Brønsted Acid-Catalyzed Enantioselective Synthesis of Isatin- DerivedN,S-Acetals

Enantioselective Friedel-Crafts Reaction for the Synthesis of 4,7-Difunctionalized Indoles Featuring a Chiral Heteroatom-Substituted Quaternary Carbon at the C7 Position

Enantioselective functionalization of 4-aminoindoles at the site-specific C7 position via a chiral phosphoric acid-catalyzed Friedel-Crafts reaction with cyclic thioimidates was developed. This approach enables the formation of 4,7-difunctionalized indoles incorporating the chiral N,S-acetal motif with excellent yield and enantioselectivity (up to 99% yield and >99% ee). The protocol is also compatible with isatin-derived ketoimines for the highly enantioselective synthesis of 4,7-difunctionalized indole derivatives bearing aza-quaternary carbon at the C7 position. The synthetic potential was demonstrated by gram-scale experiments and versatile transformations of the products, with the method characterized by low catalyst loading, site specificity, excellent enantioselectivity, and a broad substrate scope.

Copper(II)-Catalyzed Enantioselective Addition of Aryl Amines to Isatin-Derived N-Boc-Ketimines for the Synthesis of Acyclic N,N'-Ketals

Here, we demonstrated a copper(II)-catalyzed enantioselective addition of aryl amines to isatin-derived N-Boc-ketimines using chiral O-N-N tridentate ligands derived from BINOL and proline. Generally, the chiral acyclic N,N'-ketals were obtained in high yields (up to 98%) and excellent ee values (up to 98%). Various aryl amines could be tolerated and a gram-scale reaction was also possible. Further, an X-ray diffraction experiment confirmed that the configuration of isatin-derived N-Boc ketimine should be (Z). Confirmation of the configuration of the ketimine would make it easier to understand the rationale for stereofacial selective activation of the electrophile with either organo- or Lewis acid-based catalysts.

Organocatalytic enantioselective aza-Friedel–Crafts alkylation of β-naphthols and isatin-derived ketimines via a Takemoto-type catalyst

The catalyst type and the substrate scope were broadened using this methodology.

Enantioselective synthesis of chiral α-alkynylated thiazolidones by tandem S-addition/acetalization of alkynyl imines

A SPINOL-derived chiral phosphoric acid catalyzed asymmetric formal [2 + 3]-annulation of in situ generated alkynyl imines and 1,4-dithiane-2,5-diol has been developed to afford enantiopure α-alkynylated thiazolidones with up to 72% yield and 98.5 : 1.5 er. This tandem annulation involved a tandem S-addition of alkynyl imines/intramolecular acetalization, followed by PDC-mediated oxidation. The α-alkynylated thiazolidones could facilely afford the corresponding chiral α-alkynylated or α-alkenylated cyclic sulfoxides via further elaboration.

Bifunctional thiourea-modified polymers of intrinsic microporosity for enantioselective α-amination of 3-aryl-2-oxindoles in batch and flow conditions

A multigram scale preparation of enantioenriched 3-aryl-3-amino-2-oxindoles promoted by a novel chiral bifunctional thiourea, readily prepared from polymers of intrinsic microporosity.

Enantioselective addition of thiols to trifluoromethyl ketimines: synthesis of N,S-ketals

Enantioselective addition of thiols to acyclic trifluoromethyl ketimines for the construction of trifluoromethylated N,S-ketals was performed successfully using a bifunctional squaramide catalyst.

Enantioselective Reaction of 2H-Azirines

2H-Azirines are useful precursors for the synthesis of a variety of chiral aziridine and amine derivatives with a range of biological activities. Owing to the ring strain and the presence of a C=N double bond, 2H-azirines are more reactive than other types of ketimine, and undergo a range of enantioselective reactions, including reduction and Diels-Alder reactions, as well as nucleophilic addition to the C=N double bond. Therefore, the enantioselective reactions of 2H-azirines has become a hot topic, in particular within the last few years. In this Minireview, we focus on the enantioselective reactions of 2H-azirines by using catalytic or stoichiometric amounts of chiral additives, the reaction mechanisms, and the applications of these reactions of 2H-azirines and related compounds in organic synthesis.

N-Sulfonyl Bisimidazoline Ligands and Their Applications in Pd(II)-Catalyzed Asymmetric Addition toward α-Tertiary Amines

A new class of chiral N-sulfonyl bisimidazoline (Bim) ligands have been designed, prepared, and applied in Pd(II)-catalyzed asymmetric addition of arylboronic acids to isatin-derived N-Boc ketimines. The combination of Pd(OCOCF₃)₂ and N-tosyl Bim ligand shows high catalytic activity and excellent asymmetric induction, enabling asymmetric addition to offer α-tertiary amines with generally good to high yields and excellent enantioselectivity (up to 96% yield, 96% ee). This asymmetric Pd(II) catalysis can tolerate air conditions, providing a practical and operationally simple protocol toward the construction of an enantioenriched α-tertiary stereocenter.

A copper(i)-catalyzed asymmetric Mannich reaction of glycine Schiff bases with isatin-derived ketimines: enantioselective synthesis of 3-substituted 3-aminooxindoles

We have developed a copper/Ph-Phosferrox-catalyzed asymmetric Mannich reaction of Schiff bases with isatin-derived ketimines to prepare 3-substituted 3-aminooxindoles with excellent results.

Lipase catalyzed 1,2-addition of thiols to imines under mild conditions

PPL, chymosin and BSA as efficient biocatalysts (low catalyst loading, high yields) in an eco-friendly synthesis of N,S-acetals.

Organocatalytic enantioselective Mannich-type addition of 5H-thiazol-4-ones to isatin-derived imines: access to 3-substituted 3-amino-2-oxindoles featured by vicinal sulfur-containing tetrasubstituted stereocenters

3-Substituted 3-amino-2-oxindoles featuring both 5H-thiazol-4-one and vicinal sulfur-containing tetrasubstituted stereocenter structural motifs were obtained in high yields with excellent enantioselectivities and diastereoselectivities.

Enantioselective Synthesis of N,S-Acetals by an Oxidative Pummerer-Type Transformation using Phase-Transfer Catalysis

Reported is the first enantioselective oxidative Pummerer-type transformation using phase-transfer catalysis to deliver enantioenriched sulfur-bearing heterocycles. This reaction includes the direct oxidation of sulfides to a thionium intermediate, followed by an asymmetric intramolecular nucleophilic addition to form chiral cyclic N,S-acetals with moderate to high enantioselectivites. Deuterium-labelling experiments were performed to identify the stereodiscrimination step of this process. Further analysis of the reaction transition states, by means of multidimensional correlations and DFT calculations, highlight the existence of a set of weak noncovalent interactions between the catalyst and substrate that govern the enantioselectivity of the reaction.

Catalytic asymmetric synthesis of hetero-substituted oxindoles

The construction of chiral disubstituted oxindoles is an intriguing challenge for organic chemists.

Effective asymmetric vinylogous Mannich reaction of isatin imines with α,α-dicyanoolefins in the presence of a simple chiral amide phosphonium bifunctional phase transfer catalyst

A Mannich reaction between N-Boc isatin imine and α,α-dicyanoolefin as well as subsequent oxidative cleavage of the malonic nitrile moiety were described.

Asymmetric Mannich reaction: highly enantioselective synthesis of 3-amino-oxindoles via chiral squaramide based H-bond donor catalysis

A facile formation of 3-aminooxindole derivatives from the reaction of 1,3-diketones with isatin (N-Boc) via an asymmetric Mannich reaction catalyzed by chiral cinchona alkaloid based squaramide containing H-bond donor catalysts.

Imidazolylpyridine-In(OTf)3 catalyzed enantioselective allylation of ketimines derived from isatins

An enantioselective In(OTf)₃-catalyzed allylation of ketimines derived from isatins in the presence of an imidazolylpyridine ligand is described.

Chiral Brønsted acid-catalysed enantioselective synthesis of isoindolinone-derived N(acyl),S-acetals

Chiral Brønsted acid catalyzed synthesis of N(acyl),S-acetals from in situ generated ketimines proceeds in high yields and enantioselectivities.

Asymmetric additions of thioglycolates and N-Boc aldimines catalyzed by a bifunctional tertiary-amine squaramide

A highly enantioselective asymmetric addition reaction of thioglycolates and N-Boc aldimines was promoted by a bifunctional tertiary-amine squaramide catalyst.

Asymmetric synthesis of 3,3′-pyrrolidinyl-dispirooxindoles via a one-pot organocatalytic Mannich/deprotection/aza-Michael sequence

A highly stereoselective synthesis of functionalized 3,3′-pyrrolidinyl-dispirooxindole derivatives with three stereogenic centers, including two contiguous spiro-stereocenters, has been achieved through an organocatalytic Mannich/Boc-deprotection/aza-Michael sequence.

A highly efficient Mukaiyama–Mannich reaction of N-Boc isatin ketimines and other active cyclic ketimines using difluoroenol silyl ethers catalyzed by Ph3PAuOTf

A Ph₃PAuOTf catalyzed highly efficient reaction of difluoroenoxysilanes and active ketimines is reported, which represents the first Au(i)-catalyzed Mukaiyama–Mannich reaction.

Stereoselective synthesis of 3-amino-2-oxindoles from isatin imines: new scaffolds for bioactivity evaluation

3-Substituted-3-aminooxindole motifs constitute the core structure of a number of natural products and drug candidates.