Bifunctional Amine-Squaramides: Powerful Hydrogen-Bonding Organocatalysts for Asymmetric Domino/Cascade Reactions

Self-assembled fibrillar networks of a multifaceted chiral squaramide: supramolecular multistimuli-responsive alcogels

Chiral N,N'-disubstituted squaramide has been found to undergo self-assembly in a variety of alcoholic solvents at low concentrations leading to the formation of novel nanostructured supramolecular alcogels. The gels responded to thermal, mechanical, optical and chemical stimuli. Solubility studies, gelation ability tests and computer modeling of a series of structurally related squaramides proved the existence of a unique combination of non-covalent molecular interactions and favorable hydrophobic/hydrophilic balance in that drive the anisotropic growth of alcogel networks. The results have also revealed a remarkable effect of ultrasound on both the gelation kinetics and the properties of the alcogels.

Stereocontrolled Construction of Tetrahydropyrano[2,3-c]pyrazole Scaffold via an Organocatalyzed Formal [3 + 3] Annulation

A bifunctional squaramide catalyzed enantioselective formal [3 + 3] annulation reaction with pyrazolin-5-ones and nitroallylic acetates has been developed. Densely substituted tetrahydropyrano[2,3-c]pyrazoles with two adjacent stereogenic centers are obtained in a highly stereocontrolled manner. Representative transformation of the annulation product to a biologically important fused dihydroisoquinoline is achieved without any appreciable loss in the diastereo- and enantioselectivity.

Asymmetric Organocatalytic Wittig [2,3]-Rearrangement of Oxindoles

A highly enantioselective organocatalytic [2,3]-rearrangement of oxindole derivatives is presented. The reaction was catalyzed by squaramide, and this provides access to 3-hydroxy 3-substituted oxindoles in high enantiomeric purities.

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

Organocatalysis, now running its second decade of life, is being considered one of the main tools a synthetic chemist has to perform asymmetric catalysis. In this review the synthesis of six-membered rings, that contain multiple chiral centers, either by a ring closing process or by a functionalization reaction on an already existing six-membered ring, utilizing bifunctional (thio)ureas will be summarized. Initially, the use of primary amine-thioureas as organocatalysts for the above transformation is being discussed, followed by the examples employing secondary amine-thioureas. Finally, the use of tertiary amine-thioureas and miscellaneous examples are presented.

A quadruple cascade protocol for the one-pot synthesis of fully-substituted hexahydroisoindolinones from simple substrates

A new and efficient synthetic method to obtain fully-substituted hexahydroisoindolinones was developed by using bifunctional tertiary amine-thioureas as powerful catalysts. As far as we know, there is no efficient synthetic method developed toward fully-substituted hexahydroisoindolinones. The products were obtained in good yield and diastereoselectivity. The one-pot cascade quadruple protocol features readily available starting materials, simple manipulation, mild conditions and good atom economy.

Discovery and enantiocontrol of axially chiral urazoles via organocatalytic tyrosine click reaction

Axially chiral compounds play an important role in areas such as asymmetric catalysis. The tyrosine click-like reaction is an efficient approach for synthesis of urazoles with potential applications in pharmaceutical and asymmetric catalysis. Here we discover a class of urazole with axial chirality by restricted rotation around an N-Ar bond. By using bifunctional organocatalyst, we successfully develop an organocatalytic asymmetric tyrosine click-like reaction in high yields with excellent enantioselectivity under mild reaction conditions. The excellent remote enantiocontrol of the strategy originates from the efficient discrimination of the two reactive sites in the triazoledione and transferring the stereochemical information of the catalyst into the axial chirality of urazoles at the remote position far from the reactive site.

Chiral Triazoles in Anion-Binding Catalysis: New Entry to Enantioselective Reissert-Type Reactions

Easily accessible and tunable chiral triazoles have been introduced as a novel class of C-H bond-based H-donors for anion-binding organocatalysis. They have proven to be effective catalysts for the dearomatization reaction of different N-heteroarenes. Although this dearomatization approach represents a powerful strategy to build chiral heterocycles, to date only a few catalytic methods to this end exist. In this work, the organocatalyzed enantioselective Reissert-type dearomatization of isoquinoline derivatives employing a number of structurally diverse chiral triazoles as anion-binding catalysts was realized. The here presented method was employed to synthesize a number of chiral 1,2-dihydroisoquinoline substrates with an enantioselectivity up to 86:14 e.r. Moreover, a thorough study of the determining parameters affecting the activity of this type of anion- binding catalysts was carried out.

Rawal's catalyst as an effective stimulant for the highly asymmetric Michael addition of β-keto esters to functionally rich nitro-olefins

A general approach to the asymmetric synthesis of highly substituted dihydroquinolines was achieved through neighboring ortho-amino group engaged sequential Michael/amination/dehydration reactions.

Organocatalytic cascade Michael/Michael reaction for the asymmetric synthesis of spirooxindoles containing five contiguous stereocenters

Squaramide-catalyzed cascade Michael/Michael reaction for the asymmetric synthesis of five-membered spirooxindoles containing five contiguous stereocenters is presented.

Synthesis of luminescent squaramide monoesters: cytotoxicity and cell imaging studies in HeLa cells

Luminescent squaramide monoesters functionalised with fluorophore groups have been explored as cytotoxic and imaging agents. The biodistribution behaviour differs depending on the fluorescent moiety; lysosomal and nuclear localisation have been observed.

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.

Current advances of organocatalytic Michael–Michael cascade reaction in the synthesis of highly functionalized cyclic molecules

Organocatalytic domino/cascade reactions provide a convenient method for the construction of highly functionalized cyclic molecular structures bearing multiple stereocenters in a highly stereoselective fashion.

Organocatalytic asymmetric addition of alcohols to cyclic trifluoromethyl ketimines: highly enantioselective synthesis of chiral N,O-ketals

A highly enantioselective addition of alcohols to cyclic trifluoromethyl ketimines catalyzed by quinine-thiourea is developed.

The enantioselective construction of chiral spirooxindole-based 4-thiazolidinone via asymmetric catalytic formal [3+2] annulation using a bifunctional catalyst

A facile and efficient method based on the asymmetric [3+2] annulation of 1,4-dithiane-2,5-diol to ketimines for the construction of chiral spirooxindole-based 4-thiazolidinone was reported.

Effective and novel enantioselective preparation of pyranopyrazoles and pyranocoumarins that is catalyzed by a quinine-derived primary amine

In this study, we executed an effective and novel enantioselective Michael/cyclodehydration sequential reaction between pyrazolin-5-one (or 4-hydroxy-2-pyrone) and chalcones that is catalyzed by a quinine-derived primary amine L7 in the presence of Boc-d-Phg-OH.

A novel calix[4]arene-based bifunctional squaramide organocatalyst for enantioselective Michael addition of acetylacetone to nitroolefins

A new chiral calix[4]arene-based organocatalyst 3 bearing bis-squaramide moieties was designed and synthesized from p-tert-butylcalix[4]arene. This bifunctional organocatalyst was used in the enantioselective conjugate addition of acetyl acetone to β-nitrostyrenes. The corresponding adducts were obtained in good to excellent yields with high enantioselectivities.

Bifunctional tertiary amine-squaramide catalyzed asymmetric catalytic 1,6-conjugate addition/aromatization of para-quinone methides with oxindoles

A novel organocatalytic enantioselective 1,6-addition of p-QMs has been developed to access diarylmethine-functionalized oxindoles bearing vicinal tertiary and quaternary stereocenters.

Asymmetric dual catalysis via fragmentation of a single rhodium precursor complex

A strategy for dual transition metal catalysis and organocatalysis is reported via disintegration of a single rhodium complex. Conveniently, the chiral-at-metal rhodium precatalyst can be synthesized in just two steps starting from rhodium trichloride without the need for any chromatography.

Design and synthesis of squaramide-based MOFs as efficient MOF-supported hydrogen-bonding organocatalysts

Herein, we utilize a new, squaramide-based ligand, combined with a postsynthetic exchange (PSE) synthetic approach to prepare a series of Cu(ii)–squaramide MOFs that are active catalysts for the Friedel–Crafts reaction.

Organocatalyzed enantioselective [3 + 3] annulation for the direct synthesis of conformationally constrained cyclic tryptophan derivatives

Synthesis of optically active conformationally strained β-branched cyclic tryptophan derivatives has been realized via chiral squaramide catalyzed enantioselective formal [3 + 3] annulation of indolin-2-thiones and 4-arylmethylideneoxazolin-5(4H)-ones.

A new series of bipyridine based chiral organocatalysts for enantioselective Henry reaction

We report the design and synthesis of a new series of binaphthol based chiral organocatalysts which can act as metal-free organocatalysts in the enantioselective Henry reaction with very good yield and ee.

Enantioselective construction of novel chiral spirooxindoles incorporating a thiazole nucleus

Enantioselective synthesis of novel thiazole-fused spirooxindoles has been realized via chiral thiourea catalyzed asymmetric cascade Michael addition/cyclization of thiazolones and 3-ylideneoxindoles.

Squaramides with cytotoxic activity against human gastric carcinoma cells HGC-27: synthesis and mechanism of action

A series of squaramates and squaramides have been synthesized and their cytotoxic activity has been investigated in different cancer cell lines.

Organocatalytic asymmetric Michael addition of α-alkylidene succinimides to nitrostyrenes

A squaramide-catalyzed asymmetric Michael addition of α-alkylidene succinimides to nitrostyrenes for the synthesis of chiral succinimide derivatives was described.

Enantioselective synthesis of chiral α,β-unsaturated γ-substituted butyrolactams by organocatalyzed direct asymmetric vinylogous Michael addition of α,β-unsaturated γ-butyrolactam to 2-enoylpyridines

Approach providing a series of optically active α,β-unsaturated γ-substituted butyrolactams in high yields with excellent diastereo- and enantioselectivities.

Asymmetric Synthesis of Spiropyrazolones by Sequential Organo- and Silver Catalysis

A stereoselective one-pot synthesis of spiropyrazolones through an organocatalytic asymmetric Michael addition and a formal Conia-ene reaction has been developed. Depending on the nitroalkene, the 5-exo-dig-cyclization could be achieved by silver-catalyzed alkyne activation or by oxidation of the intermediate enolate. The mechanistic pathways have been investigated using computational chemistry and mechanistic experiments.