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By oxidation of CeCl3 with O2, a cerium(IV) species could be Notes and references
generated. It is assumed that in the presence of TBACl, the
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catalytically active complex (n-Bu4N)2Ce(IV)Cl6 is formed.13a Upon
deprotonation of the diol, presumably only one of the hydroxy
groups coordinates to the cerium(IV) catalyst.14 This complex absorbs
blue light (455 nm), which triggers homolytic bond cleavage of the
O–Ce bond. On the one side, this regenerates the cerium(III) catalyst.
On the other side, an alkoxy radical is formed which is believed
to undergo b-scission to an aldehyde and an a-hydroxy radical.
Hydrogen atom transfer (HAT) from this a-hydroxy radical to the
solvent or another alkoxy radical would give the second aldehyde. In
summary, we have developed a cerium-catalysed, light-mediated
method for the cleavage of vicinal diols to aldehydes or ketones.
The protocol is equally well applicable for benzylic and aliphatic
diols and gives the aldehyde cleavage products in good to very good
yields. Moreover, the reaction works under air, is easy to perform
and does not require expensive or toxic additives. With further
investigations and optimization, we want to extend the scope to
natural and abundant polyols like sugars in order to make this class
of compounds accessible for selective C–C bond cleavage.
2 R. Criegee, Ber. Dtsch. Chem. Ges. B, 1931, 64, 260–266.
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We thank the German Science Foundation (DFG) (GRK 1626,
Chemical Photocatalysis) for financial support and J. S. thanks
the Deutsche Bundesstiftung Umwelt (DBU) for a graduate
scholarship.
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Conflicts of interest
There are no conflicts to declare.
488 | Chem. Commun., 2019, 55, 486--488
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