Photoinduced electron-transfer oxygenation of arylalkanes. Generation and oxygenation pathways of benzylic-type free radicals from the cation radical deprotonation

Visible light flavin photo-oxidation of methylbenzenes, styrenes and phenylacetic acids

“…Photocatalytic oxidation reaction of tolane 14 28 gave benzil 15 as sole oxidation product in 28% yield leaving 2% of starting tolane 14 (Scheme 4). When the oxidation of tolane 14 was done in 18 O labelled water (10.5% 18 O content), the isotope peak with m/z = 212.1 (benzil m/z = 210.1) was found in a relative abundance of a factor 5.8 higher compared to a sample obtained from non-labelled water as confirmed by EI-MS. This indicates that water is acting, Scheme 4 Photocatalytic oxidation of tolane 14.…”

“…Whether the oxygen availability or the rising partial pressure of CO 2 in the head space upon expelling of CO 2 from the substrate is the limiting factor cannot be concluded from the collected data. No incorporation of 18 O was observed when the reaction was done in 18 O labelled water (10.5% 18 O content). Deuteration of the solvents did not have any impact on the photooxidation.…”

“…This kind of oxidative degradation is known from triphenylmethane radicals derived from triphenylmethyl halides 17 or triphenylmethane. 18 It was proposed that the triphenylmethane radical cation that is formed after initial ET to excited flavin loses a proton to form a triphenylmethyl radical. This is quenched by oxygen to form a peroxy radical that collapses into benzophenone and phenol.…”

“…This is quenched by oxygen to form a peroxy radical that collapses into benzophenone and phenol. 18 To gain more data on possible intermediates formed during the flavin-mediated photo-oxidation of 3a, we followed the course of the UV-Vis absorption of RFT under aerobic, oxygen saturated and anaerobic conditions (see ESI †). Strong bleaching of the RFT 1 absorption in the visible region with elongated irradiation times was observed.…”

Photocatalytic benzylic C–H bond oxidation with a flavin scandium complex

“…S1 †). 10 Note that the oxidations of p-trifluorobenzyl alcohol and p-nitrobenzyl alcohol proceed selectively, but the reaction speed is slow, resulting in an incomplete conversion. The reaction is significantly accelerated by higher Sc 3+ concentrations (Fig.…”