A Ni-catalyzed enantioselective
reductive diarylation of activated
alkenes by domino cyclizative/cross-coupling of two aryl bromides
is developed. This reaction proceeds under very mild conditions and
shows broad substrate scope, without requiring the use of preformed
organometallic reagents. Moreover, this approach provides direct access
to various bis-heterocycles bearing all-carbon quaternary centers
in synthetically useful yields (up to 81%) with excellent enantioselectivity
(>30 examples, 90–99% ee).
The first nickel-catalyzed domino Heck cyclization/Suzuki coupling reaction for the synthesis of 3,3-disubstituted oxindoles bearing quaternary all-carbon centers is reported. A wide range of electrophiles, such as aryl iodides, bromides, triflates, and chlorides, are all compatible with the reaction conditions. Moreover, cheap aryl esters, which undergo catalytic C-O bond cleavage, could also be employed as electrophiles. The approach shows good yields and broad scope, complementing a more practical and sustainable alternative to the conventional palladium-based analogues.
Transition-metal-catalytic domino
reactions represent important
advances in synthetic organic chemistry. Their development benefits
synthesis by providing highly efficient and step-economical methods
to complex molecules with impressive selectivity. Herein, a Ni-catalyzed
domino reductive cyclization of acrylamides with alkynyl bromides
is reported, enabling rapid assembly of a range of substituted 2,3-fused
cyclopentannulated indolines. Preliminary mechanistic studies revealed
that tricyclic indolines are afforded through a highly regioselective
migratory insertion of 1,3-diynes, which are formed from the homocoupling
of alkynyl bromides, into the in situ generated σ-alkyl-Ni(II)
species, followed by nucleophilic addition of the resulting alkenyl
nickel to unactivated amides. Most importantly, a highly regio- and
enantioselective reductive cyclization of acrylamides and internal
alkynes has also been developed. This transformation takes place under
mild conditions with high efficiency, providing a rapid access to
structurally diverse cyclopentannulated indolines in synthetically
useful yields with high regioselectivity (>20/1) and enantioselectivity
(27 examples, 82–96% ee).
A highly regioselective [2 + 2 + 2] cyclization of aromatic alkynes with nitriles is developed for the preparation of 2,3,6-trisubstituted pyridines under visible-light irradiation using a pyrylium salt as the photoredox catalyst. This cycloaddition is achieved through a photooxidative single-electron-transfer process at room temperature and under metal-free conditions. A variety of aromatic alkynes and nitriles are employed to furnish the annulation products in good yields.
Highly efficient (n)Bu3P-catalyzed desulfonylative [3 + 2] cycloadditions of allylic carbonates with arylazosulfones were developed for the synthesis of pyrazole derivatives. The reactions proceed smoothly under mild conditions to generate corresponding annulation products in good to excellent yields.
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