Enantioselective β-Protonation of Enals via a Shuttling Strategy

Sulfinate and Carbene Co-catalyzed Rauhut-Currier Reaction for Enantioselective Access to Azepino[1,2-a]indoles

A carbene and sulfinate co-catalyzed intermolecular Rauhut-Currier reaction between enals and nitrovinyl indoles is disclosed. The carbene catalyst activates the enal and the sulfinate co-catalyst activates the nitrovinyl indole. Both activation processes are realized via the formation of covalent bonds between the catalysts and substrates to generate catalyst-bound intermediates. The dual catalytic reaction affords azepino[1,2-a]indole products with excellent stereoselectivity. Our study demonstrates the unique involvement of sulfinate as an effective nucleophilic catalyst in activating electron-deficient alkenes for asymmetric reactions. This dual catalytic approach should also encourage future explorations of both sulfinate and carbene catalysts for new reactions.

Enantioselective Hydroamidation of Enals by Trapping of a Transient Acyl Species

An enantioselective synthesis of β-chiral amides through asymmetric and redox-neutral hydroamidation of enals is reported. In this reaction, a chiral N-heterocyclic carbene (NHC) catalyst reacts with enals to generate the homoenolate intermediate. Upon highly enantioselective β-protonation through proton-shuttle catalysis, the resulting azolium intermediate reacts with imidazole to yield the key β-chiral acyl species. This transient intermediate provides access to diversified β-chiral carbonyl derivatives, such as amides, hydrazides, acids, esters, and thioesters. In particular, β-chiral amides can be prepared in excellent yield and ee (40 chiral amides, up to 95 % yield and 99 % ee). This modular strategy overcomes the challenge of disruption of the highly selective proton-shuttling process by basic amines.

Asymmetric synthesis of γ-branched amines via rhodium-catalyzed reductive amination

Amines bearing γ-stereocenters are highly important structural motifs in many biologically active compounds. However, reported enantioselective syntheses of these molecules are indirect and often require multiple steps. Herein, we report a general asymmetric route for the one-pot synthesis of chiral γ-branched amines through the highly enantioselective isomerization of allylamines, followed by enamine exchange and subsequent chemoselective reduction. This protocol is suitable for establishing various tertiary stereocenters, including those containing dialkyl, diaryl, cyclic, trifluoromethyl, difluoromethyl, and silyl substituents, which allows for a rapid and modular synthesis of many chiral γ-branched amines. To demonstrate the synthetic utility, Terikalant and Tolterodine are synthesized using this method with high levels of enantioselectivity.

Biologically active compounds often contain a chiral centre in proximity of amine groups. Here, the authors developed a strategy involving asymmetric isomerization of allylic amines, enamine exchange and chemoselective reduction for the one-pot highly enantioselective synthesis of gamma-branched amines.

Enantioselective cooperative proton-transfer catalysis using chiral ammonium phosphates

Chiral phosphorate anions are shown to be highly enantioselective templates for proton-transfer catalysis.

N-Heterocyclic carbene-catalyzed sulfa-Michael addition of enals

An efficient N-heterocyclic carbene (NHC) catalyzed sulfa-Michael addition (SMA) between enals and thiols has been developed.