K2S2O8-mediated direct C-H heteroarylation/hydroxylation of indolin-2-ones with quinoxalin-2(1H)-ones

Herein, a K2S2O8-mediated direct heteroarylation and hydroxylation reaction between quinoxalin-2(1H)-ones with a C(sp2)-H bond and indolin-2-ones with a C(sp3)-H bond via an oxidative cross-coupling reaction has been reported. We have successfully established a feasible and concise reaction system that represents the first example of free-radical-promoted heteroarylation and hydroxylation reaction on the C-3 position of oxindole. A series of 3-substituted 3-hydroxyoxindoles are obtained in 0-83% yield using this methodology.

Asymmetric Henry Reaction of Nitromethane with Substituted Aldehydes Catalyzed by Novel In Situ Generated Chiral Bis(β-Amino Alcohol-Cu(OAc)2·H2O Complex

Novel chiral thiophene-2,5-bis(β-amino alcohol) ligands (L1–L5) were designed and synthesized from thiophene-2,5-dicarbaldehyde (3) with chiral β-amino alcohols (4a–e) in 4 steps with overall 23% yields. An in situ generated L-Cu(OAc)2·H2O catalyst system was found to be highly capable catalyst for the asymmetric Henry reaction of nitromethane (7) with various substituted aromatic aldehydes (6a–m) producing chiral nitroaldols product (8a–m) with excellent enantiomeric purity (up to 94.6% ee) and up to >99% chemical yields. 20 mol% of L4-Cu(OAc)2 catalyst complex in EtOH was effective for the asymmetric Henry transformation in 24 h, at ambient temperature. Ease of ligand synthesis, use of green solvent, base free reaction, mild reaction conditions, high yields and excellent enantioselectivity are all key factors that make this catalytic system robust and highly desirable for the access of versatile building block β-nitro alcohol in practical catalytic usage via asymmetric Henry reaction.

Synthesis of Biologically Relevant 1,2,3- and 1,3,4-Triazoles: From Classical Pathway to Green Chemistry

Green Chemistry has become in the last two decades an increasing part of research interest. Nonconventional «green» sources for chemical reactions include micro-wave, mechanical mixing, visible light and ultrasound. 1,2,3-triazoles have important applications in pharmaceutical chemistry while their 1,2,4 counterparts are developed to a lesser extent. In the review presented here we will focus on synthesis of 1,2,3 and 1,2,4-triazole systems by means of classical and « green chemistry » conditions involving ultrasound chemistry and mechanochemistry. The focus will be on compounds/scaffolds that possess biological/pharmacophoric properties. Finally, we will also present the formal cycloreversion of 1,2,3-triazole compounds under mechanical forces and its potential use in biological systems.

Mononitration of a Calix[4]arene Methylene Bridge: Synthesis and Preliminary Catalysis Performances of Bridging Chiral p-tert-Butylcalix[4]arenes with a Monoamino Bridge Substituent in a 1,3-Alternate Conformation

In order to prepare bridging chiral p-tert-butylcalix[4]crown-5 with a mononitro bridge substituent in a 1,3-alternate conformation, a mononitration method of calix[4]arene bridging methylene has been first developed with tert-butyl nitrite as a nitration reagent. The effects of solvent, reaction temperature, reaction time, and nitration reagent dosage on bridge mononitration have been deeply explored to obtain an optimal nitration condition. The facile nitration presents a new key for calix[4]arene bridge derivatization. After further modification and diastereoisomeric resolution, a pair of bridging chiral p-tert-butylcalix[4]arenes with a monoamino bridge substituent were produced from the bridge-mono-nitrated calix[4]arene. Their preliminary catalysis results in the Henry reaction show good catalytic activities (up to 95% yield) and still low but obviously enhanced enantioselectivities (up to 22.3% ee from 7a, 6% ee from 1), which confirms that the structural transformation indeed improves asymmetric catalysis performances of bridging chiral calix[4]crown-5 amines in a 1,3-alternate conformation.

One-pot enantioselective synthesis of (S)-spirobrassinin and non-natural (S)-methylspirobrassinin from amino acids using a turnip enzyme

The enantioselective synthesis of (S)-(-)-spirobrassinin, which features a unique sulfur-containing spirooxindole skeleton, was achieved by focusing on the phytoalexin generation in Brassicaceae plants. Specifically, (S)-(-)-spirobrassinin was obtained in a one-pot fashion from L-tryptophan through a reaction involving S-spirocyclization with various turnip enzymes and constituents, i.e., using the turnip as a reaction reagent, catalyst, and reaction vessel. Surprisingly, this strategy also enabled the one-pot enantioselective synthesis of the novel non-natural spirooxindole (S)-(-)-5-methylspirobrassinin from 5-methyl-DL-tryptophan.

Enantioselective Henry Reaction Catalyzed by Copper(II) Complex of Bis(trans-cyclohexane-1,2-diamine)-Based Ligand

Copper(II) complex of the ligand possessing two enantiomerically pure trans-cyclohexane-1,2-diamine units proved to be an efficient catalyst for the enantioselective Henry reaction of aromatic aldehydes with nitromethane. The effect of various reaction conditions on yield and enantioselectivity of the Henry reaction was studied. The results suggest that only one cyclohexane-1,2-diamine unit is involved in catalysis of the Henry reaction.

Thiohydantoin and Hydantoin Derivatives from the Roots of Armoracia rusticana and Their Neurotrophic and Anti-neuroinflammatory Activities

Two new thiohydantoins (1 and 3) and three new hydantoins (2, 4, and 5) along with three known compounds (6-8) were isolated from roots of horseradish. Physical data analysis including NMR (¹H and ¹³C NMR, ¹H-¹H COSY, HSQC, and HMBC), HRESIMS, and ECD were employed for structure elucidation of the new compounds 1-5. Potential neuroprotective effects of all compounds (1-8) on nerve growth factor (NGF) induction in C6 glioma were also evaluated. Among these compounds, 1b and 2a exhibited potent NGF secretion stimulation activities (NGF secretion levels: 153.59 ± 5.44% and 141.99 ± 5.21%, respectively). Their anti-neuroinflammatory activities were also assessed based on their inhibitory effects on nitric oxide (NO) production in lipopolysaccharide-stimulated murine microglia. Compound 7 marginally inhibited NO production with an IC₅₀ value of 32.6 μM.

Catalytic enantioselective radical coupling of activated ketones with N-aryl glycines

Asymmetric H-bonding catalysis as a viable strategy for enantioselective radical coupling of ketones is demonstrated. With a visible-light-mediated dual catalytic system involving a dicyanopyrazine-derived chromophore (DPZ) photosensitizer and a chiral phosphoric acid (CPA), N-aryl glycines with a variety of 1,2-diketones and isatins underwent a redox-neutral radical coupling process and furnished two series of valuable chiral 1,2-amino tertiary alcohols in high yields with good to excellent enantioselectivities (up to 97% ee). In this catalysis platform, the formation of neutral radical intermediates between ketyl and H-bonding catalyst CPA is responsible for presenting stereocontrolling factors. Its success in this work should provide inspiration for expansion to other readily accessible ketones to react with various radical species, thus leading to a productive approach to access chiral tertiary alcohol derivatives.

Alkaloid Synthesis Using Organocatalysts

This chapter covers the literature since the advent, in the 21st century, of total syntheses of alkaloids using enantio- or diastereoselective organocatalytic reactions to construct the alkaloid scaffolds. The details of these alkaloid syntheses are described separately for each basic skeleton, including indole, indoline, oxindole, and piperidine alkaloids.

Photoredox-catalyzed direct aminoalkylation of isatins: diastereoselective access to 3-hydroxy-3-aminoalkylindolin-2-ones analogues

A practical protocol for the direct aminoalkylation of isatins with tetrahydroisoquinolines and other aminesviaa photoredox catalyzed radical–radical cross-coupling process is described.

Organocatalytic asymmetric Henry reaction of 1H-pyrrole-2,3-diones with bifunctional amine-thiourea catalysts bearing multiple hydrogen-bond donors

For the first time, a catalytic asymmetric Henry reaction of 1H-pyrrole-2,3-diones was achieved with a chiral bifunctional amine-thiourea as a catalyst possessing multiple hydrogen-bond donors. With this developed method, a range of 3-hydroxy-3-nitromethyl-1H-pyrrol-2(3H)-ones bearing quaternary stereocenters were obtained in acceptable yield (up to 75%) and enantioselectivity (up to 73% ee).

Silver comes into play: Henry reaction and domino cycloisomerisation sequence catalysed by [Ag(i)(Pc-L)] complexes

The Ag(i) complexes of pyridine-containing ligands with an active pendant arm are new catalysts for an old reaction: the nitroaldol condensation. When the substrates are 2-alkynylarylaldehydes, a smart cascade cycloisomerisation process can occur.

Equilibrium acidities of cinchona alkaloid organocatalysts bearing 6′-hydrogen bonding donors in DMSO

The pK_a values of 18 cinchona alkaloid based organocatalysts bearing 6′-hydrogen bonding donors were determined by the overlapping indicator method in DMSO via UV spectrophotometric titrations. The pK_a values are in the range of 6.76–20.24.

Catalyst-free synthesis of α1-oxindole-α-hydroxyphosphonates via phospha-aldol reaction of isatins employing N-heterocyclic phosphine (NHP)-thiourea

A catalyst-free phospha-aldol reaction of isatins with NHP-thiourea has been developed and the critical role of the Brønsted acid in this transformation is unveiled.

Cu (II)-catalyzed asymmetric henry reaction with a novel C1-symmetric aminopinane-derived ligand

A novel C₁-symmetric dinitrogen ligand was synthesized in high yield from commercially available (1R,2R,3R,5S)-(−)-isopinocampheylamine and 1-methyl-2-imidazolecarboxaldehyde. In combination with Cu(OAc)₂∙H₂O, this new ligand promote the reaction between nitromethane and aliphatic aldehydes with high yields (up to 97%) and moderate enantioselectivities (up to 67% ee). The reactions with benzaldehyde required prolonged reaction time that resulted in diminished yields, but accompanied with ee-values in the 55%–76% range.

An efficient aldol-type direct reaction of isatins with TMSCH2CN

Cesium fluoride catalyzed direct cyanomethylation of various isatins by using trimethylsilyl acetonitrile (TMSAN) as a nucleophile has been developed. The reaction has been explored for a number of isatins, with various substitutions on its aromatic ring. Further, the versatility of the reaction is demonstrated by converting the direct aldol adducts to various corresponding intermediates.

Lanthanide derivatives comprising arylhydrazones of β-diketones: cooperative E/Z isomerization and catalytic activity in nitroaldol reaction

RAHB and ionic interaction assisted E/Z→E isomerization of arylhydrazone of β-diketone is reported.

Organocatalytic enantioselective aza-Henry reaction of ketimines derived from isatins: access to optically active 3-amino-2-oxindoles

An organocatalytic asymmetric aza-Henry reaction of ketimines derived from isatins with nitroalkanes has been achieved using Cinchona alkaloid organocatalysts.