Reported here is a novel photoinduced strategy for the
borylation of aryl sulfonium salts using bis(pinacolato)diboron as
the boron source. This method exploits redox-neutral aryl sulfoniums
to gain access to aryl radicals via C–S bond activation upon
photoexcitation under transition-metal-free conditions. Therefore,
it grants access to diverse arylboronate esters with good performance
from easily available aryl sulfoniums accompanied by mild conditions,
operational simplicity, and easy scalability.
The
synergistic combination of N-heterocyclic
carbene organocatalysis and transition-metal catalysis for a formal
[3 + 2] annulation between 3-substituted but-2-enoates and 1-tosyl-2-vinylaziridine
was developed. This cooperative strategy provides a facile and efficient
access to various functionalized (E)-3-ethylidene-4-vinylpyrrolidin-2-ones
in a regioselective and stereoselective manner. The preliminary asymmetric
studies were also performed, which indicated a potential for enantioselective
annulation of vinyl enolate intermediates with transition-metal−π-allyl
species.
The structurally interesting pyrano[3,2-b]indol-2-ones were synthesized by an N-heterocyclic carbene-catalyzed formal [3 + 3] annulation of alkynoic acid esters.
An N-heterocyclic
carbene (NHC)-catalyzed formal [4 + 2] annulation of 2-aryl-3H-indol-3-ones with α,β-unsaturated carboxylic
acids bearing γ-H was developed via an in situ activation strategy.
The reaction involves the γ-addition of vinyl enolates to the
unique cyclic ketimines to afford chiral tricyclic indolin-3-ones
with a quaternary carbon center at 2-position. This protocol provides
a rapid and enantioselective pathway to access a novel class of structurally
important C2-quaternary indolin-3-ones that might be useful for drug
discovery.
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