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http://hdl.handle.net/11375/21435
Title: | New Applications of Phosphonium Salts in Organic synthesis |
Authors: | Huang, Ying |
Advisor: | McNulty, James |
Department: | Chemistry |
Keywords: | Phosphonium Salts;Organic synthesis;Wittig olefination;allylic trialkylphosphorus |
Publication Date: | Apr-2005 |
Abstract: | <p> This thesis describes the development of the Wittig olefination reaction of stabilized, semistabilized allylic trialkylphosphorus ylides with various aldehydes to afford E olefins mainly (E>89%). Since the steric demand of trialkylphosphorus ylides was decreased, aldehydes achieved high E selectivity. On the other hand, predominant or exclusive formation of Z olefms was achieved by using allylic triphenylphosphorus ylides and aromatic aldehydes like benzylaldehyde, while the combination of allylic triphenylphosphorus ylides and such sterically hindered aldehydes as cyclohexanecarboxaldehyde led to E olefm formation upon ylide formation with LiHMDS. In the case of olefination reactions of aldehydes with dimethyl thiazole ylide, it was shown that among the aromatic aldehydes only 4-nitrobenzaldehyde reacted with this ylide and provided a pure E olefin product (41% yield). Dimethylmalonyltributylphosphorane (DMTP) reacted with aromatic aldehydes in toluene at 125 °C to give the corresponding alkenes. 4-Nitrobenzaldehyde· gave the alkene in a much higher yield (81%), followed by 4-chlorobenzaldehyde (31%). With benzaldehyde, the corresponding olefin was isolated in only 14% yield under these conditions. Clearly, this highly stabilized ylide only enters into reaction with electron deficient aldehydes. A possible approach to Z-a, P-unsaturated aldehydes was investigated through the olefination of an acetal-ylide followed by hydrolysis. However, E acetal olefins were in fact isolated from this 2'-(1,3-dioxolanyl)-triethylphosphorus ylide with aromatic aldehydes in good yields (62%-76%). This result is still mechanistically interesting in view of the chemoselective formation of such an ylide in the presence ofthree ethyl substituents on phosphorus. </p> <p> Class of flavonoids: Sakuranetin, Naringenin and (28)-7-methoxy-6hydroxyflavanone, have been isolated from the diseased bark of Prunus sp. The structures were elucidated based on the spectroscopic data. Locations of 4-keto, 5-0H and 7-methoxy were deduced from COSY and HMBC spectra. Such compounds are of interest for their potential antibiotic activity against vancomycin-resistant strains of microbes. </p> |
URI: | http://hdl.handle.net/11375/21435 |
Appears in Collections: | Digitized Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Huang_Ying_2005Apr_Masters.pdf | 2.29 MB | Adobe PDF | View/Open |
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