PART I: SYNTHESIS AND APPLICATION OF CYCLOPENTADIENONESPART II: BIFUNCTIONAL ORGANOCATALYSTS
Abstract
by
YAN ZHOU
Cyclopentadienones have a high potential for organic synthesis. Cyclopentadienones can be formed by cyclocarbonylation of alkynes. After a pioneering work of CpCo(PPh3)2-mediated alkyne-alkyne coupling, RhCl(PPh3)3-, Cp(Co(CO)2-, Fe(CO)5-, and IrCl(CO)(PPh3)2-mediated alkyne-alkyne couplings were reported for the synthesis of cyclopentadienones. But most of these procedures require harsh conditions, such as high temperature (>120°C) and high pressure of carbon monoxide. Therefore, for those thermally unstable substrates, these methods show low yields. The objective of this project is to find new transition metal catalysts, which can promote cyclocarbonylation of alkynes to form cyclopentadienones more efficiently and practically. Molybdenum carbonyl complexes show good activity in Pauson-Khand reactions. Encouraged by these results, molybdenum carbonyl complexes were examined in cyclocarbonylation of alkynes. However it was found that disappointing yields were obtained in most cases.
Among reactions of cyclopentadienones, Diels-Alder reactions are the most extensively studied. Cyclopentadienones can react as dienes in Diels-Alder reactions with dienophiles. Previous work in our laboratory has shown that monocyclic cyclopentadienones, which are obtained from silicon tethered Fe(CO)5-promoted cyclocarbonylation of alkynes, are good candidates for preparing aromatic and biaryl structures via Diels-Alder type reactions and subsequent thermal decarbonylation. In this study, we have evaluated and expanded Diels-Alder applications on cyclopentadienones. The biaryl structures formed by this methodology could find use as intermediates in the synthesis of complex molecules.
A new trend in organocatalyst design is to develop catalysts possessing two or more reaction promoting functionalities. Development of these organocatalysts is of ongoing interest in asymmetric synthesis. In Part II, new acid-base bifunctional organocatalysts are designed for asymmetric reactions, such as aldol reaction, Michael addition, Morita-Baylis-Hillman reaction, Mannich reaction and so on. Preliminary results are reported for the synthesis of the potential catalysts.