The previously unexplored metal-catalyzed [5 + 2] cycloadditions of vinylcyclopropanes (VCPs) and electron-rich alkynes (ynol ethers) have been found to provide a highly efficient, direct route to dioxygenated seven-membered rings, a common feature of numerous natural and non-natural targets and building blocks for synthesis. The reactions proceed in high yield at room temperature and tolerate a broad range of functionalities. Substituted VCPs were found to react with high regioselectivity.
Ligand cross-linking is known to
improve the colloidal stability
of nanoparticles, particularly in aqueous solutions. However, most
cross-linking is performed chemically, in which it is difficult to
limit interparticle cross-linking, unless performed at low concentrations.
Photochemical cross-linking is a promising approach but usually requires
ultraviolet (UV) light to initiate. Using such high-energy photons
can be harmful to systems in which the ligand–nanoparticle
bond is fairly weak, as is the case for the commonly used semiconductor
quantum dots (QDs). Here, we introduce a novel approach to cross-link
thiolated ligands on QDs by utilizing the photocatalytic activity
of QDs upon absorbing visible light. We show that using visible light
leads to better ligand cross-linking by avoiding the problem of ligand
dissociation that occurs upon UV light exposure. Once cross-linked,
the ligands significantly enhance the colloidal stability of those
same QDs that facilitated cross-linking.
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