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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (30 June 2018) | Viewed by 82159

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Prof. Dr. László Somsák

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Department of Organic Chemistry, University of Debrecen, P.O. Box 400, H-4002 Debrecen, Hungary
Interests: organic synthesis; carbohydrates; c-glycosyl derivatives; anomeric spirocycles; lectine antagonists; glycoenzyme inhibitors
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Anthony J. Burke

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Department of Chemistry and Centro de Química de Évora, Institute for Research and Advanced Training and School of Science and Technology, University of Évora Colégio Luís Verney, Rua Romão Ramalho, 59, 7000 Évora, Portugal
Interests: medicinal chemistry; drug design; organic synthesis; catalysis; organocatalysis; transition metal catalyzed reactions; small molecule synthesis; optoelectronic materials; mechanism elucidation; polymer synthesis; NMR
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Spiro compounds (also named as spiranes following the suggestion of Adolf von Baeyer as early as 1900) are ubiquitous molecules, which contain a fused bicyclic system that share a single atom. A search for the key term “spiro” in the SciFinder database at the beginning of April 2017 resulted in more than 147,000 hits including 5000–6000 publications per annum after 2010. This enormous research activity encompasses a large number of fields in chemistry (especially organic and medicinal chemistry—with an emphasis on heterocyclic systems), but also includes pharmacology, crystallography, materials science, physics, biochemistry, molecular biology, engineering, energy and fuels, just to mention the most active areas. The immense interest in spirocycles, besides their unique features related to isolation from natural sources, synthesis and stereochemistry, is fuelled by an extremely wide range of useful properties, that comprise among others anti-cancer, antibacterial, antifungal, anti-diabetic, anti-HIV, cytotoxic, diuretic, spasmolytic, antiphlogistic, anti-hypertensive, anti-depressant, anxiolytic, anti-fouling, anti-feedant, herbicidal, plant growth regulatory effects; photochromism; and hole-transporting ability.

These properties have been translated into several practical applications which include marketed drugs; ophtalmic lenses and sunscreening (for instance in sunglasses); auxiliary compounds in stereoselective syntheses; electronic displays and optical data storage devices, etc. In addition, many other utilizations, such as new medications, chemical biosensing, controlled release drug delivery, molecular switches, and solar cells, are in a developmental phase.

With regard to pharmaceutical applications, it should also be mentioned that at the current time, driven by the ever-increasing pace of drug discovery, medicinal chemists are turning to new unexplored regions of chemical space in the quest to find more potent medicines. Thus, unusual strained spirocyclic bioisosteres are important targets, as they show diverse new biological activities. Moreover, besides potentially modulating binding potency and specificity, spirocyclic scaffolds may also improve bioavailability and metabolic stability, key issues when developing new pharmacological entities.

This forthcoming Special Issue of Molecules entitled “Advances in Spiro Compounds“ will be devoted to this amazing class of compounds, covering recent key findings in any of the above research fields.

Prof. Dr. László Somsák
Prof. Dr. Anthony J. Burke
Guest Editors

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Keywords

spiro compounds
isolation
molecular design
synthesis
medicinal chemistry
biological activity
drugs
inhibition
conformational restriction
photochromism
polymers
applications

Published Papers (14 papers)

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22 pages, 5709 KiB

Open AccessFeature PaperArticle

Unsymmetrical Spiroalkanedithiols Having Mixed Fluorinated and Alkyl Tailgroups of Varying Length: Film Structure and Interfacial Properties

by Pawilai Chinwangso, Lydia R. St. Hill, Maria D. Marquez and T. Randall Lee

Molecules 2018, 23(10), 2632; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23102632 - 13 Oct 2018

Cited by 12 | Viewed by 3629

Abstract

A custom-designed series of unsymmetrical spiroalkanedithiols having tailgroups comprised of a terminally fluorinated chain and a hydrocarbon chain of varying lengths were synthesized and used to prepare self-assembled monolayers (SAMs) on gold substrates. The specific structure of the adsorbates was of the form [CH₃(CH₂)_n][CF₃(CF₂)₇(CH₂)₈]C[CH₂SH]₂, where n = 7, 9, and 15 (designated as F8H10-C10, F8H10-C12, and F8H10-C18, respectively). The influence of the length of the hydrocarbon chain in the bidentate dithiol on the structure and interfacial properties of the monolayer was explored. A structurally analogous partially fluorinated monodentate alkanethiol and the corresponding normal alkanethiols were used to generate appropriate SAMs as reference systems. Measurements of ellipsometric thickness showed an unexpectedly low film thickness for the SAMs derived from the bidentate adsorbates, possibly due to disruptions in interchain packing caused by the fluorocarbon chains (i.e., phase-incompatible fluorocarbon-hydrocarbon interactions), ultimately giving rise to loosely packed and disordered films. Analysis by X-ray photoelectron spectroscopy (XPS) were also consistent with a model in which the films were loosely packed; additionally, the XPS spectra confirmed the attachment of the sulfur headgroups of the bidentate adsorbates onto the gold substrates. Studies of the SAMs by polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) suggested that as the length of the hydrocarbon chain in the adsorbates was extended, a more ordered surface was achieved by reducing the tilt of the fluorocarbon segment. The wettability data indicated that the adsorbates with longer alkyl chains were less wettable than those with shorter alkyl chains, likely due to an increase in interchain van der Waals forces in the former. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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11 pages, 4063 KiB

Open AccessArticle

Utilizing a Spiro Core with Acridine- and Phenothiazine-Based New Hole Transporting Materials for Highly Efficient Green Phosphorescent Organic Light-Emitting Diodes

by Ramanaskanda Braveenth, Il-Ji Bae, Ji-Hun Han, Wu Qiong, Guk Seon, Kanthasamy Raagulan, Kihun Yang, Young Hee Park, Miyoung Kim and Kyu Yun Chai

Molecules 2018, 23(4), 713; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23040713 - 21 Mar 2018

Cited by 9 | Viewed by 4592

Abstract

Two new hole transporting materials, 2,7-bis(9,9-diphenylacridin-10(9H)-yl)-9,9′ spirobi[fluorene] (SP1) and 2,7-di(10H-phenothiazin-10-yl)-9,9′-spirobi[fluorene] (SP2), were designed and synthesized by using the Buchwald–Hartwig coupling reaction with a high yield percentage of over 84%. Both of the materials exhibited high glass transition temperatures of over 150 °C. In order to understand the device performances, we have fabricated green phosphorescent organic light-emitting diodes (PhOLEDs) with SP1 and SP2 as hole transporting materials. Both of the materials revealed improved device properties, in particular, the SP2-based device showed excellent power (34.47 lm/W) and current (38.41 cd/A) efficiencies when compare with the 4,4′-bis(N-phenyl-1-naphthylamino)biphenyl (NPB)-based reference device (30.33 lm/W and 32.83 cd/A). The external quantum efficiency (EQE) of SP2 was 13.43%, which was higher than SP1 (13.27%) and the reference material (11.45%) with a similar device structure. The SP2 hole transporting material provides an effective charge transporting path from anode to emission layer, which is explained by the device efficiencies. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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13 pages, 2130 KiB

Open AccessArticle

A Facile One-Pot Construction of Succinimide-Fused Spiro[Pyrrolidine-2,3′-Oxindoles] via 1,3-Dipolar Cycloaddition Involving 3-Amino Oxindoles and Maleimides

by Lunqiang Jin and Feng Liang

Molecules 2018, 23(3), 582; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23030582 - 05 Mar 2018

Cited by 4 | Viewed by 3652

Abstract

Increasing interests have been invested in the development of synthetic strategies toward the construction of spiro[pyrrolidine-2,3′-oxindole], which is the core structural skeleton in some compounds with diverse biological activities. In this work, an efficient diastereoselective 1,3-dipolar cycloaddition reaction of azomethine ylides generated in situ from 3-amino oxindoles and aldehydes with maleimides has been described. The protocol provides a facile and efficient access to structurally diverse succinimide-fused spiro[pyrrolidine-2,3′-oxindole] compounds in good to high yields (up to 93%) with moderate to excellent diastereoselectivities (up to >95:5). The relative stereochemistry of cycloaddition products has been assigned by X-ray diffraction analysis. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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9459 KiB

Open AccessFeature PaperArticle

Spiro[pyrrolidine-3,3′-oxindoles] and Their Indoline Analogues as New 5-HT6 Receptor Chemotypes

by Ádám A. Kelemen, Grzegorz Satala, Andrzej J. Bojarski and György M. Keserű

Molecules 2017, 22(12), 2221; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22122221 - 14 Dec 2017

Cited by 16 | Viewed by 6595

Abstract

Synthetic derivatives of spiro[pyrrolidinyl-3,3′-oxindole] alkaloids (coerulescine analogues) were investigated as new ligands for aminergic G-protein coupled receptors (GPCRs). The chemical starting point 2′-phenylspiro[indoline-3,3′-pyrrolidin]-2-one scaffold was identified by virtual fragment screening utilizing ligand- and structure based methods. As a part of the hit-to-lead optimization a structure-activity relationship analysis was performed to explore the differently substituted 2′-phenyl-derivatives, introducing the phenylsulphonyl pharmacophore and examining the corresponding reduced spiro[pyrrolidine-3,3′-indoline] scaffold. The optimization process led to ligands with submicromolar affinities towards the 5-HT₆ receptor that might serve as viable leads for further optimization. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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2029 KiB

Open AccessArticle

A Diastereoselective Synthesis of Dispiro[oxindole-cyclohexanone]pyrrolidines by 1,3-Dipolar Cycloaddition

by Alexander Anis’kov, Irina Klochkova, Roman Tumskiy and Alevtina Yegorova

Molecules 2017, 22(12), 2134; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22122134 - 04 Dec 2017

Cited by 4 | Viewed by 4898

Abstract

For the first time, arylmethylidene cyclohexanones that are non-symmetrical due to the presence of peripheral substituents were studied in 1,3-dipolar cycloaddition reactions. It is shown that the interaction with the azomethine ylide generated from sarcosine proceeds regio- and diastereoselectively, with the participation of two non-equivalent parts of the dipolarophile. Also for the first time, β-amino ketones (Mannich bases) were used as dipolarophile equivalents of unsaturated ketones. It was found that cycloaddition occurs diastereoselectively at the generated center. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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1434 KiB

Open AccessArticle

Organocatalytic Access to Enantioenriched Spirooxindole-Based 4-Methyleneazetidines

by Giulia Rainoldi, Matteo Faltracco, Claudia Spatti, Alessandra Silvani and Giordano Lesma

Molecules 2017, 22(11), 2016; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22112016 - 21 Nov 2017

Cited by 11 | Viewed by 4026

Abstract

This work describes the synthesis of enantioenriched spiro compounds, incorporating the azetidine and the oxindole motifs. The preparation relies on a formal [2 + 2] annulation reaction of isatin-derived N-tert-butylsulfonyl ketimines with allenoates. The asymmetric induction is secured by an organocatalytic strategy, exploiting a bifunctional cinchona-type β-isocupridine-based catalyst. Some post-transformation products, including unexpected spiropyrroline and 3,3-disubstituted oxindole derivatives, are also presented. Full article

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4388 KiB

Open AccessArticle

9,10-Dihydrophenanthrene with Two Spiro(dibenzocycloheptatriene) Units: A Highly Strained Caged Hydrocarbon Exhibiting Reversible Electrochromic Behavior

by Yusuke Ishigaki, Yuki Hayashi, Kazuma Sugawara, Takuya Shimajiri, Wataru Nojo, Ryo Katoono and Takanori Suzuki

Molecules 2017, 22(11), 1900; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22111900 - 04 Nov 2017

Cited by 12 | Viewed by 6219

Abstract

The title dispiro hydrocarbon 1 was designed as a new electrochromic material. This multiply clamped hexaphenylethane-type electron donor was prepared from 2,2’-diiodobiphenyl via biphenyl-2,2’-diylbis(dibenzotropylium) 2²⁺ salt. X-ray analysis of 1 revealed a highly strained structure as reflected by an elongated “ethane” bond [bond length: 1.6665(17) Å] and nearly eclipsed conformation. The weakened bond was cleaved upon two-electron oxidation to regenerate the deeply colored dication 2²⁺. The reversible interconversion between 1 and 2²⁺ is accompanied not only by a drastic color change but also by C–C bond formation/cleavage. Thus, the voltammogram showed a pair of well-separated redox waves, which is characteristic of “dynamic redox (dyrex)” behavior. The tetrahydro derivative of 1 with two units of spiro(dibenzocycloheptadiene), which suffers from more severe steric congestion, was also prepared. The crystallographically determined bond length for the central C–C bond [1.705(4) Å] is greatest among the values reported for 9,9,10,10-tetraaryl-9,10-dihydrophenanthrene derivatives. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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5021 KiB

Open AccessFeature PaperArticle

Fluorescent “Turn-Off” Detection of Fluoride and Cyanide Ions Using Zwitterionic Spirocyclic Meisenheimer Compounds

by Marina Benet, Marc Villabona, Carles Llavina, Silvia Mena, Jordi Hernando, Rabih O. Al-Kaysi and Gonzalo Guirado

Molecules 2017, 22(11), 1842; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22111842 - 27 Oct 2017

Cited by 12 | Viewed by 5343

Abstract

Stable zwitterionic spirocyclic Meisenheimer compounds were synthesized using a one-step reaction between picric acid and diisopropyl (ZW1) or dicyclohexyl (ZW3) carbodiimide. A solution of these compounds displays intense orange fluorescence upon UV or visible light excitation, which can be quenched or “turned-off” by adding a mole equivalent amount of F⁻ or CN⁻ ions in acetonitrile. Fluorescence is not quenched in the presence of other ions such as Cl⁻, Br⁻, I⁻, NO₂⁻, NO₃⁻, or H₂PO₄⁻. These compounds can therefore be utilized as practical colorimetric and fluorescent probes for monitoring the presence of F⁻ or CN⁻ anions. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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2238 KiB

Open AccessFeature PaperArticle

Glucopyranosylidene-Spiro-Thiazolinones: Synthetic Studies and Determination of Absolute Configuration by TDDFT-ECD Calculations

by Katalin E. Szabó, Sándor Kun, Attila Mándi, Tibor Kurtán and László Somsák

Molecules 2017, 22(10), 1760; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22101760 - 19 Oct 2017

Cited by 6 | Viewed by 4562

Abstract

Reactions of O-peracylated C-(1-bromo-β-d-glucopyranosyl)formamides with thioamides furnished the corresponding glucopyranosylidene-spiro-thiazolin-4-one. While O-debenzoylations under a variety of conditions resulted in decomposition, during O-deacetylations the addition of MeOH to the thiazolinone moiety was observed, and with EtOH and water similar adducts were isolated or detected. The structure and stereochemistry of the new compounds were established by means of NMR and electronic circular dichroism (ECD) data supported by time-dependent density functional theory ECD (TDDFT-ECD) calculations. TDDFT-ECD calculations could efficiently distinguish the proposed epimeric products having different absolute configuration in the spiro heterocyclic ring. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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5292 KiB

Open AccessArticle

Spiropyran-Isoquinoline Dyad as a Dual Chemosensor for Co(II) and In(III) Detection

by Yong-Min Kho and Eun Ju Shin

Molecules 2017, 22(9), 1569; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22091569 - 19 Sep 2017

Cited by 24 | Viewed by 5927

Abstract

Spiropyran derivatives have been studied as light-regulated chemosensors for a variety of metal cations and anions, but there is little research on chemosensors that simultaneously detect multiple metal cations. In this study, a spiropyran derivative with isoquinoline, SP-IQ, was prepared and it functions investigated as a light-regulated sensor for both Co²⁺ and In³⁺ cations. A colorless nonfluorescent SP-IQ converts to a pink-colored fluorescent MC-IQ by UV irradiation or standing in the dark, and MC-IQ returns to SP-IQ with visible light. Upon UV irradiation with the Co²⁺ cation for 7 min, the stronger absorption at 540 nm and the similar fluorescence intensity at 640 nm are observed, compared to when no metal cation is added, due to the formation of a Co²⁺ complex with pink color and pink fluorescence. When placed in the dark with the In³⁺ cation for 7 h, the colorless solution of SP-IQ changes to the In³⁺ complex with yellow color and pink fluorescence, which shows strong absorption at 410 nm and strong fluorescence at 640 nm. Selective detection of the Co²⁺ cation with UV irradiation and the In³⁺ cation in the dark could be possible with SP-IQ by both absorption and fluorescence spectroscopy or by the naked eye. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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570 KiB

Open AccessArticle

An Efficient Synthesis of Spiro[indoline-3,9′-xanthene]trione Derivatives Catalyzed by Magnesium Perchlorate

by Chunfeng Chen, Chunlei Lv, Jianfeng Liang, Jianqing Jin, Lijun Wang, Chunlei Wu and Runpu Shen

Molecules 2017, 22(8), 1295; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22081295 - 04 Aug 2017

Cited by 13 | Viewed by 4642

Abstract

A simple and efficient method for the synthesis of spiro[indoline-3,9′-xanthene]trione derivatives by means of condensation between isatins and 1,3-cyclohexanedione in the presence of a catalytic amount of magnesium perchlorate at 80 °C in 50% aqueous ethanol medium has been described. Notably, the present [...] Read more.

(This article belongs to the Special Issue Advances in Spiro Compounds)

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Review

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3157 KiB

Open AccessReview

Advances in Spiropyrans/Spirooxazines and Applications Based on Fluorescence Resonance Energy Transfer (FRET) with Fluorescent Materials

by Hongyan Xia, Kang Xie and Gang Zou

Molecules 2017, 22(12), 2236; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22122236 - 18 Dec 2017

Cited by 54 | Viewed by 10598

Abstract

Studies on the following were reviewed: (1) the structure of spiropyrans and spirooxazines (two kinds of spiro compounds) under external stimuli and (2) the construction and applications of composite systems based on fluorescence resonance energy transfer (FRET) with fluorescent materials. When treated with different stimuli (light, acids and bases, solvents, metal ions, temperature, redox potential, and so on), spiropyrans/spirooxazines undergo transformations between the ring-closed form (SP), the ring-opened merocyanine (MC) form, and the protonated ring-opened form (MCH). This is due to the breakage of the spiro C–O bond and the protonation of MC, along with a color change. Various novel, multifunctional materials based on photochromic spiropyrans and spirooxazines have been successfully developed because of the vastly differently physiochemical properties posssed by the SP, MC and MCH forms. Among the three different structural forms, the MC form has been studied most extensively. The MC form not only gives complexes with various inorganic particles, biological molecules, and organic chemicals but also acts as the energy acceptor (of energy from fluorescent molecules) during energy transfer processes that take place under proper conditions. Furthermore, spiropyran and spirooxazine compounds exhibit reversible physicochemical property changes under proper stimuli; this provides more advantages compared with other photochromic compounds. Additionally, the molecular structures of spiropyrans and spirooxazines can be easily modified and extended, so better compounds can be obtained to expand the scope of already known applications. Described in detail are: (1) the structural properties of spiropyrans and spirooxazines and related photochromic mechanisms; (2) composite systems based on spiropyrans and spirooxazines, and (3) fluorescent materials which have potential applications in sensing, probing, and a variety of optical elements. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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9931 KiB

Open AccessFeature PaperReview

Synthesis of Spironucleosides: Past and Future Perspectives

by Raquel G. Soengas, Gustavo Da Silva and Juan Carlos Estévez

Molecules 2017, 22(11), 2028; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22112028 - 22 Nov 2017

Cited by 16 | Viewed by 7014

Abstract

Spironucleosides are a type of conformationally restricted nucleoside analogs in which the anomeric carbon belongs simultaneously to the sugar moiety and to the base unit. This locks the nucleic base in a specific orientation around the N-glycosidic bond, imposing restrictions on the flexibility of the sugar moiety. Anomeric spiro-functionalized nucleosides have gained considerable importance with the discovery of hydantocidin, a natural spironucleoside isolated from fermentation broths of Streptomyces hygroscopicus which exhibits potent herbicidal activity. The biological activity of hydantocidin has prompted considerable synthetic interest in this nucleoside and also in a variety of analogues, since important pharmaceutical leads can be found among modified nucleoside analogues. We present here an overview of the most important advances in the synthesis of spironucleosides. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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6014 KiB

Open AccessReview

Recent Advances in the Synthesis of Spiroheterocycles via N-Heterocyclic Carbene Organocatalysis

by Yue Liu, Xiang Zhang, Rong Zeng, Ying Zhang, Qing-Song Dai, Hai-Jun Leng, Xiao-Jun Gou and Jun-Long Li

Molecules 2017, 22(11), 1882; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules22111882 - 08 Nov 2017

Cited by 33 | Viewed by 7316

Abstract

Spiroheterocycles are regarded as a privileged framework because of their wide distribution in various natural products and synthetic molecules and promising bioactivities. This review focuses on the recent advances in the synthesis of spiroheterocycles by using the strategy of N-heterocyclic carbene (NHC) organocatalysis, and is organized based on the stereoselectivity and the reactive intermediates. According to the stereochemistry, this review was divided into two main parts, covering racemic and enantioselective versions. In each part, we firstly describe the synthetic transformations using nucleophilic Breslow intermediates, and then discuss the reactions that employ electrophilic acylazolium or radical cation intermediates. With those distinct catalytic activation modes of NHC organocatlysis, we expect this synthetic protocol will possibly produce new molecules with structural novelty and complexity, which may warrant further research in the field of drug discovery. Full article

(This article belongs to the Special Issue Advances in Spiro Compounds)

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