Asymmetric Synthesis of Spiropyrazolones by Sequential Organo- and Silver Catalysis

NIS-Promoted Chemodivergent and Diastereoselective Synthesis of Pyrrolinyl and Cyclopentenyl Spiropyrazolones via Regulated Cyclization of Alkylidene Pyrazolones with Enamino Esters

An N-iodosuccinimide-promoted annulation of alkylidene pyrazolones with enamino esters has been explored to construct a spiropyrazolone moiety through a Michael addition/iodination/intramolecular nucleophilic substitution sequence. When the reaction was performed in acetonitrile at 100 °C, it furnished pyrrolinyl spiropyrazolones exclusively in an anti configuration through N-attacking cyclization. When the reaction was performed in dimethyl sulfoxide at 80 °C in the presence of K2HPO4, it afforded cyclopentenyl spiropyrazolones exclusively in the syn configuration through C-attacking cyclization. A plausible mechanism has also been proposed.

Total Synthesis of Penicibilaenes Enabled by a Tandem Double Conia-ene Type Reaction

The total syntheses of penicibilaenes A and B are described. The key step is the tBuOK/DMSO-mediated tandem 5-exo-dig Conia-ene type reaction and 6-exo-dig Conia-ene type reaction to install the tricyclic [6.3.1.01,5] dodecane core of penicibilaenes from dibutynyl cyclohexanone in a single step, together with a sequence of copper-mediated conjugate addition and Crabtree's hydrogenation to forge the stereogenic centers at C5 and C2, respectively.

The Chameleonic Nature of the Nitro Group Applied to a Base-Promoted Cascade Reaction To Afford Indane-Fused Dihydrofurans

We disclose a Michael/Conia-ene/SN2 cascade reaction for the synthesis of Indane-fused dihydrofurans from 1,3-dicarbonyl compounds and 2-alkynylnitrostyrenes promoted by potassium carbonate in DMSO at room temperature. In this reaction, the nitro group has a chameleonic role, first as an electron-withdrawing group for the Michael addition, then the nitronate behaves as a nucleophile, and finally, the allylic nitro acts as a leaving group. The product is obtained as a single diastereomer, affording up to 82% with 1,3-keto esters and 58% with 1,3-diketones. Furthermore, DFT calculations of the reaction mechanism explained the chemoselective addition of the nitronate over the enolate to the unactivated triple bond, with the enolate addition being highly endothermic.

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.

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.

Organo/Silver Dual Catalytic (3 + 2)/Conia-Ene Type Cyclization: Asymmetric Synthesis of Indane-Fused Spirocyclopenteneoxindoles

Developing efficient strategies to synthesize spirocyclopenteneoxindoles is an attractive target due to their potential biological activity. This work described the thiourea/silver dual catalytic (3 + 2)/Conia-ene type reaction of 2-(2-oxoindolin-3-yl)malononitrile with ortho-ethynyl substituted nitrostyrene. The reaction features mild conditions and good atom- and step-economy. Three new C-C bonds were formed within one synthetic step, providing the indane-fused spirocyclopenteneoxindoles in good yields, with excellent chemo-, regio-, and stereoselectivity.

Stereoselective Domino Reactions in the Synthesis of Spiro Compounds

This review summarizes the latest developments in asymmetric domino reactions, with the emphasis on the preparation of spiro compounds. Discussions on the stereoselectivity of the transformations, the reaction mechanisms, the rationalization of the stereochemical outcome, and the applications of domino reactions to the synthesis of biologically active molecules and natural products are included when appropriate.

1 Introduction

2 Asymmetric Domino Reactions

2.1 Domino Reactions Initiated by Michael Reactions

2.2 Domino Reactions Initiated by Mannich Reactions

2.3 Domino Reactions Initiated by Knoevenagel Reactions

2.4 Domino Reactions Initiated by Cycloaddition Reactions

2.5 Domino Reactions Initiated by Metal Insertion

2.6 Other Mechanisms

3 Conclusion

Asymmetric 1,3-dipolar cycloaddition of 4-aminopyrazolone-based azomethine ylides: a straightforward approach to spiropyrazolones

The asymmetric [3+2] cycloaddition of 4-amino pyrazolone-derived azomethine ylides with α,β-enones has been established for the synthesis of 4-spiropyazolones derivatives with four contiguous stereocenters. This cycloaddition process delivered spiro[pyrrolidine-2,4’-pyrazolone] derivatives...

Catalytic asymmetric construction of dispirotriheterocyclic structures through [3+2] cycloadditions of 4-amino pyrazolone-based azomethine ylides

An efficient and convenient catalytic asymmetric [3+2] cycloaddition of 4-amino pyrazolone-based azomethine ylides was developed, which delivers the multi-pharmacophore-containing dispirotriheterocyclic scaffolds with excellent stereoselectivities.

C-4 benzofuranylation of pyrazolones by a metal-free catalyzed indirect heteroarylation strategy

A metal-free catalyzed indirect heteroarylation of pyrazolones with 2-(3-hydroxy-3,3-diarylprop-1-yn-1-yl) phenols has been developed, and a series of novel 4-benzofuranyl substituted pyrazolone derivatives were obtained in moderate to excellent yields (up to 90%). The process has the salient features of metal-free catalysis, operational simplicity, good substrate compatibility and mild reaction conditions. In particular, the integration of the pyrazolone skeleton and benzofuran scaffold into a single molecule is expected to be of potential interest for medicinal research. In addition, the yield and efficiency are basically maintained in the gram-scale experiment, which makes the practical application of the process more prominent.

Experimental and Theoretical DFT Investigations in the [2,3]-Wittig-Type Rearrangement of Propargyl/Allyl-Oxy-Pyrazolones

Here we report the synthesis of interesting 3-alkyl-4-hydroxy-1-aryl-4-(propa-1,2-dienyl)1H-pyrazol-5(4H)-ones and 9-alkyl-7-aryl-1-oxa-7,8-diazaspiro[4.4]nona-3,8-dien-6-ones, starting from 1,2-diaza-1,3-dienes (DDs) and propargyl alcohol. The reaction proceeds through a sequence Michael-type nucleophilic attack/cyclization/[2,3]-Wittig rearrangement. In the same way, the reaction between the aforementioned DDs and allyl alcohol furnished 4-allyl-4-hydroxy-3-alkyl-1-aryl-1H-pyrazol-5(4H)-ones. A DFT study was also carried out, in order to have decisive clarifications about the mechanism.

Enantioselective Synthesis of Spiropyrazolone-Fused Cyclopenta[c]chromen-4-ones Bearing Five Contiguous Stereocenters via (3+2) Cycloaddition

An enantioselective synthesis of spiropyrazolone-fused cyclopenta[c]chromen-4-ones is demonstrated via a (3+2) cycloaddition reaction. The reactions of 3-homoacylcoumarins and α,β-unsaturated pyrazolones in the presence of the cinchona-alkaloid derived hydrogen-bonding catalyst provide aforementioned spiropyrazolone-chromenone adducts bearing five contiguous stereocenters, of which one is the spiro all-carbon quaternary stereocenter in high yields (up to 98%) with good to excellent stereoselectivities (>25:1 dr and up to 99% ee). This one-pot methodology could also be practically demonstrated on a gram-scale with similar efficacy.

Enantioselective Friedel-Crafts reaction of hydroxyarenes with nitroenynes to access chiral heterocycles via sequential catalysis

Naphthols, hydroxyindoles and an activated phenol are reacted with differently substituted (E)-nitrobut-1-en-3-ynes using the commercially available Rawal's chiral squaramide. The corresponding β-nitroalkynes were obtained with good yields and excellent enantioselectivities. Moreover, dihydronaphthofurans can be accessed via silver catalysed cyclization in a tandem one-pot procedure, with high preservation of the optical purity.

Highly Diastereoselective Hydrosilane-Assisted Rhodium-Catalyzed Spiro-Type Cycloisomerization of Succinimide and Pyrazolone-Based Functional 1,6-Dienes

Organosilicon compounds are important reagents and synthetic intermediates that play a key role in the construction of new materials and complex products. Here we show a highly diastereoselective rhodium-catalyzed cycloisomerization of 1,6-dienes, in which the use of (EtO)₃ SiH accelerates the intramolecular cyclization reaction to afford a novel spiro-fused succinimide and pyrazolone derivatives in moderate to excellent yields as a single diastereoisomer. The proposed mechanism involves an active Rh-H species from the hydrosilane that is the H-donor in this spiro-type cycloisomerization reaction.

Enantioselective synthesis of functionalized 1,4-dihydropyrazolo-[4',3':5,6]pyrano[2,3-b]quinolines through ferrocenyl-phosphine-catalyzed annulation of modified MBH carbonates and pyrazolones

An enantioselective synthesis of highly functionalized 1,4-dihydropyrazolo[4',3':5,6]pyrano[2,3-b]quinolines from modified MBH carbonates and pyrazolones via a chiral phosphine-mediated alkylation/annulation sequence has been realized. The chiral dihydropyrano[2,3-c]pyrazoles bearing bio-active condensed heterocycles were facilely formed in good chemical yields and with high to excellent enantioselectivity by utilizing low catalyst loading.

Stretchable chiral pockets for palladium-catalyzed highly chemo- and enantioselective allenylation

Pyrazolones are a vital class of heterocycles possessing various biological properties and much attention is paid to the diversified synthesis of enantiopure pyrazolone derivatives. We describe here the development of diphenylphosphinoalkanoic acid based chiral bisphosphine ligands, which are successfully applied to the palladium-catalyzed asymmetric allenylation of racemic pyrazol-5-ones. The reaction affords C-allenylation products, optically active pyrazol-5-ones bearing an allene unit, in high chemo- and enantioselectivity, with DACH-ZYC-Phos-C1 as the best ligand. The synthetic potential of the C-allenylation products is demonstrated. Furthermore, the enantioselectivity observed with DACH-ZYC-Phos-C1 is rationalized by density functional theory studies.

Chiral pyrazolone derivatives show promising biological activity in commercial drugs. Here, the authors report an enantioselective allenylation of pyrazolones by fine tuning of Trost’s ligands, which leads to a chiral pocket featuring high efficiency and asymmetric induction in the catalytic process.

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).

Highly enantioselective one-pot sequential synthesis of valerolactones and pyrazolones bearing all-carbon quaternary stereocentres

Highly enantiopure and bioactive δ-valerolactones and pyrazolones, bearing α-all-carbon quaternary stereocentres, were successfully and sequentially prepared via a one-pot procedure starting from readily available, inexpensive materials, catalysed by a new chiral squaramide under mild reaction conditions. An organocatalytic Michael reaction afforded the valerolactones, while a one-pot Michael-hydrazinolysis-imidization cascade yielded the pyrazolones. This procedure is economically efficient and environmentally benign.

A three-component, general and practical route for diastereoselective synthesis of aza-spirocyclic pyrazolones via a decarboxylative annulation process

An efficient, general, and practical route for highly diastereoselective synthesis of aza-spirocyclic pyrazolones from easily available α-amino acids, aldehydes, and alkylidene pyrazolones by means of a decarboxylative annulation process is reported.

Catalytic asymmetric construction of C-4 alkenyl substituted pyrazolone derivatives bearing multiple stereoelements

An organocatalytic asymmetric process was reported for the sterically precise construction of C-4 alkenyl substituted pyrazolone derivatives bearing multiple stereoelements.

Enantioselective [3 + 2] annulation of 4-isothiocyanato pyrazolones and alkynyl ketones under organocatalysis

An asymmetric [3 + 2] annulation reaction of 4-isothiocyanato pyrazolones with alkynyl ketones is developed, providing expeditious access to spiro[pyrroline–pyrazolones].

The Use of Domino Reactions for the Synthesis of Chiral Rings

This short review highlights the recent developments reported in the last four years on the asymmetric construction of chiral rings based on enantioselective domino reactions promoted by chiral metal catalysts.

1 Introduction

2 Formation of One Ring Containing One Nitrogen Atom

3 Formation of One Ring Containing One Oxygen/Sulfur Atom

4 Formation of One Ring Containing Several Heterocyclic Atoms

5 Formation of One Carbon Ring

6 Formation of Two Rings

7 Conclusion

Diversity-Oriented Synthesis of Spiropentadiene Pyrazolones and 1H-Oxepino[2,3-c]pyrazoles from Doubly Conjugated Pyrazolones via Intramolecular Wittig Reaction

An efficient method for the diversity-oriented synthesis of spiropentadiene pyrazolones and 1H-oxepino[2,3-c]pyrazoles is reported. The methodology attributes O-acylation of phosphorus zwitterions which were formed by a tandem phospha-1,6-addition of PBu₃ to α,β,γ,δ-unsaturated pyrazolones, further generating betaine intermediates that preferentially resulted in the aforementioned cyclic products in a diversity-oriented manner. The mechanistic investigations revealed that formation of the betaines is the key step to provide the products via an intramolecular Wittig reaction or an unprecedented δ-C-acylation/cyclization/Wittig reaction.

A Rh-catalyzed three-component reaction for the diastereoselective synthesis of pyrazolone derivatives with contiguous quaternary stereocenters

A diastereoselective three-component reaction of diazo compounds with alcohols and pyrazolinone ketimines by utilizing rhodium(ii) catalysis via interception of transient oxonium ylides is reported. The reaction provides an efficient approach for the facile construction of polyfunctionalized pyrazolone derivatives bearing two contiguous quaternary stereocenters in good yields with high regioselectivities and excellent diastereoselectivities.

In(OTf)3-Catalyzed One-Pot Tandem Mannich and Conia-Ene Cyclization Reaction of N-Propargyl Amido Alcohols with 1,3-Dicarbonyl Compounds: An Approach To Construct Tetrahydro-1H-pyrrolo[2,1-a]isoindolone-1,1-dicarboxylate and Its Application

A one-pot tandem reaction has been developed for the synthesis of substituted tetrahydropyrroloisoindolone via Mannich reaction of N-propargyl amido alcohols with 1,3-dicarbonyl compounds followed by Conia-ene cyclization reaction in moderate to good yields catalyzed by indium(III)triflate [In(OTf)₃]. The reaction is highly regioselective with an exo-cyclic double bond in the pyrrolidine ring. The substituted tetrahydropyrroloisoindolone can be converted to 5H-pyrrolo[2,1-a]isoindol-5-one via decarboxylative aromatization reaction.

Tandem Carbenoid C-H Functionalization/Conia-ene Cyclization of N-Propargyl Indoles Generates Pyrroloindoles under Cooperative Rh(II)/Zn(II) Catalysis

The decomposition of diazodicarbonyl compounds in the presence of various metal catalysts has become a reliable method for the functionalization of indoles via carbenoid intermediates. Exploiting the nucleophilic reactivity of the in situ generated malonic ester product formed, we herein report a tandem C-H functionalization/Conia-ene cyclization of N-alkyne tethered indoles. This double functionalization of diazodicarbonyls generates a range of pyrrolo[1,2-a]-, pyrido[1,2-a]-, and azepino[1,2-a]indole products with good synthetic efficiency.

Enantioselective construction of dispirotriheterocycles featuring a 4-aminopyrazolone motif through a cascade Michael/cyclization process

A highly asymmetric approach to multicyclic dispiro [pyrazolone-pyrrolidinethione-oxindole] core structures bearing three contiguous stereogenic centers through a cascade Michael addition/cyclization reaction of 4-isothiocyanato pyrazolones with 3-ylideneoxindoles was developed.

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.

Squaramide-catalyzed asymmetric Mannich reactions between 3-fluorooxindoles and pyrazolinone ketimines

An enantioselective Mannich reaction between 3-fluorooxindoles and pyrazolinone ketimines has been developed for the construction of amino-pyrazolone-oxindoles containing stereogenic C-F units. Based on this new protocol that allows for the generation of two adjacent tetrasubstituted stereocenters, a variety of structurally diverse fluorinated amino-pyrazolone-oxindoles were obtained in good to excellent yields with excellent diastereoselectivities and enantioselectivities (up to 98% yield, >20 : 1 dr and >99% ee). What's more, good yield and high stereoselectivities were obtained in the gram-scale reaction.

Proline bulky substituents consecutively act as steric hindrances and directing groups in a Michael/Conia-ene cascade reaction under synergistic catalysis

In this study, we report a highly stereoselective and versatile synthesis of spiro pyrazolones, promising motifs that are being employed as pharmacophores. The new synthetic strategy merges organocatalysis and metal catalysis to create a synergistic catalysis using proline derivatives and Pd catalysts. This protocol is suitable for late-stage functionalization, which is very important in drug discovery. Additionally, a thorough computational study proved to be very useful to elucidate the function of the different catalysts along the reaction, showing a peculiar feature: the -CPh2OSiMe3 group of the proline catalyst switches its role during the reaction. In the initial Michael reaction, this group plays its commonly-assumed role of bulky blocking group, but the same group generates π-Pd interactions and acts as a directing group in the subsequent Pd-catalyzed Conia-ene reaction. This finding might be very relevant especially for processes with many steps, such as cascade reactions, in which functional groups are assumed to play the same role during all reaction steps.

Organocatalytic asymmetric [4 + 1] annulation of in situ generated ortho-quinomethanes with 4-halo pyrazolones: straightforward access to chiral spiro-benzofuran pyrazolones

Asymmetric [4 + 1] annulation of ortho-quinomethanes with 4-halo pyrazolones was developed to construct spiro-benzofuran pyrazolones.

Metal-free tandem reaction synthesis of spiro-cyclopropyl fused pyrazolin-5-one derivatives

A highly efficient cascade annulation approach was developed for the synthesis of novel spiro-cyclopropyl fused pyrazolin-5-ones from pyrazole-3-ketone substrates and two-component sulfur ylides in an acidic environment.