scholarly journals Ring-opening and ring-expansion reactions of carborane-fused borirane

2021 ◽  
Vol 12 (39) ◽  
pp. 13187-13192
Author(s):  
Hanqiang Wang ◽  
Jie Zhang ◽  
Zuowei Xie
Keyword(s):  
Lewis Acids ◽  
Ring Opening ◽  
Ring Expansion ◽  
Ring Opening Reactions ◽  
Different Types

Carborane-fused borirane can not only engage in ring-opening reactions with different types of Lewis acids, but also undergo ring-expansion reactions with unsaturated molecules such as PhCHO, CO2 and PhCN to give five-membered boracycles.

scholarly journals SnCl4-catalyzed Solvent-free Acetolysis of 2,7-Anhydrosialic Acid Derivatives

2019 ◽  
Author(s):  
Kesatebrhan Haile Asressu ◽  
Cheng-Chung Wang
Keyword(s):  
Sialic Acid ◽  
Lewis Acids ◽  
Ring Opening ◽  
Building Blocks ◽  
Solvent Free ◽  
Biologically Active ◽  
Protecting Group ◽  
Free Ring ◽  
Ring Opening Reactions ◽  
Acid Catalyzed

Sialic acid-containing glycans are found in different sialic acid forms and a variety of glycosidic linkages in biologically active glycoconjugates. Hence, the preparation of suitably protected sialyl building blocks requires high attention in order to access glycans in pure form. In this line, various C-5 substituted 2,7-anhydrosialic acid derivatives bearing both electron donating and withdrawing protecting groups were synthesized and subjected to different Lewis acid-catalyzed solvent free ring opening reactions at room temperature in the presence of acetic anhydride. Among the various Lewis acids tested, the desired acetolysized products were obtained in moderate yields under a tin(IV) chloride catalysis system. Our methodology can be extended to regioselective protecting group installation and manipulation towards a number of thiosialoside and halide donors.

Synthesis of nitrile coordinated Lewis acids Al(OC(CF3)2R)3 and their application in catalytic epoxide ring-opening reactions

2010 ◽  
Vol 384 (1-2) ◽  
pp. 171-176 ◽  
Author(s):  
Yang Li ◽  
Yi Tan ◽  
Eberhardt Herdtweck ◽  
Mirza Cokoja ◽  
Fritz E. Kühn
Keyword(s):  
Lewis Acids ◽  
Ring Opening ◽  
Epoxide Ring ◽  
Epoxide Ring Opening ◽  
Ring Opening Reactions

scholarly journals Investigations of Ring-Opening Reactions of Cyclopropanated Carbohydrates: Towards the Synthesis of the Natural Product (--)-TAN-2483B

2021 ◽  
Author(s):  
◽  
Russell James Hewitt
Keyword(s):  
Natural Product ◽  
Ring Opening ◽  
Cyclopropane Ring ◽  
Ring Expansion ◽  
Ring Opening Reactions ◽  
The Subject ◽  
The Many

<p>Cyclopropanes and carbohydrates are materials of great interest to chemists. Ring opening reactions of cyclopropanated carbohydrates have excellent potential for synthesis, due to the many diverse structures that may be obtained. The work described in this thesis explores the scope of such ring opening reactions, and extends to the synthesis and reactions of several novel cyclopropanated carbohydrates, in which synthesis of a natural product was also investigated. Several bicyclic gem-dihalocyclopropanes, including 97, were synthesised. Base-mediated cyclopropane ring opening of 97 in the presence of nucleophiles afforded a series of 2-C-branched glycosides 389 and 390 (Chapter 2), whereas silver-promoted ring expansion provided access to seven-membered rings (255 and 256) (Chapter 3). Studies on the mechanisms of the ring opening processes were also carried out. Ring-opening reactions of carbohydrate-derived gem-dihalocyclopropanes were also applied to the exploration of possible routes to the natural product (--)-TAN-2483B (154). Attempts to convert d-galactose and d-xylose into the dihydropyran 193 are the subject of Chapter 4, while the transformation of d-mannose into 193 and subsequent efforts to prepare the natural product 154 are discussed in Chapter 5.</p>

scholarly journals Investigations of Ring-Opening Reactions of Cyclopropanated Carbohydrates: Towards the Synthesis of the Natural Product (--)-TAN-2483B

2021 ◽  
Author(s):  
◽  
Russell James Hewitt
Keyword(s):  
Natural Product ◽  
Ring Opening ◽  
Cyclopropane Ring ◽  
Ring Expansion ◽  
Ring Opening Reactions ◽  
The Subject ◽  
The Many

<p>Cyclopropanes and carbohydrates are materials of great interest to chemists. Ring opening reactions of cyclopropanated carbohydrates have excellent potential for synthesis, due to the many diverse structures that may be obtained. The work described in this thesis explores the scope of such ring opening reactions, and extends to the synthesis and reactions of several novel cyclopropanated carbohydrates, in which synthesis of a natural product was also investigated. Several bicyclic gem-dihalocyclopropanes, including 97, were synthesised. Base-mediated cyclopropane ring opening of 97 in the presence of nucleophiles afforded a series of 2-C-branched glycosides 389 and 390 (Chapter 2), whereas silver-promoted ring expansion provided access to seven-membered rings (255 and 256) (Chapter 3). Studies on the mechanisms of the ring opening processes were also carried out. Ring-opening reactions of carbohydrate-derived gem-dihalocyclopropanes were also applied to the exploration of possible routes to the natural product (--)-TAN-2483B (154). Attempts to convert d-galactose and d-xylose into the dihydropyran 193 are the subject of Chapter 4, while the transformation of d-mannose into 193 and subsequent efforts to prepare the natural product 154 are discussed in Chapter 5.</p>

Asymmetric catalysis in aqueous media

2007 ◽  
Vol 79 (2) ◽  
pp. 235-245 ◽  
Author(s):  
Shū Kobayashi
Keyword(s):  
Asymmetric Catalysis ◽  
Lewis Acids ◽  
Ring Opening ◽  
Acid Catalysis ◽  
Aqueous Media ◽  
Asymmetric Reactions ◽  
Epoxide Ring ◽  
Mild Conditions ◽  
Ring Opening Reactions ◽  
Bipyridine Ligand

Lewis acid catalysis has attracted much attention in organic synthesis because of unique reactivity and selectivity attained under mild conditions. Although various kinds of Lewis acids have been developed and applied in industry, these Lewis acids must be generally used under strictly anhydrous conditions. The presence of even a small amount of water handles the reactions owing to preferential reactions of the Lewis acids with water rather than the substrates. In contrast, rare earth and other metal complexes have been found to be water-compatible. Several catalytic asymmetric reactions in aqueous media, including hydroxymethylation of silicon enolates with an aqueous solution of formaldehyde in the presence of Sc(OTf)3-chiral bipyridine ligand or Bi(OTf)3-chiral bipyridine ligand, Sc- or Bi-catalyzed asymmetric meso-epoxide ring-opening reactions with amines, and asymmetric Mannich-type reactions of silicon enolates with N-acylhydrazones in the presence of a chiral Zn catalyst have been developed. Water plays key roles in these asymmetric reactions.

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