Radical cyclization by Ipso substitution of the methoxy group: Considerable effect of HMPA on samarium-mediated cyclization

Journal of Organic Chemistry

Volumn 68, Issue 15, 2003, Pages 5909-5916

  Ohno, Hiroaki ^a   Wakayama, Ryutaro ^a   Maeda, Shin ichiro ^a   Iwasaki, Hiroki ^a   Okumura, Mitsuaki ^a   Iwata, Chuzo ^a   Mikamiyama, Hidenori ^a   Tanaka, Tetsuaki ^a  

^a OSAKA UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

RADICAL CYCLIZATION;

CHELATION; CONFORMATIONS; SOLVENTS; SUBSTITUTION REACTIONS;

SAMARIUM COMPOUNDS;

ALKYL GROUP; CARBAMIC ACID DERIVATIVE; HEMPA; PROPANOL; SAMARIUM; TRIMETHYLSILYL DERIVATIVE;

ARTICLE; CHELATION; CHEMICAL STRUCTURE; CONFORMATION; CYCLIZATION; REACTION ANALYSIS; SUBSTITUTION REACTION;

EID: 0038034795     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo0343174     Document Type: Article

References (88)

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63. For reviews on samarium(II) iodide chemistry see: (a) Kagan, H. B.; Namy, J. L. Tetrahedron 1986, 42, 6573-6614. (b) Molander, G. A. Chem. Rev. 1992, 92, 29-68. (c) Molander, G. A.; Harris, C. R. Chem. Rev. 1996, 96, 307-338. (d) Molander, G. A.; Harris, C. R. Tetrahedron 1998, 54, 3321-3354. (e) Krief, A.; Laval, A.-M. Chem. Rev. 1999, 99, 745-777. (f) Steel, P. G. J. Chem. Soc., Perkin Trans. 1 2001, 2727-2751.
64. For reviews on samarium(II) iodide chemistry see: (a) Kagan, H. B.; Namy, J. L. Tetrahedron 1986, 42, 6573-6614. (b) Molander, G. A. Chem. Rev. 1992, 92, 29-68. (c) Molander, G. A.; Harris, C. R. Chem. Rev. 1996, 96, 307-338. (d) Molander, G. A.; Harris, C. R. Tetrahedron 1998, 54, 3321-3354. (e) Krief, A.; Laval, A.-M. Chem. Rev. 1999, 99, 745-777. (f) Steel, P. G. J. Chem. Soc., Perkin Trans. 1 2001, 2727-2751.
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78. We cannot rule out another mechanism through reduction of the electron-deficient aromatic ring, expulsion of the methoxy group, and attack of the resulting arene radical 46 on the carbonyl group (see below). However, the mechanistic pathway shown in Scheme 4 better explains both the experimental result that no demetoxylative reduction products such as 47 was obtained and that the ketone 33 is completely inert to the samarium-mediated cyclization conditions (Table 3, entry 5).
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85. Treatment of the diastereomixture 41 with DBU in the presence of air yielded the corresponding aromatized compound 48.
86. 2 and HMPA in the presence of i-PrOH gave an inseparable mixture of the recovered starting material and an unidentified cyclized product.
87. In 2001, Fang and Kuo reported a similar radical cyclization onto an aryl group substituted by a formyl or an ester group to form rearomatized products instead of the 1,4-cyclohexadiene derivatives, see ref 19.
88. According to a brief MO calculation performed by SPARTAN (v 5.1.1) with the MM2 method and the PM3 Hamiltonian, the electron density of the carbon para to the ester group is estimated to be higher than that bearing the methoxy group in the LUMO of the intermediate E.