Catalytic Asymmetric Construction of Vicinal Tetrasubstituted Stereocenters by the Mannich Reaction of Linear α-Substituted Monothiomalonates with Isatin N-Boc Ketimines

Cinchona Organocatalyzed Enantioselective Amination for Quaternized Serines as Tertiary Amides

Herein, we describe a Cinchona-aminocatalyzed enantioselective α-hydrazination of an α-formyl amide for the production of protected quaternized serines as tertiary amides with ee's of generally >98% and ≤99% yields. The proposed TS model supported by density functional theory calculations involves a quinuclidinium ion Brønsted acid-assisted delivery of DtBAD, which occurs from the Re face of an H-bonded enaminone when using a 9S-cinchonamine catalyst, resulting in a hydrazide with the R-configuration as determined by X-ray analysis.

Organocatalyzed Enantioselective Aza-Morita-Baylis-Hillman Reaction of Cyclic Ketimine with α,β-Unsaturated γ-Butyrolactam

The enantioselective aza-MBH reaction is an efficient strategy for constructing novel carbon-carbon bonds, providing access to multitudinous chiral densely functionalized MBH products. However, the enantioselective aza-MBH reaction of cyclic-ketimines that would generate a versatile synthon is still missing and challenging. Herein, we developed a challenging direct organocatalytic asymmetric aza-MBH reaction involving cyclic ketimines attached to a neutral functional group. Moreover, the α,β-unsaturated γ-butyrolactam was utilized as a rare nucleophile alkene in this work. The reactions provide enantiomerically enriched 2-alkenyl-2-phenyl-1,2-dihydro-3H-indol-3-ones, bearing with a tetra-substituted stereogenic center. Moreover, this reaction features high α-selectivities, high enantioselectivities (up to 99% ee), and good yields (up to 80%).

Enantioselective Reaction of 2H-Azirines with Oxazol-5-(4H)-ones Catalyzed by Cinchona Alkaloid Sulfonamide Catalysts

The enantioselective reaction of 2H-azirines with oxazol-5-(4H)-ones (oxazolones) using a cinchona alkaloid sulfonamide catalyst has been developed. The reaction proceeded at the C-2 position of oxazolones to afford products with consecutive tetrasubstituted stereogenic centers in high yield with high diastereo- and enantioselectivity. The obtained aziridines were converted into various chiral compounds without loss of enantiopurity.

Bifunctional squaramide catalyzed stereoselective Mannich reaction of α-azido ketones with isatin-derived ketimines

Bifunctional squaramide catalyzed asymmetric Mannich reaction of alpha-azido ketones and isatin derived ketiminines were established for the first time with high stereoselectivity. Adducts are valuable synthons for optically active heterocycles.

Cu(I)-Catalyzed Asymmetric Mannich Reaction of Glycine Schiff Bases to Ketimines

A copper-catalyzed asymmetric Mannich reaction between glycine Schiff bases and ketimines has been developed. This method afforded 2-oxindole-based chiral syn-α,β-diamino acid derivatives in high yields (89-99%) with good to excellent diastereoselectivities (≤98:2 dr) and excellent enantioselectivities (95-99% ee).

Enantioselective Mannich reaction between rhodanines and isatin-derived ketimines to construct vicinal tetrasubstituted stereocenters

An organocatalytic enantioselective Mannich reaction between rhodanines and isatin-derived ketimines was developed. With 2 mol% of a quinine-based tertiary amine-thiourea catalyst C2, 3,3-disubstituted oxindoles with vicinal tetrasubstituted stereocenters were obtained in moderate-to-excellent yields (43-99%) with excellent diastereoselectivities (98 : 2-99 : 1 dr) and good-to-excellent enantioselectivities (up to 97% ee). The readily available substrates, low catalyst loading and high stereoselectivity are the major features.

The enantioselective addition of 1-fluoro-1-nitro(phenylsulfonyl)methane to isatin-derived ketimines

An asymmetric organocatalytic addition of fluorinated phenylsulfonylnitromethane to isatin-derived ketimines was developed. The reaction was efficiently catalyzed by a chiral tertiary amine, cinchonine. This methodology provides a new type of optically active compound with two adjacent quaternary carbon stereocenters in good yield (up to 96%), with moderate diastereoselectivity (up to 5.7 : 1 dr) and excellent enantioselectivity (up to 98/96% ee).

Catalyst-Free 1,6-Conjugate Addition/Aromatization/Sulfonylation of para-Quinone Methides: Facile Access to Diarylmethyl Sulfones

An efficient, catalyst-free strategy to construct diarylmethyl sulfones via 1,6-conjugate addition/aromatization/sulfonylation reaction of para-quinone methides with sulfonyl hydrazides under mild and environmentally benign conditions has been developed. The established protocol provided a highly chemo- and regioselectivity synthesis of a diverse array of novel diarylmethyl sulfones with excellent yields, and the reaction could be scaled up.

Catalytic synthesis of 3-aminooxindoles via addition to isatin imine: an update

3-Substituted-3-aminooxindoles have attracted the attention of organic chemist to develop different synthetic methodologies for their synthesis using catalysts. This review covers the recent developments.

Direct Access to N-Unprotected α- and/or β-Tetrasubstituted Amino Acid Esters via Direct Catalytic Mannich-Type Reactions Using N-Unprotected Trifluoromethyl Ketimines

Direct catalytic C-C bond-forming addition to N-unprotected ketimines is an efficient and straightforward method of synthesizing N-unprotected tetrasubstituted amines that eliminates prior protection/deprotection steps and allows facile transformation of the products. Despite its advantages, however, N-unprotected ketimines have difficulties in C-C bond-forming reactions, and only a limited number of reactions and substrates are reported compared with their N-protected counterparts. Herein we report that N-unprotected trifluoromethyl ketimines are effective for C-C bond-forming reactions using Mannich-type reactions as a model case. We demonstrate that Lewis acid catalysis was effective for promoting reactions with various N-unprotected trifluoromethyl ketimines, and thiourea organocatalysis was effective for promoting highly enantioselective reactions with various carbonyl nucleophiles, providing direct access to various N-unprotected α- and/or β-tetrasubstituted amino acid esters. Furthermore, direct construction of vicinal tetrasubstituted chiral carbon stereocenters was achieved for the first time in a highly enantio- and diastereoselective manner. These results demonstrate the potential of N-unprotected ketimines as substrates applicable to many other addition reactions.

Quinine-Based Trifunctional Organocatalyst for Tandem Aza-Henry Reaction-Cyclization: Asymmetric Synthesis of Spiroxindole-Pyrrolidine/Piperidines

A quinine-derived trifunctional sulphonamide catalyst has been developed for the effective asymmetric organocatalytic tandem aza-Henry reaction-cyclization of isatin-derived ketimines and nitroalkane-mesylates for the synthesis of spiro-pyrrolidine/piperidine-oxindoles. Demethylation of traditional bifunctional catalyst to incorporate an additional hydrogen bonding C6'-OH group plays the key role toward remarkable enantioselectivity.

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.

Enantioselective addition of diphenyl phosphonate to ketimines derived from isatins catalyzed by binaphthyl-modified organocatalysts

Chiral binaphthyl-modified squaramide-catalyzed enantioselective addition of diphenyl phosphonate to ketimines derived from isatins has been achieved. This method affords practical and efficient access to chiral 3-amino-3-phosphonyl-substituted oxindole derivatives in high yields with excellent enantioselectivities (up to 99% ee).

Diastereoselective 1,3-Dipolar Cycloadditions of N,N'-Cyclic Azomethine Imines with Iminooxindoles for Access to Oxindole Spiro-N,N-bicyclic Heterocycles

In the presence of CuI, 1,3-dipolar cycloadditions of N,N'-cyclic azomethine imines with iminooxindoles proceeded readily and furnished novel oxindole spiro-N,N-bicyclic heterocycles in moderate to excellent chemical yields with excellent diastereoselectivities.

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.

Enantioselective construction of imidazolines having vicinal tetra-substituted stereocenters by direct Mannich reaction of α-substituted α-isocyanoacetates with ketimines

Enantioselective direct Mannich-type reaction of ketimines with α-substituted α-isocyanoacetates gave imidazolines having vicinal tetra-substituted stereocenters with high stereoselectivity.

Construction of Vicinal Tetrasubstituted Stereocenters with a C-F Bond through a Catalytic Enantioselective Detrifluoroacetylative Mannich Reaction

An efficient asymmetric detrifluoroacetylative Mannich reaction of 2-fluoro-1,3-diketones/hydrates with isatin-derived ketimines catalyzed by a chiral copper(II)-diamine complex has been realized. The reaction afforded a series of 3-substituted 3-amino-2-oxindoles bearing fluorine-containing vicinal tetrasubstituted stereocenters in high yields (up to 99%) with excellent diastereoselectivities (up to >20:1 dr) and enantioselectivities (up to 94% ee).

Cinchona alkaloid thiourea mediated asymmetric Mannich reaction of isocyanoacetates with isatin-derived ketimines and subsequent cyclization: enantioselective synthesis of spirooxindole imidazolines

The organocatalyzed asymmetric Mannich reaction of isocyanoacetates with isatin ketimines and subsequent cyclization were developed, leading to spirooxindole imidazolines in high yields and excellent stereoselectivities.