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Volumn 48, Issue 27, 2007, Pages 4765-4770

Photoinduced electron transfer-initiated asymmetric cyclization of N-benzoyl-α-dehydronaphthylalanine alkyl esters carrying chiral and bulky auxiliaries

Author keywords

Amino acids and derivatives; Asymmetric induction; Dihydrooxazoles; Electron transfer; Photochemistry

Indexed keywords

DICHLOROETHANE; ESTER DERIVATIVE; METHANOL; N BENZYL ALPHA DEHYDRONAPHTHYLALANINE ALKYL ESTER DERIVATIVE; OXAZOLE DERIVATIVE; UNCLASSIFIED DRUG;

EID: 34249895026     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.tetlet.2007.04.134     Document Type: Article
Times cited : (8)

References (28)
  • 1
    • 0004167906 scopus 로고
    • Horspool W.M. (Ed), Plenum, New York
    • In: Horspool W.M. (Ed). Synthetic Organic Photochemistry (1984), Plenum, New York
    • (1984) Synthetic Organic Photochemistry
  • 2
    • 26644444613 scopus 로고    scopus 로고
    • Griesbeck A.G., and Mattay J. (Eds), Marcel Dekker, New York
    • In: Griesbeck A.G., and Mattay J. (Eds). Synthetic Organic Photochemistry (2005), Marcel Dekker, New York
    • (2005) Synthetic Organic Photochemistry
  • 13
    • 85050051598 scopus 로고    scopus 로고
    • Inoue Y., and Ramamurthy V. (Eds), Marcel Dekker, New York
    • In: Inoue Y., and Ramamurthy V. (Eds). Chiral Photochemistry (2004), Marcel Dekker, New York
    • (2004) Chiral Photochemistry
  • 24
    • 34249893735 scopus 로고    scopus 로고
    • 3: C, 77.19; H, 6.21; N, 3.75. Found: C, 77.18; H, 6.23; N, 3.46.
  • 25
    • 34249884587 scopus 로고    scopus 로고
    • note
    • 3: 373.1678. Found:373.1678.
  • 26
    • 34249875781 scopus 로고    scopus 로고
    • note
    • 3: C, 77.19; H, 6.21; N, 3.75. Found: C, 77.34; H, 6.25; N, 3.61.
  • 27
    • 34249872251 scopus 로고    scopus 로고
    • note
    • 2 = 0.0582. Crystallographic data of (4S,5S)-3 have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication number CCDC 636944. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44(0) 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).
  • 28
    • 34249892601 scopus 로고    scopus 로고
    • note
    • 8 The progress of π-face selective intramolecular addition within the (E)-1-derived radical anion (path A) is required for inducing asymmetry at the 5-position on the dihydrooxazole ring. This asymmetric addition results in a preferential formation of either the cyclized radical ion pair IIA or the IIB. There are two possible routes for back ET in the radical ion pair II. One is the transfer of unpaired electron from the 2-position on the oxazole ring to the amine radical cation, which gives a zwitterion intermediate. The other is the transfer of one of the paired electrons from the 4-position on the oxazole ring to the amine radical cation, as shown in Scheme 2. The electron-deficient carbon generated at the 2-position on the ring of the zwitterion is considered to greatly promote the dissociation of the N-H proton. If so, intramolecular proton shift in this intermediate is very unlikely to occur depending on the hydrogen-bonding ability of a given tertiary amine. Tertiary amine and temperature effects on the de for cis-2 and trans-2 in 1,2-dichloroethane favour the existence of the biradical intermediate III. While π-face selective intramolecular addition in (E)-I induces asymmetry at the 5-position on the oxazole ring of 2, asymmetric induction at the 4-position on this ring is accomplished by preferential hydrogen shift in either the re or the si face of III (Paths B and C in Scheme 2). The simultaneous C{double bond, long}N bond formation may provide a driving force for this hydrogen shift eventually leading to cis-2 and trans-2. The finding that hydrogen-boding interaction between III and tertiary amine is a major factor controlling de in 1,2-dichloroethane led us to propose hydrogen bond-assisted hydrogen shift in the re or the si face (Fig. 2).


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