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ChemComm
COMMUNICATION
Journal Name
photocatalyst Mes-Acr-MeClO4 (PC) was excited to [Mes-Acr- We thank CSIR for funding (Project No. 02(0338)/18/EMR-II
DOI: 10.1039/D0CC02352C
MeClO4]* under the irradiation of visible light and the excited dated 24-04-2018). M. P., K. C. thank NISER and A.M. thanks
PC (PC*) helped to produce intermediate 7 (radical cation of CSIR for fellowships.
benzyl alcohol) from benzyl alcohol via a single electron transfer
(SET) process19 and itself reduced to PC˙ˉ (radical anion of the
Conflicts of interest
“There are no conflicts to declare”
photocatalyst). The intermediate
intermediate
after releasing H+. Following, the PC˙ˉ generated
the superoxide radical which oxidized the intermediate to the
7 possibly led to the radical
8
8
corresponding aryl aldehyde and PC was regenerated. In a
similar manner, thiophenol 2a is expected to produce thiyl
radical 10 (Figure 6a). In the second step (Figure 6b), thiyl radical
reacted with benzaldehyde to produce hemithioacetal
Notes and references
1.
2.
3.
4.
5.
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intermediate 11 with the help of thiophenol 2a 14a
hemithioacetal 11 led to ether benzylidene(phenyl)sulfenium
12 or oxonium intermediate 13 depending upon the
.
Following,
,
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Das, Green Chem., 2019, 21, 1916.
substitution at the para-position of benzyl alcohol (groups like -
OMe or -NMe2 favours the formation of 13). In the presence of
thiyl radical, intermediate 12 was further converted to 14 which
led to the product dithioacetal 3aa via one electron reduction
by PC˙ˉ. However, the intermediate 13 which is electronic rich,
was further transformed into cation radical 15 via hydrogen
atom transfer (HAT) from thiophenol 2a 20
obtained by SET from PC˙ˉ
. Following, 4ma was
.
6.
7.
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Figure 6. Plausible reaction mechanism.
In summary, we have developed an unprecedented strategy
towards the C-S bond formation reaction via two step oxidative
processes directly from benzyl alcohols under visible light
photocatalysis via C-O bond functionalization. The Stern-
Volmer quenching, light ON-OFF-ON and EPR experiments
helped to establish the importance of the photocatalyst and
role of aerial dioxygen during the course of the reaction.
Mechanistically we have proposed that the reaction proceeded
via SET process. Various benzyl alcohols and thiophenols were
compatible with the standard condition and this fact supports
that the methodology is highly efficient. Thus we foresee that
this two-step oxidative C-O bond functionalization reaction in a
single step would offer a new synthetic route in organic
transformations.
4 | J. Name., 2012, 00, 1-3
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