During this project, we reached the aim of establishing synthetic routes to new hydroxamic acid derivatives, which were used as ligands for asymmetric epoxidation of allylic alcohols in water. Three new ligands, (S, R)-3, (S, S)-3 and 14 were successfully synthesized and subsequently tested on standard substrates. To accomplish the ligand synthesis, we used known procedures as well as new ones, for example the coupling of in situ-protected hydroxylamine 5a and activated mixed anhydride 13. As yields were not always satisfying (see Experimental), optimization of several steps could be a general aim for future work, especially considering the synthesis up-scaling of promising ligand 14.
Table of Contents
1 Introduction
1.1 Sharpless Epoxidation
1.2 Yamamoto-Malkov Epoxidation
1.3 Camphor Derivatives
1.4 Phosphinamides
1.5 Sulfinamides
2 Project Objective
3 Results and Discussion
3.1 Camphor-derived hydroxamic acids
3.1.1 Synthesis of ligands 3
3.1.2 Application of ligand 3 to vanadium-catalyzed epoxidation
3.2 Hydroxamic acid based on diphenylphosphinamide moiety
3.2.1 Synthesis of ligand 14
3.2.2 Application of ligand 14 to vanadium-catalyzed epoxidation
3.3 Hydroxamic acids containing sulfinamide moiety
3.3.1 Synthesis of ligand 19 using direct method
3.3.2 Synthesis of ligand 19 using Nosyl protecting group
3.4 Synthesis of N-Benzhydryl-hydroxylamine 5
4 Conclusions and Future Aspects
4.1 General
4.2 Camphor derivatives
4.3 Sulfinamides
4.4 Phosphinamides
4.5 Anilides
4.6 Binaphthyls
5 Experimental
5.1 General Methods
5.2 Synthesis of hydroxylamine
5.3 Synthesis of Camphor-derived hydroxamic acids
5.3.1 Sulfonamides
5.3.2 Acid chlorides
5.3.3 Hydroxamic acids
5.4 Synthesis of Dpp-derived hydroxamic acid
5.5 Synthesis of sulfinamide-derived amino acid
5.6 Synthesis of N-Nosyl-(R)-phenylglycine
5.7 Epoxidation in water
6 References
Objectives and Topics
This project aims to synthesize three new classes of ligands to influence the product formation in vanadium(V)-catalyzed asymmetric epoxidation in water. By preserving the amino acid backbone and benzhydryl-amino moieties, the research explores how varying amide nitrogen substituents impacts reaction selectivity and reactivity.
- Synthesis of camphor-derived hydroxamic acids
- Development of diphenylphosphinamide-based ligands
- Research into sulfinamide-containing hydroxamic acids
- Optimization of ligand performance in aqueous epoxidation
- Exploration of future potential ligand scaffolds
Excerpt from the book
3.1 Camphor-derived hydroxamic acids
The use of chiral camphor moiety is the reasonable continuation of the strategy that introduces ligand chirality by modifying the amino acid backbone. Enhancing the, so far non-chiral, sulfonamide moiety by addition of a stereogenic centre should enable the ligand (Figure 7) to influence the stereochemistry of asymmetric epoxidation in a way to reach higher enantiomeric excess. Also, the bulky quality of the bicyclic scaffold is supposed to influence the selectivity of product formation. Furthermore, the sulfonamide moiety is stable against strong acids and bases, and therefore easy to handle and useful substrates can be build even under harsh reaction conditions.
Synthesis of each diastereomer (S, R)-3 and (S, S)-3 was accomplished in four convergent steps (Scheme 3). Starting from enantiopure (S)- or (R)-phenylglycine, which were coupled under aqueous conditions with commercially available (1S)-Camphor-10-sulfonic acid chloride to sulfonamides 1, the synthesis was continued by using phosphorus pentachloride in anhydrous ether to obtain acid chlorides 2.
To prevent the possible O-acylation in the next step, hydroxylamine 5 was protected in situ with chlorotrimethylsilane in presence of 2,6-lutidine, which acted as a non-nucleophilic base.
The subsequent coupling with 2, carried out in anhydrous THF, and O-deprotection with water furnished camphor-derived hydroxamic acids 3 in 44 – 73% yield.
Summary of Chapters
1 Introduction: Provides an overview of asymmetric epoxidation, including historical methods and current research into various ligand classes.
2 Project Objective: Outlines the goal of synthesizing new ligand classes to improve vanadium-catalyzed epoxidation in water.
3 Results and Discussion: Details the synthetic pathways for camphor-derived, phosphinamide-based, and sulfinamide-based ligands, along with their testing in epoxidation reactions.
4 Conclusions and Future Aspects: Summarizes the performance of the developed ligands and proposes directions for future research into new scaffolds.
5 Experimental: Describes the specific chemical methodologies, reagents, and analytical data for all synthesized compounds.
6 References: Lists the academic literature and protocols cited throughout the report.
Keywords
Asymmetric epoxidation, Vanadium catalysis, Hydroxamic acids, Camphor derivatives, Phosphinamides, Sulfinamides, Ligand synthesis, Allylic alcohols, Enantioselectivity, Aqueous systems, Phenylglycine, N-Benzhydryl-hydroxylamine, Stereogenicity, Catalyst loading, Chemical synthesis
Frequently Asked Questions
What is the primary focus of this research report?
The report focuses on the synthesis and testing of novel hydroxamic acid-derived ligands for use in vanadium-catalyzed asymmetric epoxidation reactions performed in water.
What are the central themes of the work?
The work centers on modifying chiral building blocks—specifically camphor, phosphinamides, and sulfinamides—to improve the stereoselectivity of epoxidation reactions.
What is the primary objective of the project?
The primary objective is to develop new classes of ligands that retain successful backbone features (like amino acid and benzhydryl-amino groups) while testing different substituents on the amide nitrogen to influence reaction outcomes.
Which scientific methodology is primarily employed?
The research uses organic synthesis methodologies to create ligands, followed by catalytic epoxidation trials, with characterization via NMR spectroscopy, chiral gas chromatography, and high-resolution mass spectrometry.
What does the main body of the document cover?
The main body details the step-by-step synthetic routes for ligand development, the specific conditions used for vanadium-catalyzed epoxidation in aqueous media, and the analytical results from these trials.
Which keywords best describe this study?
The study is best characterized by terms such as asymmetric epoxidation, vanadium catalysis, ligand synthesis, and hydroxamic acids.
Why was the camphor moiety incorporated into the ligands?
The camphor moiety was used as a bulky, chiral bicyclic scaffold to introduce additional chirality into the ligand backbone in an effort to achieve higher enantiomeric excess during the epoxidation process.
Why did the researchers decide to investigate phosphinamide-based ligands?
The researchers investigated phosphinamides to amplify the sterical extent of the amide moiety, aiming to improve enantioselectivity compared to standard sulfonamide ligands.
What challenges were encountered during the synthesis of sulfinamide-based ligands?
The team faced significant difficulties related to the acid lability of the S-N bond and the poor solubility properties of the intermediates, which ultimately hampered the isolation of the target ligands.
What is the significance of the phosphinamide-derived hydroxamic acids?
This report represents the first application of phosphinamide-derived hydroxamic acids in the context of vanadium-catalyzed asymmetric epoxidations in water, establishing a baseline for future optimization.
- Citar trabajo
- Dominik Ohlmann (Autor), 2007, Novel Hydroxamic Acid-Derived Ligands for Vanadium Catalysed Asymmetric Epoxidations, Múnich, GRIN Verlag, https://www.grin.com/document/463480
