TY - JOUR
T1 - Photoinduced electron-transfer oxidation of olefins with molecular oxygen sensitized by tetrasubstituted dimethoxybenzenes
T2 - A non-singlet-oxygen mechanism
AU - Mori, Tadashi
AU - Takamoto, Makolo
AU - Wada, Takehiko
AU - Inoue, Yoshihisa
PY - 2001/11/12
Y1 - 2001/11/12
N2 - α-Methylstyrene (1) was photo-oxidized in the presence of a series of alkylated dimethoxybenzenes as sensitizers in an oxygen-saturated MeCN solution to afford the cleaved ketone 2, epoxide 3, as well as a small amount of the ene product 4 in ca. 1:1:0.04 ratio. The relative rate of conversion was well-correlated with the fluorescence quantum yield of sensitizers. Thus, a non-singlet-oxygen mechanism is proposed, in which an excited sensitizer is quenched by (ground-state) molecular oxygen to produce a sensitizer radical cation and a superoxide ion (O2-·), the former of which oxidizes the substrate, while the latter reacts with the resulting olefin radical cation (1-·) to give the major oxidation products. Photodurability of such electron-donating sensitizers is dramatically improved by substituting four aromatic H-atoms in 1,4-dimethoxybenzene with Me or fused alkyl groups, which provides us with an environmentally friendly, clean method of photochemical functionalization with molecular oxygen, alternative to the ene reaction via singlet oxygenation.
AB - α-Methylstyrene (1) was photo-oxidized in the presence of a series of alkylated dimethoxybenzenes as sensitizers in an oxygen-saturated MeCN solution to afford the cleaved ketone 2, epoxide 3, as well as a small amount of the ene product 4 in ca. 1:1:0.04 ratio. The relative rate of conversion was well-correlated with the fluorescence quantum yield of sensitizers. Thus, a non-singlet-oxygen mechanism is proposed, in which an excited sensitizer is quenched by (ground-state) molecular oxygen to produce a sensitizer radical cation and a superoxide ion (O2-·), the former of which oxidizes the substrate, while the latter reacts with the resulting olefin radical cation (1-·) to give the major oxidation products. Photodurability of such electron-donating sensitizers is dramatically improved by substituting four aromatic H-atoms in 1,4-dimethoxybenzene with Me or fused alkyl groups, which provides us with an environmentally friendly, clean method of photochemical functionalization with molecular oxygen, alternative to the ene reaction via singlet oxygenation.
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U2 - 10.1002/1522-2675(20010919)84:9<2693::AID-HLCA2693>3.0.CO;2-3
DO - 10.1002/1522-2675(20010919)84:9<2693::AID-HLCA2693>3.0.CO;2-3
M3 - Article
AN - SCOPUS:0034760858
VL - 84
SP - 2693
EP - 2707
JO - Helvetica Chimica Acta
JF - Helvetica Chimica Acta
SN - 0018-019X
IS - 9
ER -