Light driven excitation
of gold nanoparticles (GNPs) has emerged
as a potential strategy to generate hot carriers for photocatalysis
through excitation of localized surface plasmon resonance (LSPR).
In contrast, carrier generation through excitation of interband transitions
remains a less explored and underestimated pathway for photocatalytic
activity. Photoinduced oxidative etching of GNPs with FeCl3 was investigated as a model reaction in order to elucidate the effects
of both types of transitions. The quantitative results show that interband
transitions more efficiently generate hot carriers and that those
carriers exhibit higher reactivity as compared to those generated
solely by LSPR. Further, leveraging the strong π-acidic character
of the resulting photogenerated Au+ hole, an interband
transition induced cyclization reaction of alkynylphenols was developed.
Notably, alkyne coordination to the Au+ hole intercepts
the classic oxidation event and leads to the formation of the catalytically
active gold clusters on subnanometer scale.
C(sp)-H bond functionalization has emerged as a robust tool enabling rapid construction of molecular complexity from simple building blocks, and the development of asymmetric versions of this reaction creates a powerful methodology to access enantiopure sp-rich materials. Herein, we report the stereoselective functionalization of C(sp)-H bonds of cyclic ethers employing a photochemically active diaryliodonium salt in combination with an anionic phase-transfer catalyst. The synthetic strategy outlined herein allows for regio- and stereochemical control in the α-C-H acetalization of furans and pyrans using alcohol nucleophiles, thus providing the ability to control the configuration at the stereogenic exocyclic acetal carbon.
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