Diversity-Oriented Synthesis of Spiro[chromeno[2,3-b]pyridine-3,4'-pyrazole] Derivatives via Pseudo-Three-Component Reactions

A novel one-pot pseudo-three-component reaction of 2-amino-4H-chromen-4-ones with 4-benzylidene-5-alkyl-2-aryl-2,4-dihydro-3H-pyrazol-3-ones was investigated for the synthesis of the spiro[chromeno[2,3-b]pyridine-3,4'-pyrazole] derivatives. This procedure involved Michael addition, elimination, and hetero-Diels-Alder sequences, affording a series of spiropyrazolone-chromeno[2,3-b]pyridines in good yields that possessed cis relationships between two aryl groups and the carbonyl of the pyrazolone unit.

Asymmetric Synthesis of Spiropyrazolone-Fused Dihydrofuran-naphthoquinones Bearing Contiguous Stereocenters via a Michael Addition/Chlorination/Nucleophilic Substitution Sequence

An enantioselective synthesis of spiropyrazolone-fused dihydrofuran-naphthoquinones is first demonstrated via a Michael addition/Chlorination/Nucleophilic substitution sequence. The reactions of 2-hydroxy-1,4-naphthoquinone and α,β-unsaturated pyrazolones in the presence of the cinchona alkaloid derived hydrogen-bonding catalyst and NCS provide spiropyrazolone-fused 2,3-dihydronaphtho[2,3-b]furan-4,9-diones bearing contiguous stereocenters, of which one is the spiro quaternary stereocenter in high yields with exclusive diastereoselectivity and good to excellent enantioselectivities.

The chemistry of 2-hydroxy-β-nitrostyrenes: versatile intermediates in synthetic organic chemistry

The applications of 2-hydroxy-β-nitrostyrenes as efficient bifunctional intermediates in organic synthesis are investigated in this review. For this purpose, reactions of 2-hydroxy-β-nitrostyrenes with diverse molecules, including carbonyl compounds, 1,3-dicarbonyl compounds, α,β-unsaturated carbonyl compounds, hemiacetals, nitroalkenes, γ-butenolides, tetronic acid, azalactones, pyrazolones, enamines, malononitrile, methyleneindolinones, ylides, etc., were investigated to construct interesting biologically active scaffolds such as chromans, chromenes, coumarins, benzofurans and their fused and spiro rings, natural products, and other useful cyclic and acyclic compounds. The main focus is on the asymmetric synthesis of these compounds via cascade/domino/tandem reactions catalyzed by chiral organocatalysts. In this review, around 60 papers reported between the years 2000 and 2022 are presented.

Synthesis of fully functionalised spiropyran pyrazolone skeletons via a formal [4 + 2] cascade process using β-nitro-styrene-derived MBH-alcohols

An efficient protocol was established to construct spiro pyrazolone tetrahydropyran scaffolds at ambient temperature under metal-free conditions. The reaction proceeded via formal [4 + 2] cyclisation of trans-β-nitro-styrene-derived Morita-Baylis-Hillman (MBH) alcohol with α-arylidene pyrazolone. The reaction followed an oxa-Michael/Michael cascade pathway, resulting in the formation of new C-C and C-O bonds. Organocatalytic synthesis of spiropyrazolones using quinine-derived catalyst resulted in 94% enantiomeric excess (ee) and excellent (>20 : 1) diastereoselectivity.

Enantioselective Michael/Hemiketalization Cascade Reactions between Hydroxymaleimides and 2-Hydroxynitrostyrenes for the Construction of Chiral Chroman-Fused Pyrrolidinediones

In this paper, the organocatalytic asymmetric Michael addition/hemiketalization cascade reactions between hydroxymaleimides and 2-hydroxynitrostyrenes were developed, which provided a new protocol for building a chiral ring-fused chroman skeleton. This squaramide-catalyzed cascade reaction provided chiral chroman-fused pyrrolidinediones with three contiguous stereocenters in good to high yields (up to 88%), with excellent diastereoselectivities (up to >20:1 dr) and enantioselectivities (up to 96% ee) at −16 °C. Moreover, a scale-up synthesis was also carried out, and a possible reaction mechanism was proposed.

Asymmetric [4 + 2] Annulation of Cyclobutenones and Pyrazolone 4,5-Diones: Access to Novel δ-Lactone-Fused Spiropyrazolones

Although numerous chiral pyrazolones with a six-membered spirocyclic center at the C4 position have been developed, the asymmetric construction of six-membered oxa-spiropyrazolones is still a challenging task in organic synthesis. Herein, we describe the [4 + 2] annulation of cyclobutanones and pyrazoline-4,5-diones for the efficient synthesis of δ-lactone-fused spiropyrazolone derivatives with generally high yields and good enantioselectivities under mild conditions. The successful scale-up synthesis and further transformation of the final product highlight the practicality and reliability of this reaction.

Synthesis and Applications of Carbohydrate-Based Organocatalysts

Organocatalysis is a very useful tool for the asymmetric synthesis of biologically or pharmacologically active compounds because it avoids the use of noxious metals, which are difficult to eliminate from the target products. Moreover, in many cases, the organocatalysed reactions can be performed in benign solvents and do not require anhydrous conditions. It is well-known that most of the above-mentioned reactions are promoted by a simple aminoacid, l-proline, or, to a lesser extent, by the more complex cinchona alkaloids. However, during the past three decades, other enantiopure natural compounds, the carbohydrates, have been employed as organocatalysts. In the present exhaustive review, the detailed preparation of all the sugar-based organocatalysts as well as their catalytic properties are described.

Diastereoselective Synthesis of Tetrabenzohydrofuran Spirooxindoles via Diethyl Phosphite-Mediated Coupling of Isatins with o-Quinone Methides

Diethyl phosphite-initiated coupling of isatins with o-quinone methides (o-QMs) is reported. This reaction involves a cascade transformation initiated by base-promoted addition of phosphite to isatins, followed by [1,2]-phospha-Brook rearrangement. This generates α-phosphonyloxy enolates that are subsequently intercepted by o-QMs and finally intramolecular ring closure. This protocol was used to diastereoselectively synthesize a range of trans-tetrabenzohydrofuran spirooxindoles in moderate to good yields with moderate to excellent diastereoselectivities.

A PPh3-catalyzed sequential annulation reaction to construct cyclopentane-fused dihydropyrazolone-pyrrolidinediones

A PPh3-catalyzed sequential cycloaddition of maleimides with unsaturated pyrazolones has been developed. This protocol provides a simple and practical strategy for the construction of dispirocyclopentyl-[dihydropyrazolone-pyrrolidinedione] pyrrolidinedione skeletons containing five contiguous stereogenic centers, including two spiro-quaternary centers, with moderate yields (34-73%) and excellent diastereoselectivities (>20 : 1).

Catalytic Asymmetric Construction of a 1,2,4-Benzotriazepine Skeleton via Diastereo- and Enantioselective Decarboxylative [4 + 3] Cyclization

We have developed a protocol for palladium-catalyzed decarboxylative [4 + 3] cycloaddition reactions between 4-vinyl benzoxazinanones and azomethine imines to generate moderate to good yields of structurally diverse 1,2,4-benzotriazepines bearing two stereogenic centers with good to excellent stereoselectivities. This protocol not only addresses the challenge of asymmetrically constructing compounds with a 1,2,4-benzotriazepine skeleton but also demonstrates the utility of decarboxylative cycloadditions for the synthesis of enantioenriched polycyclic compounds.

Chiral Thioureas-Preparation and Significance in Asymmetric Synthesis and Medicinal Chemistry

For almost 20 years, thioureas have been experiencing a renaissance of interest with the emerged development of asymmetric organocatalysts. Due to their relatively high acidity and strong hydrogen bond donor capability, they differ significantly from ureas and offer, appropriately modified, great potential as organocatalysts, chelators, drug candidates, etc. The review focuses on the family of chiral thioureas, presenting an overview of the current state of knowledge on their synthesis and selected applications in stereoselective synthesis and drug development.

Synthesis of methylene cyclopropane-fused chromenes and dihydroquinolines by sequential [4 + 2]- and [1 + 2]-annulation

A base promoted sequential [4 + 2]- and [1 + 2]-annulation of 2-hydroxychalcones or 2-tosylaminochalcones with prop-2-ynylsulfonium salts was developed.

Recent advances in organocatalytic asymmetric oxa-Michael addition triggered cascade reactions

In this review, we summarized recent advances in organocatalytic asymmetric oxa-Michael addition triggered cascade reactions.

Catalytic Asymmetric Synthesis of Spiropyrazolones and their Application in Medicinal Chemistry

Chiral spiropyrazolones are unique frameworks widely found in a large family of medicinally relevant compounds with various biological activities. Substantial research efforts have been invested toward stereoselectively by constructing spiro-cyclic structures. Over the past years, remarkable progress has been made in the organo- and metal-catalyzed asymmetric synthesis of spiropyrazolones through the utilization of accessible simple pyrazolone derivatives as raw materials. This review is organized according to the size of the spiro-ring fused at the 4-position of the pyrazolone framework. In the last part, the bio-evaluations of chiral spiropyrazolones for drug discovery are summarized.

The catalytic asymmetric synthesis of CF3-containing spiro-oxindole–pyrrolidine–pyrazolone compounds through squaramide-catalyzed 1,3-dipolar cycloaddition

Pharmaceutically important compounds were synthesized through the organocatalytic 1,3-dipolar cycloaddition reaction.

Lewis base catalyzed regioselective cyclization of allene ketones or α-methyl allene ketones with unsaturated pyrazolones

A nitrogen-containing Lewis base catalyzed highly regioselective [4 + 2] cycloaddition of allene ketones or α-methyl allene ketones with unsaturated pyrazolones has been disclosed to give the corresponding tetrahydropyrano [2,3-c] pyrazoles in moderate to good yields under mild conditions. High regioselectivity, 100% atom-economy, broad substrate scope and good functional group tolerance are attractive features of this process and make it a practical and versatile transformation.

Diastereo- and Enantioselective Syntheses of Trisubstituted Benzopyrans by Cascade Reactions Catalyzed by Monomeric and Polymeric Recoverable Bifunctional Thioureas and Squaramides

4-Vinylphenyl-substituted squaramides have been tested as organocatalysts for the diastereo- and enantioselective synthesis of trisubstituted benzopyrans via an oxa-Michael intramolecular nitro-Michael cascade reaction. Both the enantio- and diastereoselection were good to moderate, depending on the nature of the chiral scaffold in the catalyst. The diastereoselection is better for the most active catalyst because the final products epimerize at C-3 along the time. Supported squaramide sq-9 prepared by copolymerization of sq-4 with styrene and divinylbenzene is also effective in promoting the cascade reaction, and it is recoverable and reusable for five cycles maintaining the activity.

Catalytic enantioselective synthesis of carboxy-substituted 2-isoxazolines by cascade oxa-Michael-cyclization

An efficient quinidine-based phase-transfer-catalyzed enantioselective cascade oxa-Michael-cyclization reaction of hydroxylamine with various β-carboxy-substituted α,β-unsaturated ketones has been achieved for the preparation of chiral carboxy-substituted 2-isoxazolines. This cascade reaction provided the desired products in good yields (up to 98%) with excellent enantioselectivities (91-96% ee). In addition, the cascade reaction was effectively applied to the first catalytic asymmetric synthesis of the herbicide (S)-methiozolin.

Asymmetric synthesis of polysubstituted chiral chromans via an organocatalytic oxa-Michael-nitro-Michael domino reaction

A catalytic asymmetric method for the synthesis of polysubstituted chromans via an oxa-Michael-nitro-Michael reaction has been developed. The squaramide-catalyzed domino reaction of 2-hydroxynitrostyrenes with trans-β-nitroolefins produced chiral chromans with excellent enantioselectivities (up to 99% ee), diastereoselectivities (up to >20 : 1 dr), and moderate to good yields (up to 82%).

New development in the enantioselective synthesis of spiro compounds

In this review we summarize the latest developments in the enantioselective synthesis of spirocompounds. The most important organometallic and organocatalytic methodologies are highlighted.

Pyrazolone: a powerful synthon for asymmetric diverse derivatizations

This feature article reports recent advances in the asymmetric diverse derivatizations of the pyrazolone scaffold.

Bisphosphine catalyzed sequential [3 + 2] cycloaddition and Michael addition of ynones with benzylidenepyrazolones via dual α′,α′-C(sp3)–H bifunctionalization to construct cyclopentanone-fused spiro-pyrazolones

A sequential [3 + 2] cycloaddition and Michael addition reaction of ynones with benzylidenepyrazolones afforded cyclopentanone-fused spiro-pyrazolones catalyzed by DPPB via dual α′,α′-C(sp³)–H bifunctionalization.

Diastereoselective synthesis of cyclopentene spiro-rhodanines containing three contiguous stereocenters via phosphine-catalyzed [3 + 2] cycloaddition or one-pot sequential [3 + 2]/[3 + 2] cycloaddition

5-Spiro-cyclopentene-rhodanine derivatives have been synthesized through two different diastereoselective phosphine-catalyzed cascade reactions in excellent diastereoselectivities and good to excellent yields.

Diastereo- and enantioselective construction of cyclohexanone-fused spirospyrazolones containing four consecutive stereocenters through asymmetric sequential reactions

The diastereo- and enantioselective synthesis of cyclohexanone-fused spirospyrazolones through an asymmetric Michael/Michael/aldol cascade reaction catalyzed by squaramide and diphenylprolinol silyl ether, followed by a sequential oxidation was developed.