Classic nucleophilic substitution reactions (SN1 and SN2) are not generally amenable to the enantioselective variants that use simple and racemic alkyl halide electrophiles. The merging of transition metal catalysis and radical chemistry with organometallic nucleophiles is a versatile method for addressing this limitation. Here, we report that visible light-driven catalytic asymmetric photoredox radical coupling can act as a complementary and generic strategy for the enantioconvergent formal substitution of alkyl haldies with readily available and bench-stable organic molecules. Single-electron reductive debrominations of racemic α-bromoketones generate achiral alkyl radicals that can participate in asymmetric Csp3–Csp3 bonds forming cross-coupling reactions with α-amino radicals derived from N-aryl amino acids. A wide range of valuable enantiomerically pure β2- and β2,2-amino ketones were obtained in satisfactory yields with good-to-excellent enantioselectivities by using chiral phosphoric acid catalysts to control the stereochemistry and chemoselectivity. Fluoro-hetero-quaternary and full-carbon quaternary stereocenters that are challenging to prepare were successfully constructed.
A novel enantioselective protonation
protocol that is triggered
by reductive cross coupling of olefins is reported. When under cooperative
photoredox and chiral hydrogen-bonding catalytic conditions and using
a terminal reductant, various α-branched vinylketones with diverse
vinylazaarenes could provide important enantioenriched azaarene derivatives
containing tertiary stereocenters at their remote δ-position
with high yields and enantioselectivities. This reaction system is
also suitable for α-branched vinylazaarenes, thus successfully
assembling elusive 1,4-stereocenters. The convenient late-stage modifications
of products, especially the formation of remote ε-tertiary and
ε-heteroquaternary carbon stereocenters, further highlight the
important synthetic value of this method. Control experiments and
density functional theory (DFT) calculations were conducted to elucidate
the plausible reaction mechanism and origins of regioselectivity and
stereoselectivity.
A series of dicyanopyrazine and dicyanoimidazole derived push‐pull molecules have been prepared and further investigated as photoredox catalysts. The fundamental properties of the catalysts were studied by DSC, X‐ray analysis, absorption/emission spectra, and electrochemistry and were completed with the DFT results. The catalytic activity has been evaluated in visible light induced α‐functionalization of amines (cross‐dehydrogenative coupling and annulation reaction of tetrahydroisoquinolines). Thorough structure‐property‐catalytic activity relationships were elucidated. The developed series of tailored organic photoredox catalysts allows synthetic chemists to perform desired reactions under sustainable and mild conditions employing solely visible light as a source of energy.
Herein, the intermolecular hydroamination of alkenes and alkynes with anilines catalyzed by HOTf under mild conditions has been developed.This reaction provides one of the simplest alkene and alkyne addition methods and is an alternative to metal-catalyzed reactions. At the same time, the intramolecular hydroamination of alkynes with anilines proceeds smoothly to obtain quinolines. We found that this strategy is efficient in building complex structures from simple starting materials in an environmentally benign fashion.
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