Intramolecular [4 + 2] cycloadditions of benzynes with conjugated enynes, arenynes, and dienes

Organic Letters

Volumn 7, Issue 18, 2005, Pages 3917-3920

  Hayes, Martin E ^a   Shinokubo, Hiroshi ^a   Danheiser, Rick L ^a  

^a MASSACHUSETTS INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 24944521269     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol051372l     Document Type: Article

References (33)

1. For recent examples of thermal and Lewis-acid-promoted enyne and "heteroenyne" cycloadditions, see: (a) Danheiser, R. L.; Gould, A. E.; Fernandez de la Pradilla, R.; Helgason, A. L. J. Org. Chem. 1994, 59, 5514.
2. (b) Wills, M. S. B.; Danheiser, R. L. J. Am. Chem. Soc. 1998, 120, 9378.
3. (c) Dunetz, J. R.; Danheiser, R. L. J. Am. Chem. Soc. 2005, 127, 5776 and references therein.
4. Early examples of enyne and arenyne cycloadditions are reviewed in: Onishchenko, A. S. Diene Synthesis; Israel Program for Scientific Translations: Jerusalem, 1964; pp 249-254 and 635-637.
5. For reviews of transition-metal-catalyzed enyne cycloadditions, see: (a) Rubin, M.; Sromek, A. W.; Gevorgyan, V. Synlett 2003, 2265.
6. (b) Saito, S.; Yamamoto, Y. Chem. Rev. 2000, 100, 2901.
7. For recent examples of cycloadditions of conjugated arenynes (the "Michael-Bucher reaction"), see: (a) Rodríguez, D.; Martínez-Esperón, M. F.; Navarro-Vázquez, A.; Castedo, L.; Domínguez, D.; Saá, C. J. Org. Chem. 2004, 69, 3842.
8. (b) Martínez-Esperón, M. F.; Rodríguez, D.; Castedo, L.; Saá, C. Org. Lett. 2005, 7, 2213 and references therein.
9. Reviews: (a) Hoffmann, R. W. Dehydrobenzene and Cycloalkynes; Academic Press: New York, 1967.
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13. Transformation 1→2 may proceed via a concerted cycloaddition or may involve a stepwise mechanism involving an intermediate biradical. For a discussion of stepwise mechanisms in benzyne cycloadditions, see ref 5. For a discussion of biradical intermediates in arenyne cycloadditions, see: Rodríguez, D.; Navarro, A.; Castedo, L.; Domínguez, D.; Saá, C. Org. Lett. 2000, 2, 1497.
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23. (b) For an earlier report on the generation of benzynes by fluoride-promoted elimination of o-(tnmethylsilyl)aryl chlorides, see: Cunico, R. F.; Dexhemier, E. M. J. Organomet. Chem. 1973, 59, 153.
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27. Interestingly, Kobayashi reports that none of the expected cycloadduct with furan was obtained when benzyne generation was attempted using KF under similar conditions (ref 10a).
28. Pilcher, A. S.; DeShong, P. J. Org. Chem. 1996, 61, 6901.
29. Cycloadduct 9 was obtained in 54% yield when 1.5 equiv of TBAT and 0.5 equiv of BHT were employed.
30. Under the same conditions but in the absence of BHT, the cycloadduct 9 is obtained in only 27% yield. We believe that BHT serves as a hydrogen and/or proton donor in facilitating the isomerization of cyclic allene intermediates of type 2 to the aromatic products.
31. We speculate that substitution at this position suppresses side reactions of the intermediate cyclic allene 2, possibly including intermolecular trapping by benzyne intermediates.
32. (a) Connon, S. J.; Blechert, S. Angew. Chem., Int. Ed. 2003, 42, 1900.
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