The first bisoxazolidine ligand was prepared and applied in several asymmetric reactions. The bisoxazolidine was synthesized with high yield and high diastereoselectivity from cis-1-amino-2-indanol and 1,2-cyclohexanedione in the presence of catalytic amounts of formic acid. Bisoxazolidine-catalyzed enantioselective alkylations and alkynylations of aromatic and aliphatic aldehydes gave chiral secondary alcohols in high yields and enantiomeric excess. Moreover, this new catalyst was successfully employed in the asymmetric Henry reaction, generating β-hydroxy nitroalkanes with excellent results. Mechanistic studies of the bisoxazolidine-catalyzed reactions showed a positive nonlinear effect as a result of a unique dual phase behavior favoring enrichment of the major enantiomer in solution. It is possible that these results have important implications for the interpretation of nonlinear effects obtained under heterogeneous conditions and the origin of homochirality in nature.
Highly congested, conformationally stable 1,8-bis(3'-tert-butyl-9'-acridyl)naphthalene was prepared in 51% yield by Pd-catalyzed Stille cross-coupling of 1,8-dibromonaphthalene and 3-tert-butyl-9-tributylstannylacridine in the presence of CuO. Crystallographic studies showed that the anti-isomer exhibits a rigid structure with two cofacial acridyl rings generating a C 2-symmetric chiral pocket, which was successfully used for enantioselective sensing of a variety of chiral carboxylic acids using fluorescence spectroscopy. The sensor was used to develop into a practical method that allows determination of concentration and enantiomeric composition of chiral samples. 1,8-Bis(3'- tert-butyl-9'-acridyl)naphthalene N,N'-dioxide was found to form a highly fluorescent Sc(III) complex which was employed in a sensitive indicator-displacement assay for stereochemical analysis of chiral amino alcohols.
Finally, a highly regioselective Cu/Cu2O-catalyzed cross-coupling reaction for C-N and C-S bond formation with 2-halobenzoic acids and amines or thiols was developed. This reaction procedure gives access to anthranilic acids which have important pharmaceutical applications, and it complements existing methods, tolerates a variety of functional groups and gives high to excellent yields with a broad range of reagents.
|School Location:||United States -- District of Columbia|
|Source:||DAI-B 69/12, Dissertation Abstracts International|
|Keywords:||Asymmetric catalysis, Bisoxazolidine, Coupling, Diacridylnaphthalenes, Enantioselective sensing, Regioselective|
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