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Synfacts 2010(8): 0872-0872  
DOI: 10.1055/s-0030-1257849
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart ˙ New York

Osmium-Catalyzed Synthesis of 3-Benzoxepines

Contributor(s): Victor Snieckus, Emilie David
A. Varela-Fernández, C. García-Yebra, J. A. Varela, M. A. Esteruelas*, C. Saá*
Universidad de Santiago de Compostela and Universidad de Zaragoza-CSIC, Spain
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Publication History

Publication Date:
22 July 2010 (online)

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Significance

Reported is the osmium-catalyzed synthesis of 3-benzoxepines by 7-endo-dig ­heterocyclization of terminal aromatic alkynols. Whereas rhodium, tungsten, and ruthenium ­catalysts give no or low conversions, the [CpOs(py)3]PF6 complex in pyridine afforded 3-benzoxepines in short reaction times and moderate yields. Primary, secondary, and tertiary alkynols are tolerated with faster reaction rates for electron-poor alkynols. Non-terminal alkynols failed to cyclize suggesting that the cyclization ­occurs via a catalytic metal vinylidene complex. A mechanism is proposed without evidence.

Book: J. Gonzalez, W. D. Harman, In Science of Synthesis, Vol. 1; M. Lautens, Ed.; Georg Thieme Verlag: Stuttgart, New York, 2001, 973-1076.

Review: C. Bruneau, P. H. Dixneuf Angew. Chem. Int. Ed. 2006, 45, 2176-2203.