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12 pages, 6172 KiB

Open AccessArticle

Synthesis of Tetrasubstituted Nitroalkenes and Preliminary Studies of Their Enantioselective Organocatalytic Reduction

by Patricia Camarero González, Sergio Rossi, Miguel Sanz, Francesca Vasile and Maurizio Benaglia

Molecules 2023, 28(7), 3156; https://doi.org/10.3390/molecules28073156 - 01 Apr 2023

Cited by 1 | Viewed by 1226

Abstract

Starting from commercially available ketones, a reproducible and reliable strategy for the synthesis of tetrasubstituted nitroalkenes was successfully developed, using a two-step procedure; the HWE olefination of the ketone to form the corresponding α,β-unsaturated esters is followed by a nitration reaction to introduce [...] Read more.

Starting from commercially available ketones, a reproducible and reliable strategy for the synthesis of tetrasubstituted nitroalkenes was successfully developed, using a two-step procedure; the HWE olefination of the ketone to form the corresponding α,β-unsaturated esters is followed by a nitration reaction to introduce the nitro group in the α position of the ester group. The enantioselective organocatalytic reduction of these compounds has also been preliminarily studied, to access the functionalized enantioenriched nitroalkanes, which are useful starting materials for further synthetic elaborations. The absolute configuration of the reduction product was established by chemical correlation of the chiral nitroalkane with a known product; preliminary DFT calculations were also conducted to rationalize the stereochemical outcome of the organocatalytic enantioselective reduction. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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10 pages, 5106 KiB

Open AccessCommunication

Novel Synthesis of Dihydroisoxazoles by p-TsOH-Participated 1,3-Dipolar Cycloaddition of Dipolarophiles withα-Nitroketones

by Caiyun Yang, Sirou Hu, Xinhui Pan, Ke Yang, Ke Zhang, Qingguang Liu, Xiaobing Xin, Jie Li, Jinhui Wang and Xiaoda Yang

Molecules 2023, 28(6), 2565; https://doi.org/10.3390/molecules28062565 - 11 Mar 2023

Cited by 1 | Viewed by 1279

Abstract

This article reports in detail a method for the synthesis of 3-benzoxoxazoline by the reaction of alkenes (alkynes) and a variety of α-nitroketones in the presence of p-TsOH. The scope of alkenes is broad, including different alkenes and the alkyne. This reaction [...] Read more.

This article reports in detail a method for the synthesis of 3-benzoxoxazoline by the reaction of alkenes (alkynes) and a variety of α-nitroketones in the presence of p-TsOH. The scope of alkenes is broad, including different alkenes and the alkyne. This reaction provides a convenient and efficient synthetic method of 3-benzoylisoxazolines. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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17 pages, 3010 KiB

Open AccessArticle

Synthesis and Catalytic Activity of Bifunctional Phase-Transfer Organocatalysts Based on Camphor

by Luka Ciber, Franc Požgan, Helena Brodnik, Bogdan Štefane, Jurij Svete, Mario Waser and Uroš Grošelj

Molecules 2023, 28(3), 1515; https://doi.org/10.3390/molecules28031515 - 03 Feb 2023

Cited by 4 | Viewed by 1818

Abstract

Ten novel bifunctional quaternary ammonium salt phase-transfer organocatalysts were synthesized in four steps from (+)-camphor-derived 1,3-diamines. These quaternary ammonium salts contained either (thio)urea or squaramide hydrogen bond donor groups in combination with either trifluoroacetate or iodide as the counteranion. Their organocatalytic activity was [...] Read more.

Ten novel bifunctional quaternary ammonium salt phase-transfer organocatalysts were synthesized in four steps from (+)-camphor-derived 1,3-diamines. These quaternary ammonium salts contained either (thio)urea or squaramide hydrogen bond donor groups in combination with either trifluoroacetate or iodide as the counteranion. Their organocatalytic activity was evaluated in electrophilic heterofunctionalizations of β-keto esters and in the Michael addition of a glycine Schiff base with methyl acrylate. α-Fluorination and chlorination of β-keto esters proceeded with full conversion and low enantioselectivities (up to 29% ee). Similarly, the Michael addition of a glycine Schiff base with methyl acrylate proceeded with full conversion and up to 11% ee. The new catalysts have been fully characterized; the stereochemistry at the C-2 chiral center was unambiguously determined. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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14 pages, 1659 KiB

Open AccessArticle

Unexpected Decarbonylation of Acylethynylpyrroles under the Action of Cyanomethyl Carbanion: A Robust Access to Ethynylpyrroles

by Denis N. Tomilin, Lyubov N. Sobenina, Alexandra M. Belogolova, Alexander B. Trofimov, Igor A. Ushakov and Boris A. Trofimov

Molecules 2023, 28(3), 1389; https://doi.org/10.3390/molecules28031389 - 01 Feb 2023

Cited by 1 | Viewed by 1166

Abstract

It has been found that the addition of CH₂CN⁻ anion to the carbonyl group of acylethynylpyrroles, generated from acetonitrile and t-BuOK, results in the formation of acetylenic alcohols, which undergo unexpectedly easy (room temperature) decomposition to ethynylpyrroles and cyanomethylphenylketones [...] Read more.

It has been found that the addition of CH₂CN⁻ anion to the carbonyl group of acylethynylpyrroles, generated from acetonitrile and t-BuOK, results in the formation of acetylenic alcohols, which undergo unexpectedly easy (room temperature) decomposition to ethynylpyrroles and cyanomethylphenylketones (retro-Favorsky reaction). This finding allows a robust synthesis of ethynylpyrroles in up to 95% yields to be developed. Since acylethynylpyrroles became available, the strategy thus found makes ethynylpyrroles more accessible than earlier. The quantum-chemical calculations (B2PLYP/6-311G**//B3LYP/6-311G**+C-PCM/acetonitrile) confirm the thermodynamic preference of the decomposition of the intermediate acetylenic alcohols to free ethynylpyrroles rather than their potassium derivatives. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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12 pages, 2640 KiB

Open AccessArticle

Two-Step Synthesis, Structure, and Optical Features of a Double Hetero[7]helicene

by Mohamed S. H. Salem, Ahmed Sabri, Md. Imrul Khalid, Hiroaki Sasai and Shinobu Takizawa

Molecules 2022, 27(24), 9068; https://doi.org/10.3390/molecules27249068 - 19 Dec 2022

Cited by 4 | Viewed by 3138

Abstract

A novel double aza-oxa[7]helicene was synthesized from the commercially available N¹,N⁴-di(naphthalen-2-yl)benzene-1,4-diamine and p-benzoquinone in two steps. Combining the acid-mediated annulation with the electrochemical sequential reaction (oxidative coupling and dehydrative cyclization) afforded this double hetero[7]helicene. Moreover, the structural [...] Read more.

A novel double aza-oxa[7]helicene was synthesized from the commercially available N¹,N⁴-di(naphthalen-2-yl)benzene-1,4-diamine and p-benzoquinone in two steps. Combining the acid-mediated annulation with the electrochemical sequential reaction (oxidative coupling and dehydrative cyclization) afforded this double hetero[7]helicene. Moreover, the structural and optical features of this molecule have been studied using X-ray crystallographic analysis, and the absorption and emission behaviors were rationalized based on DFT calculations. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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12 pages, 1602 KiB

Open AccessArticle

Copper-Catalyzed Asymmetric Sulfonylative Desymmetrization of Glycerol

by Kosuke Yamamoto, Keisuke Miyamoto, Mizuki Ueno, Yuki Takemoto, Masami Kuriyama and Osamu Onomura

Molecules 2022, 27(24), 9025; https://doi.org/10.3390/molecules27249025 - 18 Dec 2022

Cited by 1 | Viewed by 1773

Abstract

Glycerol is the main side product in the biodiesel manufacturing process, and the development of glycerol valorization methods would indirectly contribute the sustainable biodiesel production and decarbonization. Transformation of glycerol to optically active C3 units would be one of the attractive routes for [...] Read more.

Glycerol is the main side product in the biodiesel manufacturing process, and the development of glycerol valorization methods would indirectly contribute the sustainable biodiesel production and decarbonization. Transformation of glycerol to optically active C3 units would be one of the attractive routes for glycerol valorization. We herein present the asymmetric sulfonylative desymmetrization of glycerol by using a CuCN/(R,R)-PhBOX catalyst system to provide an optically active monosulfonylated glycerol in high efficiency. A high degree of enantioselectivity was achieved with a commercially available chiral ligand and an inexpensive carbonate base. The optically active monosulfonylated glycerol was successfully transformed into a C3 unit attached with differentially protected three hydroxy moieties. In addition, the synthetic utility of the present reaction was also demonstrated by the transformation of the monosulfonylated glycerol into an optically active synthetic ceramide, sphingolipid E. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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14 pages, 2543 KiB

Open AccessArticle

The Use of Aryl-Substituted Homophthalic Anhydrides in the Castagnoli–Cushman Reaction Provides Access to Novel Tetrahydroisoquinolone Carboxylic Acid Bearing an All-Carbon Quaternary Stereogenic Center

by Nazar Moshnenko, Alexander Kazantsev, Olga Bakulina, Dmitry Dar’in and Mikhail Krasavin

Molecules 2022, 27(23), 8462; https://doi.org/10.3390/molecules27238462 - 02 Dec 2022

Cited by 3 | Viewed by 1275

Abstract

Novel aryl-substituted homophthalic acids were cyclodehydrated to the respective homophthalic anhydrides for use in the Castagnoli–Cushman reaction. With a range of imines, this reaction proceeded smoothly and delivered hitherto undescribed 4-aryl-substituted tetrahydroisoquinolonic acids with remarkable diastereoselectivity, good yields and no need for chromatographic [...] Read more.

Novel aryl-substituted homophthalic acids were cyclodehydrated to the respective homophthalic anhydrides for use in the Castagnoli–Cushman reaction. With a range of imines, this reaction proceeded smoothly and delivered hitherto undescribed 4-aryl-substituted tetrahydroisoquinolonic acids with remarkable diastereoselectivity, good yields and no need for chromatographic purification. These findings significantly extend the range of cyclic anhydrides employable in the Castagnoli–Cushman reaction and signify access to a novel substitution pattern around the medicinally relevant tetrahydroisoquinolonic acid scaffold. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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8 pages, 559 KiB

Open AccessArticle

An Improved Synthetic Method for Sensitive Iodine Containing Tricyclic Flavonoids

by Mihail Lucian Birsa and Laura G. Sarbu

Molecules 2022, 27(23), 8430; https://doi.org/10.3390/molecules27238430 - 02 Dec 2022

Cited by 1 | Viewed by 828

Abstract

The synthesis of new iodine containing synthetic tricyclic flavonoids is reported. Due to the sensitivity of the precursors to the heat and acidic conditions required for the ring closure of the 1,3-dithiolium core, a new cyclization method has been developed. It consists in [...] Read more.

The synthesis of new iodine containing synthetic tricyclic flavonoids is reported. Due to the sensitivity of the precursors to the heat and acidic conditions required for the ring closure of the 1,3-dithiolium core, a new cyclization method has been developed. It consists in the treatment of the corresponding iodine-substituted 3-dithiocarbamic flavonoids with a 1:1 (v/v) mixture of glacial acetic acid–concentrated sulfuric acid at 40 °C. The synthesis of the iodine-substituted 3-dithiocarbamic flavonoids has also been tuned in terms of reaction conditions. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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16 pages, 1314 KiB

Open AccessFeature PaperArticle

Preparation of Chiral Enantioenriched Densely Substituted Cyclopropyl Azoles, Amines, and Ethers via Formal S_N2′ Substitution of Bromocylopropanes

by Hillary Straub, Pavel Ryabchuk, Marina Rubina and Michael Rubin

Molecules 2022, 27(20), 7069; https://doi.org/10.3390/molecules27207069 - 20 Oct 2022

Viewed by 1746

Abstract

Enantiomerically enriched cyclopropyl ethers, amines, and cyclopropylazole derivatives possessing three stereogenic carbon atoms in a small cycle are obtained via the diastereoselective, formal nucleophilic substitution of chiral, non-racemic bromocyclopropanes. The key feature of this methodology is the utilization of the chiral center of [...] Read more.

Enantiomerically enriched cyclopropyl ethers, amines, and cyclopropylazole derivatives possessing three stereogenic carbon atoms in a small cycle are obtained via the diastereoselective, formal nucleophilic substitution of chiral, non-racemic bromocyclopropanes. The key feature of this methodology is the utilization of the chiral center of the cyclopropene intermediate, which governs the configuration of the two adjacent stereocenters that are successively installed via 1,4-addition/epimerization sequence. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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15 pages, 1717 KiB

Open AccessArticle

Efficient Synthesis of 2-OH Thioglycosides from Glycals Based on the Reduction of Aryl Disulfides by NaBH₄

by Yang-Fan Guo, Tao Luo, Guang-Jing Feng, Chun-Yang Liu and Hai Dong

Molecules 2022, 27(18), 5980; https://doi.org/10.3390/molecules27185980 - 14 Sep 2022

Cited by 3 | Viewed by 1532

Abstract

An improved method to efficiently synthesize 2-OH thioaryl glycosides starting from corresponding per-protected glycals was developed, where 1,2-anhydro sugars were prepared by the oxidation of glycals with oxone, followed by reaction of crude crystalline 1,2-anhydro sugars with NaBH₄ and aryl disulfides. This [...] Read more.

An improved method to efficiently synthesize 2-OH thioaryl glycosides starting from corresponding per-protected glycals was developed, where 1,2-anhydro sugars were prepared by the oxidation of glycals with oxone, followed by reaction of crude crystalline 1,2-anhydro sugars with NaBH₄ and aryl disulfides. This method has been further used in a one-pot reaction to synthesize glycosyl donors having both “armed” and “NGP (neighboring group participation)” effects. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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16 pages, 5486 KiB

Open AccessArticle

Non-Palladium-Catalyzed Approach to the Synthesis of (E)-3-(1,3-Diarylallylidene)Oxindoles

by Jahyun Koo, Minsu Kim, Kye Jung Shin and Jae Hong Seo

Molecules 2022, 27(16), 5304; https://doi.org/10.3390/molecules27165304 - 19 Aug 2022

Viewed by 1270

Abstract

Two novel synthetic approaches for synthesizing (E)-3-(1,3-diarylallylidene)oxindoles from oxindole were developed. All previously reported methods for synthesizing 3-(1,3-diarylallylidene)oxindoles utilized palladium-catalyzed reactions as a key step to form this unique skeleton. Despite high efficiency, palladium-catalyzed reactions have limitations in terms of substrate [...] Read more.

Two novel synthetic approaches for synthesizing (E)-3-(1,3-diarylallylidene)oxindoles from oxindole were developed. All previously reported methods for synthesizing 3-(1,3-diarylallylidene)oxindoles utilized palladium-catalyzed reactions as a key step to form this unique skeleton. Despite high efficiency, palladium-catalyzed reactions have limitations in terms of substrate scope. Especially, an iodoaryl moiety cannot be introduced by the previous methods due to its high reactivity toward the palladium catalyst. Our Knoevenagel/allylic oxidation/Wittig and Knoevenagel/aldol/dehydration strategies complement each other and show broad substrate scope, including substrates with iodoaryl groups. The current methods utilized acetophenones, benzylidene phosphonium ylides, and benzaldehydes that are commercially available or easily accessible. Thus, the current synthetic approaches to (E)-3-(1,3-diarylallyldiene)oxindoles are readily amendable for variety of oxindole derivatives. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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Review

Jump to: Research

25 pages, 12511 KiB

Open AccessReview

Recent Advances in Gold(I)-Catalyzed Approaches to Three-Type Small-Molecule Scaffolds via Arylalkyne Activation

by Lu Yang, Hongwei Su, Yue Sun, Sen Zhang, Maosheng Cheng and Yongxiang Liu

Molecules 2022, 27(24), 8956; https://doi.org/10.3390/molecules27248956 - 15 Dec 2022

Cited by 2 | Viewed by 1785

Abstract

Gold catalysts possess the advantages of water and oxygen resistance, with the possibility of catalyzing many novel chemical transformations, especially in the syntheses of small-molecule skeletons, in addition to achieving the rapid construction of multiple chemical bonds and ring systems in one step. [...] Read more.

Gold catalysts possess the advantages of water and oxygen resistance, with the possibility of catalyzing many novel chemical transformations, especially in the syntheses of small-molecule skeletons, in addition to achieving the rapid construction of multiple chemical bonds and ring systems in one step. In this feature paper, we summarize recent advances in the construction of small-molecule scaffolds, such as benzene, cyclopentene, furan, and pyran, based on gold-catalyzed cyclization of arylalkyne derivatives within the last decade. We hope that this review will serve as a useful reference for chemists to apply gold-catalyzed strategies to the syntheses of related natural products and active molecules, hopefully providing useful guidance for the exploration of additional novel gold-catalyzed approaches. Full article

(This article belongs to the Special Issue New Approaches to Synthetic Organic Chemistry)

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