1,3-Dipolar Cycloaddition of Electron-rich Alkynes and Optically Active Allenes in Asymmetric Catalysis

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Title: 1,3-Dipolar Cycloaddition of Electron-rich Alkynes and Optically Active Allenes in Asymmetric Catalysis
Author: Qi, Xiangbing
Abstract: This dissertation includes two parts . The first part focuses on two 1 ,3 -dipolar cycloadditions of electron -rich alkynes . Chapter one describes a copper -promoted cycloaddition reaction of acetylides with diazocarbonyl compounds . This novel cycloaddition offers a direct and efficient approach to the synthesis of pyrazoles . The method is a rare example of an inverse -electron -demand cycloaddition , it represents a conceptually novel approach to this important class of heterocycles . Chapter two investigates a cycloaddition reaction between donor -acceptor cyclopropanes and silyl ynol ethers . Lewis acid promoted ring -opening of donor -acceptor cyclopropanes generates a 1 ,3 -zwitterion ; cycloaddition with a silyl ynol ether leads to a general synthesis of cyclopentenones . Substitution is tolerated on the ynol and on all positions of the cyclopropane to give tri - , tetra - , and penta -substituted cyclopentenones in high yield . methyl (methoxyl )aluminumchloride , which is generated from dimethylaluminumchloride by oxidation , appears strong reactivity towards ring -opening of donor -acceptorcyclopropanes and cycloaddition with silyl ynol ethers . This infrequently used species might be extended to other classes of cycloadditions or Lewis acid promoted reactions . The second part describes a new asymmetric catalysis design using optically active allenes as backbone and the application in an asymmetric meso -epoxides opening reaction . Allenes are inherently chiral and can be prepared in optically pure form . They have not been incorporated into ligands or catalysts for asymmetric reactions . Since allenes project functionality differently than either tetrahedral carbon or chiral biaryls , they may create complementary chiral environments . Chapter three demonstrates that optically active , C2 -symmetric allene -containing bisphosphine oxides can catalyze the addition of silicon tetrachloride to meso -epoxides with high enantioselectivity . The fact that high asymmetric induction is observed suggests that allenes may represent a new platform for the development other classes of organic catalysts or ligands for asymmetris reactions .
URI: http : / /hdl .handle .net /2152 .5 /344
Date: 2009-09-04

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1,3-Dipolar Cycloaddition of Electron-rich Alkynes and Optically Active Allenes in Asymmetric Catalysis. Graduate School of Biomedical Sciences. Available electronically from http : / /hdl .handle .net /2152 .5 /344 .

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