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Benzyl Radicals from Toluene by Photosensitization with Naphthalene‐1,4‐dicarbonitrile – Benzylation and Hydroxymethylation of Unsaturated Compounds
Author(s) -
Mella Mariella,
Fagi Maurizio,
Albini Angelo
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199909)1999:9<2137::aid-ejoc2137>3.0.co;2-r
Subject(s) - chemistry , radical , toluene , deprotonation , photochemistry , hydroxymethyl , electrophile , radical ion , electrophilic aromatic substitution , medicinal chemistry , organic chemistry , ion , catalysis
In aprotic media, photoinduced electron transfer from toluene to 1,4‐naphthalenedicarbonitrile (DCN) is followed by in‐cage proton transfer and radical coupling. However, in the presence of a protic co‐solvent, the radical ions diffuse out of the cage and deprotonation of the toluene radical cation takes place from the free solvated species. With t BuOH, this results in reductive benzylation of DCN through coupling of benzyl radicals with DCN – · . With MeOH, secondary hydrogen abstraction by PhCH 2 · yields hydroxymethyl radicals, which couple with DCN – · . Both benzyl and hydroxymethyl radicals are efficiently trapped by electrophilic alkenes. Thus, in the presence of dimethyl maleate, DCN‐photosensitized benzylation – or hydroxymethylation – of the substrate occurs through direct activation of the C–H bond. The same reaction has been accomplished with acrylonitrile, albeit with a lower yield.