Green Chemistry
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Notes and references
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Scheme 3 Proposed mechanism.
(see Fig. S4†). Gratifyingly, the adduct of intermediate INT1
with TEMPO was confirmed by ESI-HRMS.
We postulated a plausible mechanism for this aminothio-
cyanation process. The reaction begins with the visible light-
induced SET oxidation of NH4SCN15 (Eox = 0.61 V vs. SCE in
CH3CN) by the excited state photocatalyst *fluorescein16
(Er*ed ¼ 0:78 V vs: SCE) generating the thiocyanate radical and
the reduced species fluorescein•−. The fluorescein•− could be
oxidized with dioxygen to provide a superoxide and regenerate
•
the photocatalyst. Then, the SCN radical abstracts a hydrogen
from 1a to produce a carbon-centered radical and thiocyanic
acid (HSCN).13 The obtained α-carbonyl radical INT1 was sub-
•
sequently trapped by other SCN or (SCN)2 to form coupling
intermediate INT2, which has a more electron-deficient carbo-
nyl group and can be easily attacked by nucleophilic NH3.
Finally, the elimination of water from the adduct of INT2 and
NH3 affords the desired product (Scheme 3).
Conclusions
In summary, we have developed a highly efficient metal-free
visible-light promoted aminothiocyanation of activated
ketones using air as the terminal oxidant to afford
(E)-3-amino-2-thiocyanato-α,β-unsaturated compounds. The
net reaction is very clean and water is the only byproduct when
NH4SCN is used as the source of SCN and NH2. The resulting
multi-substituted olefins can be used as direct precursors to
construct an array of important molecules.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We are grateful for financial support from the NSFC (No.
21572090) and the Fundamental Research Funds for the
Central Universities (lzujbky-2017-k05).
This journal is © The Royal Society of Chemistry 2018
Green Chem., 2018, 20, 5464–5468 | 5467