Metal catalyzed asymmetric [2+2+1] cycloaddition reactions

Pao Yue-kong Library Electronic Theses Database

Metal catalyzed asymmetric [2+2+1] cycloaddition reactions

 

Author: Lee, Hang-wai
Title: Metal catalyzed asymmetric [2+2+1] cycloaddition reactions
Degree: M.Phil.
Year: 2008
Subject: Hong Kong Polytechnic University -- Dissertations.
Metal catalysts.
Transition metal catalysts.
Organometallic chemistry.
Ring formation (Chemistry)
Department: Dept. of Applied Biology and Chemical Technology
Pages: xii, 179 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2276222
URI: http://theses.lib.polyu.edu.hk/handle/200/5106
Abstract: Pauson-Khand-type reaction is a [2+2+1] carbonylative Cycloaddition which was firstly reported in 1971. This is one of the most powerful synthetic tools to produce cyclopentenones which are known to be versatile building blocks for natural products, pharmaceuticals and fine chemicals. Rhodium complex with chiral atropisomeric dipyidyl-diphosphine ligand, (S)-P-Phos was found to catalyze asymmetric Pauson-Khand-type reaction in aqueous medium to afford corresponding cyclopentenones in good yield and enantiomeric excess (up to 95% ee). Interestingly, a study on electronic effect of the enynes substrates revealed a correlation between the electronic property of the substrates and the ee of the cycloadducts in this reaction. A linear free energy relationship was observed from Hammett study. Besides (S)-P-Phos, (S)-BisbenzodioxanPhos was also found to be highly effective in the coorperative processes of decarbonylation of aldehyde and subsequent enantioselective Pauson-Khand-type reaction in alcoholic medium. Good yield and enantiomeric excess (up to 96% ee) of the products were obtained under these reaction conditions. Apart from rhodium metal precursor, iridium complex with (S)-BINAP was also effective in cascade decarbonylation of aldehyde and asymmetric Pauson-Khand-type reaction. Although their reactivity was inferior to rhodium catalyzed asymmetric Pauson-Khand-type reaction, they afforded the corresponding cyclopentenones with excellent enantiomeric excess (up to 98% ee), which is the highest ee achieved so far for this reaction. In addition to aldehyde as the CO source, we firstly found that formate esters were applicable as CO surrogate in Rh-catalyzed asymmetric Pauson-Khand-type reaction. Up to 94% ee cycloadducts were obtained. Microwave assisted organic syntheses have received increasing attentions in recent decades. In order to shorten the reaction time of our carbonylative cycloaddition, we applied microwave heating to our catalysis. To our delights, the asymmetric Pauson-Khand-type reaction proceeded smoothly within an hour to generate good yield of the products.

Files in this item

Files Size Format
b2276222x.pdf 4.262Mb PDF
Copyright Undertaking
As a bona fide Library user, I declare that:
  1. I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
  2. I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
  3. I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.

     

Quick Search

Browse

More Information