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Journal ArticleDOI

A short and convenient way to produce the Taxol A-ring utilizing the Shapiro reaction

TL;DR: In this paper, a Taxol A-ring building block was converted in three simple steps to various arenesulfonylhydrazones and then to the target molecule with the Shapiro reaction.
About: This article is published in Tetrahedron.The article was published on 2002-03-11 and is currently open access. It has received 27 citations till now. The article focuses on the topics: Shapiro reaction.

Summary (1 min read)

1. Introduction

  • The authors have earlier reported their entries to the side chain 2 6 and the C-ring precursor 4.
  • The use of intramolecular electrophiles allows preparation of cyclic products with high stereoselectivity.
  • The route involves only four steps and proceeds with high yields.

2. Results and discussion

  • Methylation (13a!14a) was incomplete in these experiments.
  • Also, TMEDA/hexane was impracticable here because of strong salt formation between CH 3 I and TMEDA.

3. Conclusions

  • Taxole A-ring building block 10 was synthesized with a novel and short method consisting of only four steps with high 38% overall yield.
  • Tosylhydrazone 9a was found to be the best of the studied arylhydrazones in Shapiro reaction allowing the formation of stable dianions and complete methylation.
  • Evidence of the possible effect of steric hindrance was observed in the preparation and reactivity of hydrazones.
  • Protonation of the vinyl anion by THF remained problematic to some extent giving always some protonated vinyl anion.
  • This can be minimized with rapid decomposition of dianion 15a at room temperature followed by immediate addition of the electrophile.

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Citations
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Journal ArticleDOI
TL;DR: This review covers the literature from the discovery of the first taiwaniaquinoid in 1995 until June 2009 and a detailed discussion of 12 published syntheses of members of this family of natural products is presented.
Abstract: A comprehensive overview of the taiwaniaquinoid family of natural products is presented. A summary of the isolation, biosynthesis, and biological activity of these compounds is followed by a discussion of various synthetic strategies to the skeletal framework and a detailed discussion of 12 published syntheses of members of this family. This review covers the literature from the discovery of the first taiwaniaquinoid in 1995 until June 2009.

115 citations

Journal ArticleDOI
TL;DR: A combination of X-ray crystallographic data, deuterium labeling, and chemical correlation studies provides further evidence as to the correct absolute stereochemical assignment of (+)-frondosin B.
Abstract: The frondosins are a family of marine sesquiterpenes isolated from the sponge Dysidea frondosa that exhibit biological activities ranging from anti-inflammatory properties to potential application in anticancer and HIV therapy. Herein, a concise enantioselective total synthesis of (+)-frondosin B is described which requires a total of three chemical steps. The enantioselective conjugate addition of a benzofuran-derived boronic acid to crotonaldehyde in the presence of an imidazolidinone organocatalyst builds the critical stereogenic center of frondosin B in the first operation, while the remaining two ring systems of this natural product are installed in the two subsequent steps. A combination of X-ray crystallographic data, deuterium labeling, and chemical correlation studies provides further evidence as to the correct absolute stereochemical assignment of (+)-frondosin B.

77 citations

Journal ArticleDOI
TL;DR: The spirooxindole ring system of citrinadin A has been synthesized with excellent control over the absolute stereochemistry at the spirocenter using a novel diastereoselective DMDO-mediated oxidative rearrangement employing an 8-phenylmenthol chiral auxiliary on the indole nitrogen.

66 citations

Journal ArticleDOI
TL;DR: In this article, a series of Ru-based olefin metathesis catalysts containing N,N′-diamidocarbenes (DACs) were synthesized and studied.

58 citations

Journal ArticleDOI
TL;DR: A convergent synthesis of the ABC ring of antitumor natural product paclitaxel (Taxol) is described and SmI2-mediated reductive cyclization of an allylic benzoate possessing an aldehyde function is described.

39 citations

References
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01 Jun 1977
TL;DR: Localized Chemical bonding Delocalized Chemical Bonding Bonding Weaker than Covalent Stereochemistry Carbocations, Carbanions, Free Radicals, Carbenes and Nitrenes Mechanisms and Methods of Determining them Photochemistry Acids and Bases Effects of Structure on Reactivity Aliphatic Nucleophilic Substitution Aromatic Electrophilic Substitutes Aliphatically Electrophilic Substitution Free-Radical Substitution Addition to Carbon-Carbon Multiple Bonds Adding to Carbon Hetero Multiple Bonds Eliminations Rearrangements Ox
Abstract: Localized Chemical bonding Delocalized Chemical Bonding Bonding Weaker than Covalent Stereochemistry Carbocations, Carbanions, Free Radicals, Carbenes and Nitrenes Mechanisms and Methods of Determining Them Photochemistry Acids and Bases Effects of Structure on Reactivity Aliphatic Nucleophilic Substitution Aromatic Electrophilic Substitution Aliphatic Electrophilic Substitution Free-Radical Substitution Addition to Carbon-Carbon Multiple Bonds Addition to Carbon- Hetero Multiple Bonds Eliminations Rearrangements Oxidations and Reductions The Literature of Organic Chemistry Classifications of Reactions by Type of Compound Synthesized.

4,885 citations

Journal ArticleDOI
TL;DR: This account attempts to bring together in a cogent overview the chemistry and biology of taxol, one of the few organic compounds, which, like benzene and aspirin, is recognizable by name to the average citizen.
Abstract: One can view plants as a reference library of compounds waiting to be searched by a chemist who is looking for a particular property. Taxol, a complex polyoxygenated diterpene isolated from the Pacific Yew, Taxus brevifolia, was discovered during extensive screening of plant materials for antineoplastic agents during the late 1960s. Over the last two decades, interest in and research related to taxol has slowly grown to the point that the popular press now seems poised to scoop each new development. What was once an obscure compound, of interest only to the most masochistic of synthetic chemists and an equally small number of cellular biologists, has become one of the few organic compounds, which, like benzene and aspirin, is recognizable by name to the average citizen. In parallel, the scientific study of taxol has blossomed. Physicians are currently studying its effects on nearly every known neoplasm. Biologists are using taxol to study the mechanisms of cell function by observing the effects of its interactions with the cellular skeletal systems. Synthetic chemists, absorbed by the molecule's unique and sensitive structure and functionality, are exploring seemingly every available pathway for its synthesis. Indeed, the demand for taxol has risen so in the last five years that alternative sources to the extraction of T. brevifolia are being vigorously pursued. Because of the rapidly expanding scope of research in the multifaceted study of taxol, those who are interested in the field may find acquisition of a reasonable base of knowledge an arduous task. For this reason, this account attempts to bring together, for the first time, in a cogent overview the chemistry and biology of this unique molecule.

554 citations

Journal ArticleDOI
TL;DR: The chemistry of the potent anticancer diterpenoid taxol is reviewed, with an emphasis on isolation and analysis, structural modifications, partial synthesis, and structure-activity relationships.

275 citations

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