Asymmetric Gold-Catalyzed Cycloaddition Reactions Involving Acetylene Fragments

The main work of the thesis is around gold-catalyzed asymmetric cycloaddition reactions, which is devided into two parts and is listed as follows:In the first part, gold-catalyzed asymmetric [3+3] cycloaddition reactions of conjugated eneyne ketones with nitrones are discussed. A series of furan and oxazoline bicyclic fused compounds were obtained with high yield, high diastereo selectivity and high enantioselectivity. It is found that excellent results can be achived by modification substituted groups connecting to phosphorus or changing the dugedrak angle of chiral ligand MeO-biphep.The catalyst loading could be reduced to0.2mol%without any loss in the yield, diastereoselectivity and enantioselectivity on-a5mmol scale reaction.The adduct could undergo further chemoselective transformation to give the isolated optically active multi-functionalized furan in good yield without loss of ee from the Pd/C-catalyzed hydrogenation.The second part focuses on the gold-catlayzed asymmetric [3+2] cycloaddition reactions of y-alcohol-butyne acid ester acetal with aromatic aldehydes (ketones) derivatives. The reactions gave a class of functional4-alkoxy2,5-dihydrofuran, a key unit in some natural products and drug molecules, with high yields and excellent enantioselectivites under mild conditions. In the same time, a series of phosphoramide ligands, which were designed and synthesized, have been successfully used in the reaction. Like in the case of the first part, catalyst loading could be reduced to1mol%with a larger reaction scale (5mmol) without loss of any selectivity and efficiency to provide the product. This method provides a simple and effective route to synthesis this kind of compounds. By introducing the optical pure substrate, the reaction mechanism was also investigated, which indicated that a all-carbon1,3-dipole was involved in the reaction.