Substrate-directed divergent annulations of sulfur ylides: synthesis of functionalized bispirocyclopentane and bispirocyclopropane derivatives

Herein, an efficient, substrate-directed divergent [2 + 3]/[2 + 1] annulation of tetra-substituted oxa-dienes and allylic sulfur ylides has been successfully developed. Under precise annulation regulation, a series of functionalized bispirocyclopentane and bispirocyclopropane derivatives were synthesized in a highly stereoselective and economical manner (up to 95% yield, >20 : 1 dr or >20 : 1 E/Z). This protocol offers the advantages of mild conditions, high chemo-, regio- and diastereoselectivity and broad substrate compatibility. In addition, the synthetic practicality of this protocol was evaluated through a scale-up preparation and a series of three-component reactions utilizing in situ generated sulfur ylides.

Parallel Synthesis of Pyrazolone-Fused Cinnolines by the Palladium-Catalyzed [4 + 2] Annulation of Pyrazol-3-ones with Substituted Allenoates

The synthesis of pyrazolone-fused cinnolines from pyrazol-3-ones and α,γ-substituted allenoates via a palladium-catalyzed C-H activation/annulation cascade was developed. Mechanistic studies revealed the course of the reaction. Initially, N-acyl-valine ligand-assisted ortho-C-H activation gives ortho-alkenylated intermediate. Subsequent cyclopalladation and migratory insertion of allenoate give a seven-membered palladacycle. Reductive elimination finally furnishes pyrazolone-fused cinnolines.

Synthesis of functionalized tetrahydrodibenzo[b,g][1,8]naphthyridin-1(2H)-ones through base-promoted annulation of quinoline-derived dipolarophiles and cyclic enaminones

An eco-friendly and metal-free method for the synthesis of tetrahydrodibenzo[b,g][1,8]naphthyridin-1(2H)-ones was established. Quinoline-derived dipolarophiles and cyclic enaminones as starting materials undergo a 1,4-Michael addition/SNAr tandem annulation reaction affording the target products. This approach features transition metal-free conditions, good functional group tolerance and operational simplicity.

Highly Regio- and Diastereoselective Phosphine-Catalyzed [2 + 4] Annulation of Benzofuran-Derived Azadienes with Allyl Carbonates: Access to Spiro[benzofuran-cyclohexanes]

A novel highly regio- and diastereoselective phosphine-catalyzed [2 + 4] annulation of benzofuran-derived azadienes (BDAs) with acidic hydrogen-tethered allyl carbonates has been developed ingeniously. A range of functionalized spiro[benzofuran-cyclohexane] derivatives with two consecutive stereocenters were smoothly obtained in moderate to excellent yields under mild reaction conditions from readily available materials. Moreover, this method is a practical and scalable strategy that creates the core structural motif of the fungistatic drug, griseofulvin.

An interrupted Corey-Chaykovsky reaction of designed azaarenium salts: synthesis of complex polycyclic spiro- and fused cyclopropanoids

Simultaneous dearomatizing spirannulation of pyridinium salts is still in its infancy. Here, we present an organized skeletal remodeling of designed pyridinium salts by utilizing an interrupted Corey-Chaykovsky reaction to access unprecedented and structurally intriguing molecular architectures such as the vicinal bis-spirocyclic indanones and spirannulated benzocycloheptanones. This hybrid strategy rationally merges the nucleophilic features of sulfur ylides with the electrophilic pyridinium salts to achieve the regio- and stereoselective synthesis of new classes of cyclopropanoids. The plausible mechanistic pathways were derived from experimental results and control experiments.

Asymmetric synthesis of the perhydroepoxyethanoindole core via sequential [4 + 2]-addition/reduction/fluoroannulation reactions

Herein, we present the sequential aminocatalytic [4 + 2]-addition/reduction and fluoroannulation reactions to afford a novel class of bridged fluoro-perhydroepoxyethanoindole spiropyrazolone and fluoro-perhydroepoxyethanoindole spirooxindole moieties with six contiguous stereocenters. An array of perhydroepoxyethanoindole core derivatives (up to 31 examples) mimicking aspidosperma alkaloids were obtained with moderate to good yields and excellent enantio- and diastereo-selectivities (up to 69% overall yield, up to 99.9% ee and up to >20 : 1 dr). Furthermore, we have also disclosed the synthesis of the unexpected tribromo derivative of hexahydroepoxyethanoindole spiropyrazolone in a moderate yield with excellent selectivity by employing the developed protocol in sequential bromoannulation reactions.

Advanced Application of Planar Chiral Heterocyclic Ferrocenes

This manuscript is reviewing the superior catalytic activity and selectivity of ferrocene ligands in a wide range of reactions: reduction of ketones, hydrogenation of olefins, hydroboration, cycloaddition, enantioselective synthesis of biaryls, Tsuji–Trost allylation. Moreover, the correlation between a ligand structure and its catalytic activity is discussed in this review.

[3 + 2] vs. [4 + 1] Annulation: revisiting mechanism studies on the phosphine-catalysed domino sequence of alkynoates and activated methylenes

The mechanism of the phosphine-catalysed domino sequence of alkynoates and activated methylenes has been computationally studied. The computational results revealed that the [3 + 2] annulation sequence could be ruled out, due to a difficult Knoevenagel condensation of aromatic aldehydes and active methylenes. The reaction proceeds through a [4 + 1] annulation pathway, which involves a phosphine-catalysed MBH-type reaction followed by a [1,5]-proton shift and dehydration to afford vinyl phosphonium intermediates as four-carbon synthons in the annulation reaction. Then 1,3-dicarbonyls act as nucleophiles to attack vinyl phosphonium intermediates, subsequently leading to a stepwise [1,3]-proton shift and an intramolecular nucleophilic attack to close the five-member ring.

Al-Hussain S, E. A. Zaki M, H. Asghar B, A. Muhammad Z. Synthesis of spiropyrazoles under organic and nonorganic catalysis

Abstract:

Spiropyrazoles display many biological biological activities such as antitumor, vasodilation, analgesic, phosphodiesterase inhibitors, aldosterone antagonistic, anabolic, androgenic, anti-inflammatory, progestational and salt-retaining activities and they also exert neuroprotection in dopaminergic cell death. Many efforts have been made to obtain these derivatives with high yield and excellent regio-, diastereo- and enantioselectivities. Most of the spiroprazole synthesis methods were proceeded in good to excellent yield in the presence of organic catalysts as for examples squaramide, NHC pre-catalyst, pyrrole derivatives, bis-oxazoline, DMAP, DABCO, thiourea derivatives, DBU, acetic acid and quinoline catalysts. In addition, the inorganic and organo-metallic catalysts have been proven their efficiency in synthesis of various types of spiro-pyrazoles in excellent yield. Thus, in this review we have compiled all citations for the synthesis of spiropyrazoles in the presence of various types of catalysts such as organic, inorganic, and metalorganic catalysts in the range 2020 to 2012. This review article is a useful compilation for researchers interested in the synthesis of spiropyrazole derivatives and will assist them in selecting appropriate catalysts for preparation of their spiropyrazoles.

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.

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.

Recent advances in the applications of pyrazolone derivatives in enantioselective synthesis

Pyrazolones and pyrazoles, featuring nitrogen-nitrogen bonds, are two of the most important classes of heterocycles, owing to their widespread occurrence in medicinal chemistry and functional materials. The last decade has witnessed a rapid increase in the construction of chiral pyrazolone and pyrazole derivatives, with the application of pyrazolone derivatives as powerful synthons. Since our last review in 2018, a large number of new achievements has emerged in this area, requiring a timely update. Thus, this review summarizes these elegant achievements based on the multiple reactive sites of different pyrazolone synthons. In addition, important mechanisms and interesting biological investigations relating to the corresponding products are also discussed.

Organocatalytic Regio- and Enantioselective [3 + 2]-Annulations of Ninhydrin-Derived Morita-Baylis-Hillman Carbonates with 3-Methyleneoxindoles

A type of Morita-Baylis-Hillman (MBH) carbonates has been developed from ninhydrin. These MBH carbonates have been successfully employed as 3C-synthons in the organocatalytic asymmetric [3 + 2]-annulations of the isatin-derived electron-deficient olefins, affording structurally diverse spirooxindoles in high yield with excellent stereoselectivity. In particular, the regioselectivity of MBH carbonates was controlled by the reaction partner, 3-methyleneoxindoles with carbonyl groups (R = ArCO), affording β-selective products and 3-methyleneoxindoles with ester groups (R = CO₂Me) furnishing γ-selective products. The representative scale-up reactions and transformation of product were examined. The reaction mechanism was expounded by control experiments.

[3+2] regioselective annulation reaction of 2-arylidene-1,3-indandiones towards synthesis of spirocyclopentenes: understanding the mechanism of γ-attack vs. α-attack using DFT studies

A regioselective [3+2] cyclisation reaction between 2-arylidene-1,3-indanedione and ethyl 2,3-butadienoate catalysed by triphenylphosphine has been demonstrated to synthesize functionalised spirocyclic cyclopentenes. The reaction tolerated various electron-rich and electron-deficient aryl substituted 2-arylidene-1,3-indanediones with high to excellent chemical yields (up to 99%) and moderate to good regioselectivity (up to 5 : 1). DFT studies have also been carried out to understand the regioselective nature of this reaction. The results of Frontier molecular orbital calculations and the activation energy (E_a) favour the formation of compound 3avia γ-attack compared to that of 4avia α-attack.

A [3+2] annulation protocol for the construction of functionalized spirocyclopentenes utilizing 1,3-indanedione derived benzylidene-1,3-indanedione and ethyl-2,3-butadienoate at room temperature was developed.

An update on the progress of cycloaddition reactions of 3-methyleneindolinones in the past decade: versatile approaches to spirooxindoles

Cycloaddition reactions are of great interest due to their potential and rapid construction of optically enriched spiro-cyclic products. 3-Methyleneindolinones have been proven to be a valuable precursor in cycloaddition reactions for the construction of diverse 3,3'-spirocyclic oxindoles. Their versatile reactivity has provided a new forum for the development of a variety of building blocks and synthetic compounds, including bioactive molecules. Herein, significant accomplishments in the cycloaddition reactions of 3-methyleneindolinones for the synthesis of spirooxindoles have been summarised and elaborated. The review is outlined according to the type of cycloaddition such as [2 + 1], [2 + 2], [3 + 2], [4 + 2] and [5 + 2] cycloaddition reactions.

Enantioselective Phosphine-Catalyzed Trimerization of γ-Aryl-3-butynoates via Isomerization/[3 + 2] Cyclization/Michael Addition Cascade

We disclose an l-isoleucine-derived amide phosphine-catalyzed trimerization of γ-aryl-3-butynoates, which undergo an isomerization to allenoate, [3 + 2] cyclization, and Michael addition cascade. Exocyclopentene derivatives bearing an all-carbon quaternary stereocenter were constructed stereospecifically and enantioselectively. A wide variety of γ-aryl-3-butynoates could be employed to deliver optically pure cyclopentene derivatives in moderate to good yields with ee values of ≥95% and in most cases ≥98%.

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.

Phosphorus-Based Catalysis

Phosphorus-based organocatalysis encompasses several subfields that have undergone rapid growth in recent years. This Outlook gives an overview of its various aspects. In particular, we highlight key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organophosphorus compound-mediated single electron transfer processes. We briefly summarize five additional topics: chiral phosphoric acid catalysis, phosphine oxide Lewis base catalysis, iminophosphorane super base catalysis, phosphonium salt phase transfer catalysis, and frustrated Lewis pair catalysis. Although it is not catalytic in nature, we also discuss novel discoveries that are emerging in phosphorus(V) ligand coupling. We conclude with some ideas about the future of organophosphorus catalysis.

Organocatalytic enantioselective [2 + 4]-annulation of γ-substituted allenoates with N-acyldiazenes for the synthesis of optically active 1,3,4-oxadiazines

An enantioselective [2 + 4]-annulation of γ-substituted allenoates with N-acyldiazenes has been developed for the first time. In the presence of an l-proline-derived DMAP analogue, the annulation proceeded smoothly to afford a broad range of 1,3,4-oxadiazine derivatives in good to excellent yields with high stereoselectivities.

Recent Advances in Catalytic Enantioselective Synthesis of Pyrazolones with a Tetrasubstituted Stereogenic Center at the 4-Position

Pyrazolone [2,4-dihydro-3H-pyrazol-4-one] represents one of the most important five-membered nitrogen heterocycles which is present in numerous pharmaceutical drugs and molecules with biological activity. Recently, many catalytic methodologies for the asymmetric synthesis of chiral pyrazolones have been established with great success, specially, for the synthesis of pyrazolones bearing a tetrasubstituted stereocenter at C-4. This review summarizes these excellent research studies since 2018, including representative examples and some mechanistic pathways explaining the observed stereochemistry.

1 Introduction

2 Catalytic Enantioselective Synthesis of Chiral Pyrazolones with a Full Carbon Tetrasubstituted Stereocenter at C-4

3 Catalytic Enantioselective Synthesis of Chiral Pyrazolones with a Quaternary Carbon Stereocenter at C-4 bearing a Heteroatom

4 Catalytic Enantioselective Synthesis of Chiral Spiropyrazolones

5 Conclusion

Phosphine catalyzed [3+2] cyclization/Michael addition of allenoate with CS2 to form 2-thineyl vinyl sulfide

We have developed a DPPE-catalyzed three molecular two component tandem reaction of γ-substituted allenoate and CS2 to construct 2-thineyl vinyl sulfide through phosphine catalyzed [3+2] cyclization followed by Michael addition. The synthetic value of the 2-thineyl vinyl sulfide was demonstrated by a concise synthesis of an anti-glaucoma agent.

Enantioselective dearomative [3 + 2] annulation of 3-hydroxy chromanones with azonaphthalenes

Enantioselective dearomative [3 + 2] annulation of 3-hydroxy chromanones with azonaphthalenes provided a large variety of chromanone fused indolines in moderate to good yields with generally good enantioselectivities.

Recent developments in the synthesis and applications of chiral ferrocene ligands and organocatalysts in asymmetric catalysis

This review highlights recent advances in the synthesis and application of ferrocene-containing chiral ligands and organocatalysts in asymmetric catalysis.