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Intramolecular Photoarylation of Alkenes by Phenyl Cations
Author(s) -
Dichiarante Valentina,
Fagi Maurizio,
Mella Mariella,
Albini Angelo
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200501392
Subject(s) - chemistry , methylene , deprotonation , acetonitrile , medicinal chemistry , adduct , ether , photochemistry , chloride , solvent , double bond , cyclohexane , organic chemistry , ion
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 arylCl 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.