Photoinduced decarboxylative benzylation of phthalimide triplets with phenyl acetates: a mechanistic study.
The photodecarboxylative benzylation of N-alkyl, N-arylalkyl, and N-aryl phthalimides with arylacetic acids in aqueous solution proceeds via electron transfer from the arylalkanoate to the excited triplet state of the phthalimide, either formed directly or upon sensitization with acetone. The rate constant for triplet quenching of N-methylphthalimide is k(q) < 10(7) M(-1) s(-1) for 2-phenylacetic acid and k(q) = (1-3) x 10(9) M(-1) s(-1) for its mono-, di- and trimethoxy-substituted derivatives, suggesting a change of the mechanism for the primary oxidation step from a Photo-Kolbe type reaction yielding an acyloxy radical to a pseudo-Photo-Kolbe process involving the formation of resonance-stabilized zwitterion radicals as intermediates.
Warzecha
Klaus-Dieter
KD
Institute of Organic Chemistry, University of Cologne, Greinstrasse 4, D-50939 Köln, Germany. klaus.warzecha@uni-koeln.de
Görner
Helmut
H
Griesbeck
Axel G
AG
D000838:Anions / Q000737:chemistry; D001554:Benzene / Q000737:chemistry*; D004579:Electron Transport; D004735:Energy Transfer; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010648:Phenylacetates / Q000737:chemistry*; D010777:Photochemistry; D010797:Phthalimides / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry
D000838:Anions; D010648:Phenylacetates; D010797:Phthalimides; D014867:Water; C037431:phthalimide; C025136:phenylacetic acid; D001554:Benzene