropane (rac-7, Scheme 1), which is approximately 220 kJ mol À1 , ketone 21 was used for the enantioselective E/Z isomerization of trans-1,2-diphenylcyclopropane by Ouanns et al in 1973. [35,36] However, the enantioselectivity was not higher (with a maximum ee of 3 %) than in the case of singlet sensitization (Scheme 1).…”

Section: Ketonesmentioning

confidence: 89%

Enantioselective Catalysis of Photochemical Reactions

et al. 2015

View full text Add to dashboard Cite

The nature of the excited state renders the development of chiral catalysts for enantioselective photochemical reactions a considerable challenge. The absorption of a 400 nm photon corresponds to an energy uptake of approximately 300 kJ mol(-1) . Given the large distance to the ground state, innovative concepts are required to open reaction pathways that selectively lead to a single enantiomer of the desired product. This Review outlines the two major concepts of homogenously catalyzed enantioselective processes. The first part deals with chiral photocatalysts, which intervene in the photochemical key step and induce an asymmetric induction in this step. In the second part, reactions are presented in which the photochemical excitation is mediated by an achiral photocatalyst and the transfer of chirality is ensured by a second chiral catalyst (dual catalysis).

show abstract

Studies on the Occurence of Hydrogen Transfer, 58. ‐ Possibilities and Limits of Photochemically Induced Asymmetric Synthesis

Cited by 37 publications

References 26 publications

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

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

Enantioselective Visible‐Light‐Mediated Formation of 3‐Cyclopropylquinolones by Triplet‐Sensitized Deracemization

Enantioselective Catalysis of Photochemical Reactions

Contact Info

Product

Resources

About