The complexity of heterogeneous metal
catalysts makes it challenging
to gain insights into their catalytic mechanisms. Thus, there exists
a huge gap between heterogeneous catalysis and organometallic catalysis.
With the success in the preparation of highly robust atomically precise
metal nanocluster catalysts (i.e., [Au16(NHC-1)5(PA)3Br2]3+ and [Au17(NHC-1)4(PA)4Br4]+, where
NHC-1 is a bidentate NHC ligand, and PA is phenylacetylide) with surface
organometallic motifs anchored on the metallic core, we demonstrate
in this work how the metallic core works synergistically with the
surface organometallic motifs to enhance the catalysis. More importantly,
the discovery allows the development of highly stable and recyclable
heterogeneous metal catalysts to achieve efficient hydroamination
of alkynes with an extremely low catalyst dosage (0.002 mol %), helping
bridge the gap between heterogeneous and homogeneous metal catalysis.
The surface modification of metal nanocatalysts with organometallic
motifs provides a new design principle of metal catalysts with enhanced
catalysis.
In the past decades,
significant advances have been made on radical
Smiles rearrangement. However, the eventually formed radical intermediates
in these reactions are limited to the amidyl radical, except for the
few examples initiated by a N-centered radical. Here, a novel and
practical radical Smiles rearrangement triggered by photoredox-catalyzed
regioselective ketyl–ynamide coupling is reported, which represents
the first radical Smiles rearrangement of ynamides. This method enables
facile access to a variety of valuable 2-benzhydrylindoles with broad
substrate scope in generally good yields under mild reaction conditions.
In addition, this chemistry can also be extended to the divergent
synthesis of versatile 3-benzhydrylisoquinolines through a similar
ketyl–ynamide coupling and radical Smiles rearrangement, followed
by dehydrogenative oxidation. Moreover, such an ynamide Smiles rearrangement
initiated by intermolecular photoredox catalysis via addition of external
radical sources is also achieved. By control experiments, the reaction
was shown to proceed via key ketyl radical and α-imino carbon
radical intermediates.
This review summarizes the latest trends and developments of Brønsted acid-mediated reactions of ynamides, including cycloaddition, cyclization and so on.
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