Intramolecular photoarylation of alkenes by phenyl cations

Chemistry : a European Journal
Valentina DichiaranteAngelo Albini

Abstract

Acetone-sensitized irradiation of various o-chlorophenyl allyl ethers in polar solvents led to either (dihydro)benzofurans or chromanes. The reaction appeared to involve photoheterolysis of the aryl-Cl bond followed by phenyl cation addition onto the tethered double bond either in 5-exo or 6-endo modes. The adduct cation gave the end products by deprotonation; addition of chloride anion or of the solvent, depending on the structure; and the conditions used. Preference for the 5-exo mode increased in passing from medium polarity (methylene chloride, ethyl acetate) to high polarity solvents (aqueous acetonitrile, methanol, 2,2,2-trifluoroethanol), for which this was often the exclusive path. The same compounds underwent photohomolysis when irradiated in cyclohexane, and radical cyclization was one of the process occurring. Substitution of a methylene group for the ether oxygen atom made 6-endo cyclization by far the main path in a related o-chlorophenylbutene. Again, the selectivity was higher in polar protic solvents. The results are discussed in terms of in cage ion pair versus free phenyl cation reactions.

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Nov 13, 2004·Chemistry : a European Journal·Ilse ManetAngelo Albini

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Citations

Dec 8, 2009·Journal of the American Chemical Society·Arthur H Winter, Daniel E Falvey
Jan 7, 2009·The Journal of Organic Chemistry·Luca PretaliMauro Freccero
Jan 27, 2011·Journal of the American Chemical Society·Stephen G Newman, Mark Lautens
Aug 3, 2011·The Journal of Organic Chemistry·Rabih JahjahNorbert Hoffmann
Jun 10, 2014·Journal of the American Chemical Society·Alexander T BuckArthur H Winter
Jan 7, 2021·Organic Letters·Yuliang LiuShunsuke Chiba
Aug 17, 2006·Journal of the American Chemical Society·Stefano ProttiAngelo Albini

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