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16 pages, 1891 KiB

Open AccessArticle

Iodine-Catalyzed Cascade Annulation of 4-Hydroxycoumarins with Aurones: Access to Spirocyclic Benzofuran–Furocoumarins

by Xuequan Wang, Changhui Yang, Dan Yue, Mingde Xu, Suyue Duan and Xianfu Shen

Molecules 2024, 29(8), 1701; https://doi.org/10.3390/molecules29081701 - 09 Apr 2024

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An attractive approach for the preparation of spirocyclic benzofuran–furocoumarins has been developed through iodine-catalyzed cascade annulation of 4-hydroxycoumarins with aurones. The reaction involves Michael addition, iodination, and intramolecular nucleophilic substitution in a one-step process, and offers an efficient method for easy access to [...] Read more.

An attractive approach for the preparation of spirocyclic benzofuran–furocoumarins has been developed through iodine-catalyzed cascade annulation of 4-hydroxycoumarins with aurones. The reaction involves Michael addition, iodination, and intramolecular nucleophilic substitution in a one-step process, and offers an efficient method for easy access to a series of valuable spirocyclic benzofuran–furocoumarins in good yields (up to 99%) with excellent stereoselectivity. Moreover, this unprecedented protocol provides several advantages, including readily available materials, an environmentally benign catalyst, a broad substrate scope, and a simple procedure. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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15 pages, 3267 KiB

Open AccessArticle

LiO^tBu-Promoted Intramolecular 1,3-Dipolar Cycloaddition of the 2′-Alkynyl-biaryl-2-aldehyde N-Tosylhydrazones Approach to 3-Substituted 1H-Dibenzo[e,g]indazoles

by Jiaying Lv and Ruimao Hua

Molecules 2023, 28(24), 8061; https://doi.org/10.3390/molecules28248061 - 13 Dec 2023

Cited by 1 | Viewed by 640

Abstract

A two-step, one-pot synthesis of 3-substituted 1H-dibenzo[e,g]indazoles in good to high yields via a LiO^tBu-promoted intramolecular 1,3-dipolar cyclization of 2′-alkynyl-biaryl-2-aldehyde N-tosylhydrazones was developed. The N-Ts-hydrazones used were prepared in situ via the reactions [...] Read more.

A two-step, one-pot synthesis of 3-substituted 1H-dibenzo[e,g]indazoles in good to high yields via a LiO^tBu-promoted intramolecular 1,3-dipolar cyclization of 2′-alkynyl-biaryl-2-aldehyde N-tosylhydrazones was developed. The N-Ts-hydrazones used were prepared in situ via the reactions of 2′-alkynyl-biaryl-2-aldehydes and TsNHNH₂ (p-methylbenzenesulfonohydrazide). Two types of signals related to the hydrogen bonds, forming in several products, were observed in the ¹H NMR spectra recorded in DMSO-d₆, assigned to N-H bonds in their dimeric species of product and tautomer. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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14 pages, 2079 KiB

Open AccessArticle

Highly Selective Cyclization and Isomerization of Propargylamines to Access Functionalized Quinolines and 1-Azadienes

by Zheng-Guang Wu, Hui Zhang, Chenhui Cao, Chaowu Lu, Aiwei Jiang, Jie He, Qin Zhao and Yanfeng Tang

Molecules 2023, 28(17), 6259; https://doi.org/10.3390/molecules28176259 - 26 Aug 2023

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Abstract

Developing new organic reactions with excellent atom economy and high selectivity is significant and urgent. Herein, by ingeniously regulating the reaction conditions, highly selective transformations of propargylamines have been successfully implemented. The palladium-catalyzed cyclization of propargylamines generates a series of functionalized quinoline heterocycles, [...] Read more.

Developing new organic reactions with excellent atom economy and high selectivity is significant and urgent. Herein, by ingeniously regulating the reaction conditions, highly selective transformations of propargylamines have been successfully implemented. The palladium-catalyzed cyclization of propargylamines generates a series of functionalized quinoline heterocycles, while the base-promoted isomerization of propargylamines affords diverse 1-azadienes. Both reactions have good functional group tolerance, mild conditions, excellent atom economy and high yields of up to 93%. More importantly, these quinoline heterocycles and 1-azadienes could be flexibly transformed into valuable compounds, illustrating the validity and practicability of the propargylamine-based highly selective reactions. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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14 pages, 1960 KiB

Open AccessCommunication

Friedel–Crafts Reaction of Acylsilanes: Highly Chemoselective Synthesis of 1-Hydroxy-bis(indolyl)methanes and 1-Silyl-bis(indolyl)methanes Derivatives

by Qi Li, Xiu-Xia Liang, Wang Zhang and Man-Yi Han

Molecules 2023, 28(15), 5685; https://doi.org/10.3390/molecules28155685 - 27 Jul 2023

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Abstract

A novel double Friedel–Crafts reaction of acylsilanes in water is described. This strategy enables synthesis of bis(indolyl)methane derivatives with 1-hydroxy or 1-silyl substituents in moderate to high yield. Compared to the 1-silyl-bis(indolyl)methane derivatives from indole substrate, 1-hydroxy-bis(indolyl)methane derivatives were synthesized from the 5-hydroxyindole, [...] Read more.

A novel double Friedel–Crafts reaction of acylsilanes in water is described. This strategy enables synthesis of bis(indolyl)methane derivatives with 1-hydroxy or 1-silyl substituents in moderate to high yield. Compared to the 1-silyl-bis(indolyl)methane derivatives from indole substrate, 1-hydroxy-bis(indolyl)methane derivatives were synthesized from the 5-hydroxyindole, and the hydrogen bonds in the 5-hydroxyindole play a crucial role in regulating the reaction selectivity. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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13 pages, 1929 KiB

Open AccessArticle

Photoinduced Photocatalyst-Free Cascade Cyclization of Alkynes with Sodium Sulfinates for the Synthesis of Benzothiophenes and Thioflavones

by Hongqiang Dong, Chunli Chen, Jinlei Zhao, Yigang Ji and Wenchao Yang

Molecules 2023, 28(11), 4436; https://doi.org/10.3390/molecules28114436 - 30 May 2023

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Abstract

The subject of this investigation is a new method for the construction of sulfonylated heterocycles which overcomes the limitations of classical approaches using a cheap feedstock sulfonylating agent, especially under photocatalyst- and metal-free conditions. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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16 pages, 1642 KiB

Open AccessArticle

Substituent-Controllable Cascade Regioselective Annulation of β-Enaminones with N-Sulfonyl Triazoles for Modular Access to Imidazoles and Pyrroles

by Hua Wang, Tongtong Zhou, Mengdi Wu, Qingqing Ye and Xinwei He

Molecules 2023, 28(11), 4416; https://doi.org/10.3390/molecules28114416 - 29 May 2023

Cited by 1 | Viewed by 845

Abstract

A controllable synthesis of trisubstituted imidazoles and pyrroles has been developed through rhodium(II)-catalyzed regioselective annulation of N-sulfonyl-1,2,3-trizaoles with β-enaminones. The imidazole ring was formed through a 1,1-insertion of the N-H bond to α-imino rhodium carbene, followed by a subsequent intramolecular 1,4-conjugate [...] Read more.

A controllable synthesis of trisubstituted imidazoles and pyrroles has been developed through rhodium(II)-catalyzed regioselective annulation of N-sulfonyl-1,2,3-trizaoles with β-enaminones. The imidazole ring was formed through a 1,1-insertion of the N-H bond to α-imino rhodium carbene, followed by a subsequent intramolecular 1,4-conjugate addition. This occurred when the α-carbon atom of the amino group was bearing a methyl group. Additionally, the pyrrole ring was constructed by utilizing a phenyl substituent and undergoing intramolecular nucleophilic addition. The mild conditions, good tolerance towards functional groups, gram-scale synthesis capability, and ability to undergo valuable transformations of the products qualify this unique protocol as an efficient tool for the synthesis of N-heterocycles. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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14 pages, 2512 KiB

Open AccessArticle

Synthesis of 5,6-Dihydropyrazolo[5,1-a]isoquinolines through Tandem Reaction of C,N-Cyclic Azomethine Imines with α,β-Unsaturated Ketones

by Young Jae Yun and Sung-Gon Kim

Molecules 2023, 28(9), 3710; https://doi.org/10.3390/molecules28093710 - 25 Apr 2023

Viewed by 908

Abstract

An innovative and efficient approach has been developed for the synthesis of 5,6-dihydropyrazolo[5,1-a]isoquinolines. This one-pot tandem reaction involves the reaction of C,N-cyclic azomethine imines with α,β-unsaturated ketones, using K₂CO₃ as the base and DDQ as [...] Read more.

An innovative and efficient approach has been developed for the synthesis of 5,6-dihydropyrazolo[5,1-a]isoquinolines. This one-pot tandem reaction involves the reaction of C,N-cyclic azomethine imines with α,β-unsaturated ketones, using K₂CO₃ as the base and DDQ as the oxidant. The process results in functionalized 5,6-dihydropyrazolo[5,1-a]isoquinolines with good yields. This convenient one-step method encompasses a tandem [3 + 2]-cycloaddition, detosylation, and oxidative aromatization. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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15 pages, 2358 KiB

Open AccessArticle

Base-Promoted Intramolecular Addition of Vinyl Cyclopropanecarboxamides to Access Conformationally Restricted Aza[3.1.0]bicycles

by Jingya Li, Zhiguo Zhang, Liming Chen, Mengjuan Li, Xingjie Zhang and Guisheng Zhang

Molecules 2023, 28(9), 3691; https://doi.org/10.3390/molecules28093691 - 25 Apr 2023

Viewed by 1374

Abstract

3-Azabicyclo[3.1.0]hexanes are common structural components in natural products and bioactive compounds. Traditionally, the metal-mediated cyclopropanation domino reaction of chain enzymes is the most commonly used strategy for the construction of this type of aza[3.1.0]bicycle derivative. In this study, a base-promoted intramolecular addition of [...] Read more.

3-Azabicyclo[3.1.0]hexanes are common structural components in natural products and bioactive compounds. Traditionally, the metal-mediated cyclopropanation domino reaction of chain enzymes is the most commonly used strategy for the construction of this type of aza[3.1.0]bicycle derivative. In this study, a base-promoted intramolecular addition of alkenes used to deliver conformationally restricted highly substituted aza[3.1.0]bicycles is reported. This reaction was tailor-made for saturated aza[3.1.0] bicycle-containing fused bicyclic compounds that may be applied in the development of concise and divergent total syntheses of bioactive compounds. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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20 pages, 1510 KiB

Open AccessArticle

Acid/Base-Steered Cascade Cyclization: An Efficient One-Pot Access to Diverse Isobenzofuranone and Isoindolobenzoxazinone Derivatives

by Ran Shi, Xiangmin Wang, Xuesi Zhang, Sen Chen, Zu-Li Wang, Huijing Qi and Xin-Ming Xu

Molecules 2023, 28(3), 1443; https://doi.org/10.3390/molecules28031443 - 02 Feb 2023

Viewed by 1362

Abstract

We herein report the acid/base-steered two distinct reaction pathways of 2-acylbenzoic acids with isatoic anhydrides. In the presence of Na₂CO₃, the cascade process consists of the cyclization of 2-acetylbenzoic acid and nucleophilic ring-opening reaction of isatoic anhydride to furnish [...] Read more.

We herein report the acid/base-steered two distinct reaction pathways of 2-acylbenzoic acids with isatoic anhydrides. In the presence of Na₂CO₃, the cascade process consists of the cyclization of 2-acetylbenzoic acid and nucleophilic ring-opening reaction of isatoic anhydride to furnish isobenzofuranone derivatives with high efficiency. However, p-toluenesulfonic acid can promote the product isobenzofuranones to undergo sequential intramolecular rearrangment, nucleophilic addition and cyclization reaction to produce diverse isoindolobenzoxazinones in good yields. The synthetic utility of this method was further demonstrated by the gram-scale preparation of the desired products and the facile transformations of the resulting products. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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Review

Jump to: Research

40 pages, 9745 KiB

Open AccessReview

Recent Progress in Heterocycle Synthesis: Cyclization Reaction with Pyridinium and Quinolinium 1,4-Zwitterions

by Zhen-Hua Wang, Yong You, Jian-Qiang Zhao, Yan-Ping Zhang, Jun-Qing Yin and Wei-Cheng Yuan

Molecules 2023, 28(7), 3059; https://doi.org/10.3390/molecules28073059 - 29 Mar 2023

Cited by 3 | Viewed by 1854

Abstract

Heteroarene 1, n-zwitterions are powerful and versatile building blocks in the construction of heterocycles and have received increasing attention in recent years. In particular, pyridinium and quinolinium 1,4-zwitterions have been widely studied and used in a variety of cyclization reactions due to their [...] Read more.

Heteroarene 1, n-zwitterions are powerful and versatile building blocks in the construction of heterocycles and have received increasing attention in recent years. In particular, pyridinium and quinolinium 1,4-zwitterions have been widely studied and used in a variety of cyclization reactions due to their air stability, ease of use, and high efficiency. Sulfur- and nitrogen-based pyridinium and quinolinium 1,4-zwitterions, types of emerging heteroatom-containing synthons, have attracted much attention from chemists. These 1,4-zwitterions, which contain multiple reaction sites, have been successfully used in the synthesis of three- to eight-membered cyclic compounds over the last decade. In this review, we present the exciting progress made in the field of cyclization reactions of sulfur- and nitrogen-based pyridinium and quinolinium 1,4-zwitterions. Moreover, the mechanistic insights, the transition states, some synthetic applications, and the challenges and opportunities are also discussed. We hope to provide an overview for synthetic chemists who are interested in the heterocycle synthesis from cyclization reaction with pyridinium and quinolinium 1,4-zwitterions pyridinium and quinolinium 1,4-zwitterions. Full article

(This article belongs to the Special Issue Novel Organic Synthetic Route to Heterocyclic Compounds)

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