Applications of novel boron-nitrogen containing heterocycles : design and synthesis o planar-chiral Lewis acids for stereoselective organic synthesis

Because Lewis acids are very versatile mediators of a variety of stereoselective organic transformations, a great deal of effort has been devoted toward the development of chiral Lewis acids. This thesis describes the design, synthesis, and applications of 1,2-azaborolyl complexes as a novel family of planar-chiral Lewis acids that can perform a wide range of stereoselective transformations. The 1,2-azaborolyl ligand is a five-membered B-N bearing heterocycle that is isoelectronic and isostructural with the ubiquitous cyclopentadienyl ligand. In Part I of this dissertation, the feasibility of using boron-substituted 1,2-azaborolyls as tunable cyclopentadienyl surrogates is established. Thus, X-ray structural and spectroscopic studies demonstrate that 1,2-azaborolyls can serve as six-electron [pi]-ligands to a variety of transition metals and that the electronic nature of the boron substituent can modulate the properties of the resulting complexes. Building on the foundations of 1,2-azaborolyl ligand chemistry described in Part I, we establish in Part II that 1,2-azaborolyl complexes bearing good leaving groups on boron can serve indeed as planar-chiral Lewis acids. As a result, we have successfully synthesized a number of enantiomerically pure planar-chiral Lewis acids, and we show through structural and stereochemical correlation studies that these Lewis acids can activate substrates such as aldehydes and imines toward stereoselective nucleophilic attack in a predictable fashion. Specifically, we have investigated planar-chiral Lewis acid mediated nucleophilic attack of Grignard reagents to imines and Lewis acid mediated Mukaiyama aldol reaction of aldehydes with silyl ketene acetals.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Liu, Shih-Yuan, 1975-

Advisor dc:contributor.advisor

• Gregory C. Fu.

• Chemistry.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/30063

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/30063