Polymer-supported reagents and catalysts, which allow for simple product
separation and easy recycling, have been widely studied in the context of organic
synthesis. The past decade has witnessed a number of new variations of
polymeric materials, and among the most frequently immobilized functionalities
are amines that possess versatile synthetic utilities.
Polymers with new structures and improved properties for use in synthesis
have been continuously developed since the support may impact the chemical
reactions in which they are used in various ways. A new heterogeneous
polystyrene-based amine, rasta resin-DMAP, has been synthesized and used in
addition reactions of carbon dioxide to epoxides to afford cyclic carbonate
products. This new material was found to be a more efficient catalyst than
divinylbenzene cross-linked polystyrene supported DMAP, and was readily
recycled without significant loss of catalytic activity.
Compared to polymers bearing a single functionality, polymers possessing
multiple different functional groups attached to a single polymer backbone would
have greater potential utility, especially in reactions requiring multiple catalysts or
reagents. As an example of this concept, a bifunctional polystyrene bearing both
DMAP and piperazine groups has been prepared and applied as an organocatalyst
for decarboxylative Doebner-Knoevenagel reactions of arylaldehydes and
mono-ethyl malonate to produce (E)-,-unsaturated esters in high yields.
Additionally, both non-cross-linked and cross-linked bifunctional polystyrenes
featuring amine and thiourea groups have been developed, and their catalytic
performance were evaluated in reactions of nitroalkenes with either nitroalkanes
or sulfur ylides. Both polymers proved to be efficient catalysts in these reactions
and the insoluble polymer demonstrated high recyclability. Control experiments
using monofunctional polymers indicated that both catalytic groups of these
bifunctional polymers are essential and they could work cooperatively to achieve
efficient catalysis.
Finally, a second generation bifunctional phosphine-amine polymer, rasta
resin-PPh3-NBniPr2, was prepared and examined in tandem Wittig-reductive aldol
reactions. In these reaction cascades, the phosphine oxide groups generated
from the Wittig reaction served as the catalyst for the reductive aldol reaction, and
moderate yields of structurally diverse -hydroxy ketones could be obtained from
one-pot processes involving 5 sequential reactions. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/180062 |
| Date | January 2011 |
| Creators | Lu, Jinni., 陆今妮. |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B4775252X |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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