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- Title
- Studies towards a catalytic asymmetric isomerization of manganese complexed alkynes to allenes using chiral bases.
- Creator
- He, Chang., Charles E. Schmidt College of Science, Department of Chemistry and Biochemistry
- Abstract/Description
-
The conversion of alkynyl carbonyls to allenyl carbonyls via manganese mediated coordination followed by a base-catalyzed isomerization was carried out using a range of chiral and achiral amine bases. Chiral amidine and chiral DBU derivatives were synthesized to carry out the isomerization enantioselectively. We employed HPLC equipped with a chiral column to determine the enantiomeric excess. We also proved that the mechanism of that the manganese-coordinated alkyne/allene rearrangement...
Show moreThe conversion of alkynyl carbonyls to allenyl carbonyls via manganese mediated coordination followed by a base-catalyzed isomerization was carried out using a range of chiral and achiral amine bases. Chiral amidine and chiral DBU derivatives were synthesized to carry out the isomerization enantioselectively. We employed HPLC equipped with a chiral column to determine the enantiomeric excess. We also proved that the mechanism of that the manganese-coordinated alkyne/allene rearrangement reaction involved an intermediate cumenolate. It was also confirmed that amine base with pKa lower than that of DBU (pKa = 13.6) would not carry out the isomerization. Alkoxy base were also used in isomerization and the mechanism was also investigated.
Show less - Date Issued
- 2009
- PURL
- http://purl.flvc.org/FAU/192983
- Subject Headings
- Enzyme kinetics, Organometallic compounds, Synthesis, Asymmetric synthesis, Methathesis (Chemistry), Carbonyl compounds, Synthesis
- Format
- Document (PDF)
- Title
- Catalytic Asymmetric Isomerizations of Alkynes To Allenes And Their Diastereoselective Functionalization Facilitated By An Organomanganese Auxiliary.
- Creator
- Roy, Animesh, Lepore, Salvatore D., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Chemistry and Biochemistry
- Abstract/Description
-
The present dissertation research is largely focused on the methods to synthesize highly substituted allene derivatives from alkynes in conjugation with carbonyl-containing functional groups. A key aspect of this research involves methylcyclopentadienylmanganese dicarbonyl (MMD), an inexpensive and air-stable organometallic auxiliary linked to alkynyl carbonyls via an η2-bond. This auxiliary influences bond formation to achieve enhanced stereoselectivity without itself undergoing any chemical...
Show moreThe present dissertation research is largely focused on the methods to synthesize highly substituted allene derivatives from alkynes in conjugation with carbonyl-containing functional groups. A key aspect of this research involves methylcyclopentadienylmanganese dicarbonyl (MMD), an inexpensive and air-stable organometallic auxiliary linked to alkynyl carbonyls via an η2-bond. This auxiliary influences bond formation to achieve enhanced stereoselectivity without itself undergoing any chemical transformation. Chapter 1 accounts various examples of such transition metal auxiliaries including MMD. Typically conjugated alkynyl carbonyls do not isomerize to thermodynamically less favored allenes. However, with the MMD auxiliary in place, alkynyl carbonyl compounds undergo facile 1,3-proton shifts in the presence of a mild base to produce allene isomers. Although allenyl aldehydes are important building blocks, we note that direct methods to prepare them nonracemically are not known. Chapter 2 describes the development of a new cinchonine-based phase transfer catalyst to access non-racemic allenyl aldehydes from MMD-complexed alkynyl aldehydes. With the manganese auxiliary in place, nonracemic allenyl aldehydes were obtained in a weakly basic biphasic reaction system via enantioselective protonation conditions. Chapter 3 describes the second use of the MMD auxiliary to direct nucleophilic addition reactions to allenyl aldehydes for the preparation of 2,3-allenols diastereoselectively. In the absence of the MMD auxiliary, nucleophilic reactions to the carbonyl group of axially chiral allenyl aldehydes is poorly diastereoselective, which is a long-standing problem. We observed that, in addition to leading to non-racemic allenyl aldehydes, the MMD auxiliary could also be used to improve diastereoselectivity in carbonyl additions due to its proximal position on the 2,3-bond of the allenyl aldehyde. Chapter 4 describes the use of allenyl esters as metathesis quenching agents. It was observed that the addition of an allenyl ester after a metathesis reaction was complete; facilitate the removal of most ruthenium metal impurities using simple silica chromatographic purification.
Show less - Date Issued
- 2017
- PURL
- http://purl.flvc.org/fau/fd/FA00004918
- Subject Headings
- Transition metal catalysts., Stereochemistry., Chemistry, Organic., Chemistry, Physical and theoretical., Asymmetric synthesis.
- Format
- Document (PDF)