Chiral Spirodiphosphine Dioxides Organocatalysis and Hydrogen Transfer Reduction

This dissertation, "Chiral Spirodiphosphine Dioxides Organocatalysis and Hydrogen Transfer Reduction" by Jiawen, Guo, 郭嘉雯, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Recently, during the past10 years, with the intensified attention paid to the environment and industrial development, there has been growing interest in organocatalysis. One important area of the organocatalysis is the development of new designs of chiral catalysts for the synthesis of optically pure products. Another important area is to develop methods to simplify the purification of multi-component reactions. A chiral spirobiindane-based bisphosphine oxide catalyst was synthesized and employed in various reactions including Abramov-type phosphonylation reactions, reductive aldol reactions, direct aldol reactions, allylations, reductive cyclizations and C=N reduction reactions. The rigid and axially chiral spirobiindane skeleton of the bisphosphine oxide introduces steric hindrance and results in moderate to good enantioselectivity in Abramov phosphonylation and reductive cyclization reactions. However, the great steric hindrance of the catalyst also imposes negative effects on catalyst activity and yields of reactions. The observed slow reaction rates may possibly have led to the undesired, non-selective background reactions and therefore a lowered enantioselectivity. Secondly, the success of polymer-supported reagents in facilitating product purification prompted our attempt to prepare and examine two different types of polymer-supported benzothiazolines for hydrogen transfer reduction. An in situ generated self-supported polybenzothiazoline proved to be a rapidly formed polymer under mild conditions and could be applied to hydrogenation transfer reduction reactions with active alkenes. A rasta resin-supported benzothiazoline was also synthesized and examined in similar transformations. Both of the two polymer reagents afforded the desired reduction products, but further optimizations may be required to suppress the formation of byproducts and to improve their reactivity. DOI: 10.5353/th_b5153730 Subjects: Catalysts - Synthesis Catalysis Chemistry, Organic