Memory of chirality in photochemistry

Angewandte Chemie - International Edition

Volumn 38, Issue 17, 1999, Pages 2586-2587

  Giese, Bernd ^a   Wettstein, Philipp ^a   Stähelin, Christian ^a   Barbosa, Frédérique ^a   Neuburger, Markus ^a   Zehnder, Margareta ^a   Wessig, Pablo ^b  

^a UNIVERSITY OF BASEL   (Switzerland)

^b HUMBOLDT UNIVERSITY   (Germany)

Author keywords

Chirality; Memory effect; Photochemistry; Spinisomers

Indexed keywords

ALANINE DERIVATIVE; BENZOPHENONE; NAPHTHALENE DERIVATIVE;

ARTICLE; CHEMICAL BOND; CHIRALITY; CONFORMATIONAL TRANSITION; CYCLIZATION; ENERGY TRANSFER; ISOMER; PHOTOCHEMISTRY; RACEMIC MIXTURE; STEREOSPECIFICITY; STRUCTURE ACTIVITY RELATION; STRUCTURE ANALYSIS;

EID: 0033520303     PISSN: 14337851     EISSN: None     Source Type: Journal    
DOI: 10.1002/(SICI)1521-3773(19990903)38:17<2586::AID-ANIE2586>3.0.CO;2-K     Document Type: Article

References (25)

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6. See for instance: a) D. A. Plattner, Angew. Chem. 1999, 111, 86; Angew. Chem. Int. Ed. 1999, 38, 82; b) W. Adam, G. Fragale, D. Klapstein, W. M. Nau, J. Wirz, J. Am. Chem. Soc. 1995, 117, 12578.
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12. N2 substitution of ethyl O-trifluoromethanesulfonyl-L-lactate with methyl 4-tosylamino-2-siloxybutyrate followed by Dess-Martin periodinane oxidation. Its structure was elucidated by elemental analysis, NMR spectroscopy, and CD spectroscopy.
13. 2: about 2 h; naphthalene or isoprene: about 10 h). At 80-90% conversion the solutions were directly analyzed by analytical HPLC (column: Daicel Chiralcel OD, eluent: hexane/isopropyl alcohol, 3/1) to determine the yields (Table 1); yields refer to the conversions. Decreasing the irradiation times reduces the yields but has no effect on the product ratios. The four products were separated by preparative HPLC by using the same chiral column. The structural evidence is based on X-ray crystal structure analyses of derivatives of 3 and 4 in which the corresponding OH groups were esterified with (+)- and (-)-camphanic acid chloride, respectively. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC-116102 and CCDC-116103. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44) 1223-336-033; e-mail : deposit@ ccdc.cam.ac.uk).
14. 1-spinisomer are known: S. Davidson, D. Goodwin, P. Fornier de Violet, Tetrahedron Lett. 1981, 22, 2485.
15. 2 center in an enantioselective reaction. For a discussion on the memory effect in photochemical reactions, see: a) A. G. Griesbeck, H. Mauder, S. Stadtmüller, Acc. Chem. Res. 1994, 27, 70; b) J. C. Scaiano, Tetrahedron 1982, 38, 819.
16. 2 center in an enantioselective reaction. For a discussion on the memory effect in photochemical reactions, see: a) A. G. Griesbeck, H. Mauder, S. Stadtmüller, Acc. Chem. Res. 1994, 27, 70; b) J. C. Scaiano, Tetrahedron 1982, 38, 819.
17. 2 center in an enantioselective reaction. For a discussion on the memory effect in photochemical reactions, see: a) A. G. Griesbeck, H. Mauder, S. Stadtmüller, Acc. Chem. Res. 1994, 27, 70; b) J. C. Scaiano, Tetrahedron 1982, 38, 819.
18. Oxygen probably accelerates the triplet - singlet crossing of diradical 2. This diminishes the lifetime of the triplet state so strongly that the contribution coming from racemization of the helical triplet intermediate decreases: W. Adam, S. Grabowski, R. M. Wilson, Chem. Ber. 1989, 122, 561; R. D. Small, J. C. Scaiano, J. Am. Chem. Soc. 1978, 100, 4512.
19. Oxygen probably accelerates the triplet - singlet crossing of diradical 2. This diminishes the lifetime of the triplet state so strongly that the contribution coming from racemization of the helical triplet intermediate decreases: W. Adam, S. Grabowski, R. M. Wilson, Chem. Ber. 1989, 122, 561; R. D. Small, J. C. Scaiano, J. Am. Chem. Soc. 1978, 100, 4512.
20. 2) were determined following the actinometer method. It amounts to 0.07 ± 0.02 (trans-azobenzene as reference).
21. For the differences between excited singlet and triplet states in intermolecular H-abstractions, see: W. M. Nau, F. L. Cozens, J. C. Scaiano, J. Am. Chem. Soc. 1996, 118, 2275.
22. 1 state of naphthalene should be long enough for a diffusion- controlled energy transfer in a 1 M naphthalene solution.
23. The quantum chemical estimations were calculated following the "unrestricted Hartree-Fock" method with the 3-21G* basis set (Gaussian 94). The keyword "guess = mix" was used for the calculation of the singlet diradicals. Until now, DFT calculations of singlet diradical 2 did not lead to converging energies in our hands. For DFT calculations of singlet diradicals, see: E. R. Davidson, Int. J. Quant. Chem. 1998, 69, 241; J. Gräfenstein, E. Kraka, D. Cremer, Chem. Phys. Lett. 1998, 288, 593.
24. The quantum chemical estimations were calculated following the "unrestricted Hartree-Fock" method with the 3-21G* basis set (Gaussian 94). The keyword "guess = mix" was used for the calculation of the singlet diradicals. Until now, DFT calculations of singlet diradical 2 did not lead to converging energies in our hands. For DFT calculations of singlet diradicals, see: E. R. Davidson, Int. J. Quant. Chem. 1998, 69, 241; J. Gräfenstein, E. Kraka, D. Cremer, Chem. Phys. Lett. 1998, 288, 593.
25. The structure determination of 5 was performed by MS and 600 MHz NMR spectroscopy (two diastereomers in a ratio of about 1:1).