Dioxanones (1) are ketal- or acetal protected forms of 1,3-dihydroxyacetone (DHA). The thesis presents the stereoselective aldol transformations of dioxanones and applications to the synthesis of natural and higher carbohydrates listed in Scheme 1.<p>
The field of organocatalysis has recently gained much popularity among the chemical research community. In our group, a set of conditions are developed to perform stereoselective aldol reactions on dioxanone substrate. Cs-symmetrical dioxanones have superior diasteroselectivities than C2v-symmetrical dioxanones (de up to 88% from 34%) and presence of mild Lewis acid (LiCl) or Brønsted acid additives (PyPTS) enhance the enantioselectivity into synthetically useful ranges (from 60 up to 96 % ee).<p>
The first aldol addition of dioxanone (1) to desired aldehydes (possessing masked carbonyl functionality), followed by reduction of the corresponding aldol adduct and upon unmasking the aldehyde functionality (i.e dithiane or dimethoxy acetal hydrolysis) resulted in furanose (II) and pyranose (III) forms of D-ribose.<p>
A new protocol was developed for the synthesis of biologically important deoxyiminosugars such as L-1-deoxymannojirimycin (DMJ, IV), L-1-deoxyidonojirimycin (DIJ, V) and N-isopropyl DIJ (IV) from readily available dioxanone (1) precursor. The key steps include diastereoselective proline-catalyzed syn-aldol transformation and a reductive amination / cyclization.<p>
D-glycero-D-manno-2-octulose (VII), a higher-carbon sugar isolated from opium poppies has been synthesized in enantiomerically pure form. The short synthetic sequence involved two proline-catalyzed aldol addition reactions of dioxanone (1) to appropriate aldehydes. Here, we developed a complete dioxanone methodology towards the higher monosaccharide in a stereocontrolled fashion.<p>
The enantioselective stereodivergent first total synthesis of DD- and LL-glycero-β-alloheptopyranose (IX, ent-IX) was accomplished from readily available non-chiral starting materials. The short synthetic sequence involves enamine and enolate mediated aldol reactions at α and α' positions of dioxanone (1) hence demonstrated the complementary nature of organocatalysis and organometallic methods.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-06302010-234123 |
| Date | 02 July 2010 |
| Creators | Palyam, Nagarjuna |
| Contributors | Sawicki, Grzegorz, Majewski, Marek, Pedras, Soledade, Sanders, David A. R., Palmer, David, Green, James R. |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-06302010-234123/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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