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19 pages, 5103 KiB

Open AccessArticle

Reusable Glucose-Based Crown Ethers Anchored to PVC

by Bertalan Varga, Dóra Ujj, Béla Mátravölgyi, Beáta Szolnoki, Béla Koczka and Zsolt Rapi

Molecules 2023, 28(23), 7905; https://doi.org/10.3390/molecules28237905 - 2 Dec 2023

Cited by 1 | Viewed by 751

Abstract

The recovery and reuse of the enantioselective catalysts produced by tedious work are important not only from the perspective of green chemistry, but also from the point of view of productivity. Some of the carbohydrate-based crown ethers prepared in our research group were [...] Read more.

The recovery and reuse of the enantioselective catalysts produced by tedious work are important not only from the perspective of green chemistry, but also from the point of view of productivity. Some of the carbohydrate-based crown ethers prepared in our research group were able to generate significant asymmetric induction in certain cases. However, they were not recoverable after the synthesis. Therefore, we modified the most effective structure with a propargyl group so that it can be attached to a polymer with an azide–alkyne reaction. It was investigated whether the position of the bonding affects the activity of the crown ethers, hence, the propargyl group was introduced either to the side chain, to the anomeric center or to the benzylidene protecting group. To anchor the macrocycles, low molecular weight PVC was modified with azide groups in 4% and 10%, respectively. It was found that glucose-based crown ether bearing the propargyl group on the benzylidene unit and grafted to PVC in 4% has the highest activity regarding the enantioselectivity (77% ee). The catalyst was recoverable in the Michael addition of diethyl acetamidomalonate to nitrostyrene and it could be reused five times without the loss of enantioselectivity. Full article

(This article belongs to the Special Issue Recent Advances of Catalytic Asymmetric Synthesis)

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15 pages, 5075 KiB

Open AccessArticle

Palladium-Catalyzed Stereoselective Construction of 1,3-Stereocenters Displaying Axial and Central Chirality via Asymmetric Alkylations

by Aiqi Xue, Xingfu Wei, Yue Huang, Jingping Qu and Baomin Wang

Molecules 2023, 28(7), 2927; https://doi.org/10.3390/molecules28072927 - 24 Mar 2023

Cited by 1 | Viewed by 1116

Abstract

The concurrent construction of 1,3-stereocenters remains a challenge. Herein, we report the development of stereoselective union of a point chiral center with allenyl axial chirality in 1,3-position by Pd-catalyzed asymmetric allenylic alkylation between racemic allenyl carbonates and indanone-derived β-ketoesters. Various target products bearing [...] Read more.

The concurrent construction of 1,3-stereocenters remains a challenge. Herein, we report the development of stereoselective union of a point chiral center with allenyl axial chirality in 1,3-position by Pd-catalyzed asymmetric allenylic alkylation between racemic allenyl carbonates and indanone-derived β-ketoesters. Various target products bearing a broad range of functional groups were afforded in high yield (up to 99%) with excellent enantioselectivities (up to 98% ee) and good diastereoselectivities (up to 13:1 dr). Full article

(This article belongs to the Special Issue Recent Advances of Catalytic Asymmetric Synthesis)

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Scheme 1

10 pages, 1329 KiB

Open AccessCommunication

Chiral Phosphine Catalyzed Allylic Alkylation of Benzylidene Succinimides with Morita–Baylis–Hillman Carbonates

by Chang Liu, Jianwei Sun and Pengfei Li

Molecules 2023, 28(6), 2825; https://doi.org/10.3390/molecules28062825 - 21 Mar 2023

Cited by 3 | Viewed by 1336

Abstract

Owing to their unique chemical properties, α-alkylidene succinimides generally act as versatile synthons in organic synthesis. Compared with well-established annulations, nucleophilic alkylations of α-alkylidene succinimides are very limited. Accordingly, an organocatalytic allylic alkylation of α-benzylidene succinimides with Morita–Baylis–Hillman (MBH) carbonates was established. In [...] Read more.

Owing to their unique chemical properties, α-alkylidene succinimides generally act as versatile synthons in organic synthesis. Compared with well-established annulations, nucleophilic alkylations of α-alkylidene succinimides are very limited. Accordingly, an organocatalytic allylic alkylation of α-benzylidene succinimides with Morita–Baylis–Hillman (MBH) carbonates was established. In the presence of a chiral phosphine catalyst, α-benzylidene succinimides reacted smoothly with MBH carbonates under mild conditions to furnish a series of optical active succinimides in high yields and enantioselectivities. Different from the reported results, the organocatalytic enantioselective construction of pyrrolidine-2,5-dione frameworks bearing contiguous chiral tertiary carbon centers was achieved via this synthetic strategy. Scaling up the reaction indicated that it is a practical strategy for the organocatalytic enantioselective alkylation of α-alkylidene succinimides. A possible reaction mechanism was also proposed. Full article

(This article belongs to the Special Issue Recent Advances of Catalytic Asymmetric Synthesis)

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Scheme 1

14 pages, 1866 KiB

Open AccessArticle

Copper-Catalyzed Asymmetric Dearomative [3+2] Cycloaddition of Nitroheteroarenes with Azomethines

by Yan Chen, Jian-Qiang Zhao, Yan-Ping Zhang, Ming-Qiang Zhou, Xiao-Mei Zhang and Wei-Cheng Yuan

Molecules 2023, 28(6), 2765; https://doi.org/10.3390/molecules28062765 - 19 Mar 2023

Cited by 1 | Viewed by 1712

Abstract

Catalytic asymmetric dearomative [3+2] cycloaddition of α-imino γ-lactones with either 3-nitroindoles or 2-nitrobenzofurans by using a chiral copper complex as the catalyst was developed. A wide range of structurally diverse polyheterocyclic compounds containing spirocyclic-fused butyrolactone-pyrrolidine-indoline and butyrolactone–pyrrolidine–dihydrobenzofuran skeletons could be smoothly [...] Read more.

Catalytic asymmetric dearomative [3+2] cycloaddition of α-imino γ-lactones with either 3-nitroindoles or 2-nitrobenzofurans by using a chiral copper complex as the catalyst was developed. A wide range of structurally diverse polyheterocyclic compounds containing spirocyclic-fused butyrolactone-pyrrolidine-indoline and butyrolactone–pyrrolidine–dihydrobenzofuran skeletons could be smoothly obtained with excellent results (>99:1 dr and 98% ee). The potential synthetic applications of this methodology were also demonstrated by the scale-up experiment and by the diverse transformations of one product. This method is characterized by high asymmetric induction, wide functional group tolerance and scalability, and attractive product diversification. Full article

(This article belongs to the Special Issue Recent Advances of Catalytic Asymmetric Synthesis)

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16 pages, 2681 KiB

Open AccessArticle

Zinc-Catalyzed Enantioselective [3 + 3] Annulation for Synthesis of Chiral Spiro[indoline-3,4′-thiopyrano[2,3-b]indole] Derivatives

by Tian-Tian Liu, Yu Chen, Guang-Jian Mei, Yuan-Zhao Hua, Shi-Kun Jia and Min-Can Wang

Molecules 2023, 28(3), 1056; https://doi.org/10.3390/molecules28031056 - 20 Jan 2023

Cited by 8 | Viewed by 1430

Abstract

With a dinuclear zinc-ProPhenol complex as a catalyst, an efficient and novel [3 + 3] annulation of indoline-2-thiones and isatylidene malononitriles has been successfully developed via the Brønsted base and Lewis acid cooperative activation model. This practical methodology gives access to a broad [...] Read more.

With a dinuclear zinc-ProPhenol complex as a catalyst, an efficient and novel [3 + 3] annulation of indoline-2-thiones and isatylidene malononitriles has been successfully developed via the Brønsted base and Lewis acid cooperative activation model. This practical methodology gives access to a broad range of chiral spiro[indoline-3,4′-thiopyrano[2,3-b]indole] derivatives in good yields with excellent levels of enantioselectivities (up to 88% yield and 99% ee). Full article

(This article belongs to the Special Issue Recent Advances of Catalytic Asymmetric Synthesis)

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8 pages, 2620 KiB

Open AccessFeature PaperArticle

Ir-Catalyzed Chemo-, Regio-, and Enantioselective Allylic Enolization of 6,6-Dimethyl-3-((trimethylsilyl)oxy)cyclohex-2-en-1-one Involving Keto-Enol Isomerization

by Xiao-Lin Wang, Ji-Teng Chen, Sheng-Cai Zheng and Xiao-Ming Zhao

Molecules 2022, 27(20), 6981; https://doi.org/10.3390/molecules27206981 - 17 Oct 2022

Viewed by 1342

Abstract

The utilization of 6,6-dimethyl-3-((trimethylsilyl)oxy)cyclohex-2-en-1-one made from an unsymmetrical 4,4-dimethylcyclohexane-1,3-dione in iridium-catalyzed allylic enolization involving keto-enol isomerization is accomplished under mild conditions. The chemoselectivity, regioselectivity, and enantioselectivity are facilitated by the quaternary carbon and adjusting the reaction conditions. This method provides the substituted 2-(but-3-en-2-yl)-3-hydroxy-6,6-dimethylcyclohex-2-en-1-ones [...] Read more.

The utilization of 6,6-dimethyl-3-((trimethylsilyl)oxy)cyclohex-2-en-1-one made from an unsymmetrical 4,4-dimethylcyclohexane-1,3-dione in iridium-catalyzed allylic enolization involving keto-enol isomerization is accomplished under mild conditions. The chemoselectivity, regioselectivity, and enantioselectivity are facilitated by the quaternary carbon and adjusting the reaction conditions. This method provides the substituted 2-(but-3-en-2-yl)-3-hydroxy-6,6-dimethylcyclohex-2-en-1-ones in good to high yields with high level of chemo-, regio-, and enantioselectivities. The chiral carbon-fluorine bond formation is induced by an adjacent chiral carbon center of the allylated 3-hydroxy-6,6-dimethylcyclohex-2-en-1-one, as well. Full article

(This article belongs to the Special Issue Recent Advances of Catalytic Asymmetric Synthesis)

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17 pages, 3577 KiB

Open AccessArticle

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

by Dong-Hua Xie, Cheng Niu and Da-Ming Du

Molecules 2022, 27(16), 5081; https://doi.org/10.3390/molecules27165081 - 10 Aug 2022

Cited by 3 | Viewed by 1319

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Recent Advances of Catalytic Asymmetric Synthesis)

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Review

Jump to: Research

53 pages, 34688 KiB

Open AccessReview

Progress in Catalytic Asymmetric Reactions with 7-Azaindoline as the Directing Group

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

Molecules 2023, 28(23), 7898; https://doi.org/10.3390/molecules28237898 - 1 Dec 2023

Viewed by 709

Abstract

α-Substituted-7-azaindoline amides and α,β-unsaturated 7-azaindoline amides have emerged as new versatile synthons for various metal-catalyzed and organic-catalyzed asymmetric reactions, which have attracted much attention from chemists. In this review, the progress of research on 7-azaindoline amides in the asymmetric aldol reaction, the Mannich [...] Read more.

α-Substituted-7-azaindoline amides and α,β-unsaturated 7-azaindoline amides have emerged as new versatile synthons for various metal-catalyzed and organic-catalyzed asymmetric reactions, which have attracted much attention from chemists. In this review, the progress of research on 7-azaindoline amides in the asymmetric aldol reaction, the Mannich reaction, the conjugate addition, the 1,3-dipole cycloaddition, the Michael/aldol cascade reaction, aminomethylation and the Michael addition-initiated ring-closure reaction is discussed. The α-substituted-7-azaindoline amides, as nucleophiles, are classified according to the type of α-substituted group, whereas the α,β-unsaturated 7-azaindoline amides, as electrophiles, are classified according to the type of reaction. Full article

(This article belongs to the Special Issue Recent Advances of Catalytic Asymmetric Synthesis)

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42 pages, 8597 KiB

Open AccessReview

Recent Advances of N-2,2,2-Trifluoroethylisatin Ketimines in Organic Synthesis

by Yuting Liu, Lijie Wang, Donglai Ma and Yongxing Song

Molecules 2023, 28(7), 2990; https://doi.org/10.3390/molecules28072990 - 27 Mar 2023

Cited by 3 | Viewed by 1365

Abstract

The special properties of fluorine atoms and fluorine-containing groups have led to an increasing number of applications for fluorine-containing organic compounds, which are also extremely widely used in the field of new drug development. Unfortunately, naturally fluorinated organics are rare in nature, so [...] Read more.

The special properties of fluorine atoms and fluorine-containing groups have led to an increasing number of applications for fluorine-containing organic compounds, which are also extremely widely used in the field of new drug development. Unfortunately, naturally fluorinated organics are rare in nature, so the selective introduction of fluorine atoms or fluorine-containing groups into organic molecules is very important for pharmaceutical/synthetic chemists. N-2,2,2-trifluoroethylisatin ketimines have received the attention of many chemists since they were first developed as fluorine-containing synthons in 2015. This paper reviews the organic synthesis reactions in which trifluoroethyl isatin ketimine has been involved in recent years, focusing on the types of reactions and the stereoselectivity of products, and also provides a prospect of its application in this field. Full article

(This article belongs to the Special Issue Recent Advances of Catalytic Asymmetric Synthesis)

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