Enantioselective Construction of Chiral Bispiro[Oxindole-Pyrrolidine-Pyrazolone] Derivatives via Sequential and One-Pot Mannich/Hydroamination Reaction

Asymmetric Organocatalytic [3 + 2]-Cycloaddition of N-Alkoxy-4-oxo-acrylamides with Isatin-Derived Ketimines: Access to Enantioselective Synthesis of Spirooxindole-imidazolidinones

The spirooxindole framework is a privileged motif in numerous biologically significant natural products and has been demonstrated as a crucial core scaffold in a variety of medicinally significant compounds. Herein, we achieved a highly efficient enantioselective [3 + 2]-cycloaddition reaction of N-alkoxy-4-oxo-acrylamides with isatin-derived ketimines. This method enabled the precise synthesis of chiral spirooxindole-imidazolidinone derivatives, which are notable for their intricate structures and the presence of chiral quaternary centers. Our approach utilized an organocatalytic strategy with a hydrogen-bonding bifunctional squaramide-based catalyst. This reaction demonstrated impressive results, achieving high yields and exceptional enantioselectivities of >99% ee for the majority of substrates, even when employing only 2 mol % of the catalyst.

Enantioselective merged gold/organocatalysis

Gold complexes, because of their unique carbophilic nature, have evolved as efficient catalysts for catalyzing various functionalization reactions of C-C multiple bonds. However, the realization of enantioselective transformations via gold catalysis remains challenging due to the geometrical constraints and coordination behaviors of gold complexes. In this context, merged gold/organocatalysis has emerged as one of the intriguing strategies to achieve enantioselective transformations which could not be possible by using a single catalytic system. Historically, in 2009, this field started with the merging of gold with axially chiral Brønsted acids and chiral amines to achieve enantioselective transformations. Since then, based on the unique reactivity profiles offered by each catalyst, several reports utilizing gold in conjunction with various chiral organocatalysts such as amines, Brønsted acids, N-heterocyclic carbenes, hydrogen-bonding and phosphine catalysts have been documented in the literature. This article demonstrates an up-to-date development in this field, especially focusing on the mechanistic interplay of gold catalysts with chiral organocatalysts.

Organocatalytic Asymmetric [4 + 2]-Cycloadditions of 2-Aminophenyl Enones with Isatin-Derived Ketimines: Diastereo- and Enantioselective Synthesis of Spirooxindole-Tetrahydroquinazolines

A novel method for the enantioselective synthesis of spiro N,N-heterocyclic oxindoles has been developed, employing asymmetric [4 + 2]-cycloadditions of 2-aminophenyl enones with isatin-derived ketimines. This method employs an organocatalytic approach, utilizing a bifunctional squaramide-based catalyst. It enables the precise synthesis of chiral spirooxindole-tetrahydroquinazolines with intricate structures, featuring chiral quaternary centers. This process achieves remarkable results, including high yields and exceptional levels of enantioselectivity and diastereoselectivity (up to 96% yield, 95% ee, and >20:1 dr).

Synthesis of novel pyrazolone candidates with studying some biological activities and in-silico studies

Pyranopyrazole derivatives have a vital role in the class of organic compounds because of their broad spectrum of biological and pharmacological importance. Our current goal is the [3 + 3] cycloaddition of benzoyl isothiocyanate and pyrazolone 1 to undergo oxidation cyclization, producing pyrazoloxadiazine 3. The diol 5 was obtained as a condensation of two equivalents of 1 with thiophene-2-carboxaldehyde in acetic acid above the sodium acetate mixture. When the condensation was carried out in piperidine under fusion, unsaturated ketone 4 was obtained. The pyrazolo pyran derivative 11 resulted from the [3 + 3] cycloaddition of 1 and cinnamic acid, while the Pyrone derivative was prepared by acylation of 12 with two equivalents of acetic anhydride. Phthalic anhydride undergoes arylation using zinc chloride as a catalyst. The cyclic keto acid 23 was synthesized by the action of succinic anhydride on 12 in the acetic medium, while the latter reacted with cinnamic acid, leading to pyrazole derivative 24. All of these reactions were through the Michael reaction mechanism. All the tested compounds showed good antimicrobial activity against pathogenic microorganisms; newly synthesized compounds were also screened for their antioxidant activity. Rational studies were carried out by the ABTs method to allow a broader choice of activities. In addition, similar off-compounds were conducted. Molecular docking studies with the CB-Dock server and MD simulations were created with the default settings of the Solution Builder on the CHARMM-GUI server at 150 nm. A good correlation was obtained between the experimental results and the theoretical bioavailability predictions using POM theory.

Access to Spirooxindole-Fused Cyclopentanes via a Stereoselective Organocascade Reaction Using Bifunctional Catalysis

The present study reports an asymmetric organocascade reaction of oxindole-derived alkenes with 3-bromo-1-nitropropane efficiently catalyzed by the bifunctional catalyst. Spirooxindole-fused cyclopentanes were produced in moderate-to-good isolated yields (15-69%) with excellent stereochemical outcomes. The synthetic utility of the protocol was exemplified on a set of additional transformations of the corresponding spirooxindole compounds.

Enantioselective Synthesis of Spiro Heterocyclic Compounds Using a Combination of Organocatalysis and Transition-Metal Catalysis

Over the last ten years, the combination of organocatalysis with transition metal (TM) catalysis has become one of the most important toolboxes used for synthesizing optically pure compounds containing chiral quaternary centers, including spiro heterocyclic molecules. The dominant method in the enantioselective synthesis of spiro heterocyclic compounds based on synergistic catalysis includes chiral aminocatalysis and NHC catalysis, as already established covalent organocatalytic strategies. Another area of organocatalysis widely combined with TM catalysis producing enantiomerically enriched spiro heterocyclic compounds is non-covalent catalysis, dominated by chiral phosphoric acids, thiourea, and squaramide derivatives. This review article aims to summarize enantioselective methods used for constructing spirocyclic heterocycles based on a combination of organocatalysis and transition metal catalysis.

Stereoselective N-Heterocyclic-Carbene-Catalyzed Formal [4 + 2] Cycloaddition: Access to Chiral Heterocyclic Cyclohexenones

The present study reports an asymmetric NHC-catalyzed formal [4 + 2] cycloaddition of heterocyclic alkenes containing a polarized double bond with an azolium-dienolate intermediate generated from α-bromo-α,β-unsaturated aldehydes without external oxidation of the Breslow intermediate. Heterocyclic cyclohexenones were produced in good isolated yields (typically about 90%) with good stereochemical outcomes (in most cases, dr > 20/1, and ee = 70-99%). The synthetic utility of the protocol was exemplified by the scope of heterocyclic alkenes.

Catalytic asymmetric addition to cyclic N-acyl-iminium: access to sulfone-bearing contiguous quaternary stereocenters

Herein, we report the first chiral phosphoric acid (CPA)-catalyzed asymmetric addition of α-fluoro(phenylsulfonyl)methane (FSM) derivatives to in situ generated cyclic N-acyliminium. This process enables metal-free expeditious access to sulfone and fluorine incorporating contiguous all substituted quaternary stereocenters ingrained in biorelevant isoindolinones in excellent stereoselectivities (up to 99% ee and up to 50 : 1 dr).

Catalytic asymmetric [3 + 2] cycloaddition of pyrazolone-derived MBH carbonate: highly stereoselective construction of the bispiro-[pyrazolone-dihydropyrrole-oxindole] skeleton

A catalytic asymmetric construction of the bispiro[pyrazolone-dihydropyrrole-oxindole] skeleton catalyzed by chiral DMAP-derived catalyst was successfully achieved by employing recently explored pyrazolone-derived MBH carbonate in high yields with excellent stereoselectivities. The proposed transition state indicated that the intermolecular hydrogen bonds and π-π interactive forces played an essential role in stereoselective chemical transformation.

Dinuclear zinc catalyzed asymmetric [3 + 2] spiroannulation for the synthesis of diverse bispirocyclic saccharines

A highly atom-economical and novel enantioselective [3 + 2] spiroannulation reaction of saccharine-derived cyclic 1-azadienes with α-hydroxy-1-indanones has been developed.