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Synthesis of novel N, P-ligands and their appliation in asymmetric catalysis
Title:
Synthesis of novel N, P-ligands and their appliation in asymmetric catalysis
Author:
Hand, John Bernard, author.
ISBN:
9780438059641
Personal Author:
Physical Description:
1 electronic resource (180 pages)
General Note:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: Pavel Kocovsky.
Abstract:
Morimoto recently applied NP-ligands 44 and 45 to the enantioselective copper-catalysed conjugate addition of diethylzinc to 2-cyclohexen-1-one la, achieving enantioselectivity ≤52% ee. Assuming that the coordination to the metal occurs through the pyridine and phosphine groups, it would result in the formation of an eight-membered ring. The single chiral centre in this complex is rather distant from the metal to be able to effectively influence the new bond-forming process occurring at the metal. As a result, low enantioselectivity was attained. It was reasoned that introduction of an additional alkyl group (relay group) at the amide nitrogen should add more bias to the chelate by forcing the side-chain of the amino acid backbone and the N-alkyl group away from each other. The resulting arrangement should create an appropriate conformational twist about the carbonyl-pyridine bond, thereby creating a chiral axis. In this way, the chiral information from the amino acid backbone would be relayed to the metal. To verify this hypothesis, several analogous ligands incorporating a chiral relay group were synthesised and employed in the catalysed conjugate addition of diethylzinc to cyclic and acyclic enones under optimised experimental conditions. It has been demonstrated that the tertiary amide group in new amino acid-based ligands can relay the chiral information to the metal coordinated. It controls the level and the sense of asymmetric induction in the copper-catalysed conjugate addition of diethylzinc to enones with ≤ 87% ee. The highest enantioselectivity obtained during the research campaign was 91% ee in the copper catalysed conjugate addition of diethylzinc to chalcone employing ligand (S)-(+)-77. The nature of the pyridine moiety in the ligands was found to have a significant impact on enantioselectivity. Spectroscopic investigationcombined with a non-linearity study indicates a monomeric copper chelate which aggregates in solution to be the likely active catalyst. Limited success was achieved applying the chiral relay ligand to other catalytic asymmetric reactions. The ligands were found to be ineffective for the silver-catalysed asymmetric [3 + 2] cycloaddition of azomethine ylides. Promising preliminary results for the copper-catalysed addition of diethylzinc to activated imines substrates were obtained. N-benzylidene-4-methyl-benzenesulfonamide was obtained in 64% ee, however further efforts did not improve the enantioselectivity.
Local Note:
School code: 0547
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Shelf Number | Item Barcode | Shelf Location | Status |
|---|---|---|---|
| XX(684741.1) | 684741-1001 | Proquest E-Thesis Collection | Searching... |
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