Enantioselective Synthesis of Biphenyl-Bridged ϵ-Sultams by Organocatalytic Mannich Reactions of Cyclic N-Sulfonylimines with Unactivated Ketones

A highly enantioselective Mannich reaction of biphenyl-bridged seven-membered cyclic N-sulfonylimines with methyl alkyl ketones is disclosed in this study. The reaction was performed under organocatalysis by using a quinine-derived primary amine as the catalyst in combination with a Brønsted acid as the co-catalyst. High yields (up to 89 %) and excellent enantioselectivities (up to 97 % ee) were observed. For methyl alkyl ketones containing a larger alkyl substituent, specific regioselective addition to the C=N bond is favored at the methyl group. On the contrary, ketones containing a smaller alkyl substituent or hydroxyacetone substrates gave major syn selective Mannich products at the methylene group.

Organocatalytic Enantioselective γ-Position-Selective Mannich Reactions of β-Ketocarbonyl Derivatives

Catalytic asymmetric Mannich reactions of β-ketocarbonyl derivatives (such as β-ketoesters and (2-oxopropyl)phosphonate), resulting in the formation of a C–C bond at the γ-position of the β-ketocarbonyl derivatives with high enantioselectivities, are reported. The bond formation at the α-position of the β-ketoester was reversible, and the γ-position-reacted product δ-amino β-ketoester derivative was kinetically formed and was stable. The dynamic kinetic process was key for the direct access to the γ-position-reacted products from β-ketocarbonyls under catalytic conditions.

Exploiting Anion-π Interactions for Efficient and Selective Catalysis with Chiral Molecular Cages

Exploiting anion-π interactions in catalyst design is a fascinating direction to develop new and fundamental catalysis. For the appealing yet flexible π-face activation, can two or more π-acidic surfaces be manipulated for cooperative activation to achieve efficient transformation and particularly selectivity control is highly desirable. Here, we demonstrate a supramolecular π-catalysis strategy by establishing cooperative π-face activation in a confined electron-deficient cage cavity. The catalysts have a triazine based prism-like cage core and pendant chiral base sites. Only 2 mol % of cage catalyst efficiently catalyzed the decarboxylate Mannich reactions of sulfamate-headed cyclic aldimines and a series of malonic acid half thioesters in nearly quantitative yields and up to 97 % ee, enabling an unprecedent organocatalytic approach. The supramolecular π-cavity is essential in harnessing cooperative anion-π interactions for the efficient activation and excellent selectivity control.

Bifunctional amino sulfonamide-catalyzed asymmetric conjugate addition to alkenyl alkynyl ketimines as enone surrogates

A bifunctional amino sulfonamide-catalyzed asymmetric conjugate addition of aldehydes to alkenyl alkynyl ketimines as reactive surrogates for enones has been developed. Use of a phenylcyclopropane-based amino sulfonamide catalyst, which can activate and orient the ketimines through hydrogen bonding, affords the desired conjugate adducts with high chemo-, diastereo- and enantioselectivity.

Construction of chiral α-tert-amine scaffolds via amine-catalyzed asymmetric Mannich reactions of alkyl-substituted ketimines

Stereoselective Mannich reactions of aldehydes with ketimines provide chiral β-amino aldehydes that bear an α-tert-amine moiety. However, the structural variation of the ketimines is limited due to the formation of inseparable E/Z isomers, low reactivity, and other synthetic difficulties. In this study, a highly diastereodivergent synthesis of hitherto difficult-to-access β-amino aldehydes that bear a chiral α-tert-amine moiety was achieved using the amine-catalyzed Mannich reactions of aldehydes with less-activated Z-ketimines that bear both alkyl and alkynyl groups.

C2-Symmetric 1,2-Diphenylethane-1,2-diamine-Derived Primary-Tertiary Diamine-Catalyzed Asymmetric Mannich Addition of Cyclic N-Sulfonyl Trifluoromethylated Ketimines

A simple chiral primary-tertiary diamine derived from C₂-symmetric 1,2-diphenylethane-1,2-diamine as the organocatalyst in combination with the trifluoroacetic acid additive for the asymmetric Mannich reaction of cyclic N-sulfonyl trifluoromethylated ketimines and methyl ketones afforded the desired product with high enantioselectivity (73-96% ee). The reactions proceeded well for a variety of different substituted cyclic N-sulfonyl trifluoromethyl ketimines and various alkyl methyl ketones, providing access to diverse enantioenriched benzo-fused cyclic sulfamidate N-heterocycles bearing a trifluoromethylated α-tetrasubstituted carbon stereocenter. This study also investigated the diastereoselective reduction of the carbonyl group and ring cleavage reduction of the sulfamidate group of the corresponding Mannich product.

Enantioselective (3+2) cycloaddition via N-heterocyclic carbene-catalyzed addition of homoenolates to cyclic N-sulfonyl trifluoromethylated ketimines: synthesis of fused N-heterocycle γ-lactams

An enantioselective (3+2) cycloaddition of enals and cyclic N-sulfonyl trifluoromethyl ketimines via N-heterocyclic carbene-catalyzed homoenolate addition is described. This reaction can efficiently construct fused N-heterocycle γ-lactams bearing two adjacent chiral centers with >20 : 1 dr and 94-99% ee, with one chiral center as a trifluoromethylated α-tetrasubstituted carbon stereocenter.

Cyclic imines – preparation and application in synthesis

Cyclic imines, available from various nitrogen-containing reactants, serve as versatile synthetic intermediates for biologically active compounds.

Enantioselective organocatalytic Michael additions of N,N'-dialkylbarbituric acids to enones

N,N'-Dialkylbarbituric acids as cyclic malonamide donors were successfully used in the enantioselective Michael addition reaction of enones. Using cinchona alkaloid-based bifunctional squaramide as an organocatalyst, this Michael reaction of N,N'-di-tert-butylbarbituric acid with various enones features a highly enantioselective (91-99% ee) production of the corresponding optically active 5-substituted barbituric acid derivatives. The transformations of the Michael product for the barbituric acid structural unit were realized in two ways, deprotection to remove the N-tert-butyl group and alkylation to produce 5,5-disubstituted barbituric acid derivatives.

A phosphotungstic acid-supported multifunctional organocatalyst containing 9-amino(9-deoxy)epi-cinchonidine and Brønsted acid and its application in asymmetric aldol reaction

Phosphotungstic acid-supported multifunctional 9-amino(9-deoxy)epi-cinchonidine containing Brønsted acid was developed through facile precipitation for the first time and afforded aldol adducts in excellent catalytic performance with good reusability.

Enantioselective alkynylation of benzo[e][1,2,3]-oxathiazine 2,2-dioxides catalysed by (R)-VAPOL-Zn complexes: synthesis of chiral propargylic cyclic sulfamidates

An enantioselective alkynylation of cyclic benzoxathiazine 2,2-dioxides catalysed by (R)-VAPOL-Zn(ii) complexes is described.

Organocatalytic enantioselective aza-Friedel–Crafts reaction of 2-naphthols with benzoxathiazine 2,2-dioxides

An organocatalytic enantioselective aza-Friedel–Crafts addition of 2-naphthols to benzoxathiazine 2,2-dioxides is described using a quinine-derived bifunctional catalyst.