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91.
Rahul B. Kawthekar Sai Kumar Chakka Vivian Francis Pher G. Andersson Hendrik G. Kruger Glenn E.M. Maguire Thavendran Govender 《Tetrahedron: Asymmetry》2010,21(7):846-852
A novel family of eleven new tetrahydroisoquinoline (TIQ)–oxazoline intermediates and five corresponding copper(II) catalysts has been developed and applied to the catalytic asymmetric Henry reaction of various aldehydes with nitromethane to provide β-hydroxy nitroalkanes in high conversion (>99%). This paper describes the synthesis of the TIQ compounds from l-dihydroxyphenylalanine (l-DOPA) as the starting material. The chiral ligands were complexed in situ with various transition metals such as Cu, Sc, Co, Zn, Ni and Mn and tested as a chiral catalyst for the Henry reaction. The reaction was optimized in terms of the metal, counter ion, solvent, temperature and over a range of substrates. The corresponding catalyst with copper(II) acetate and 2-propanol as the solvent provides the best enantioselectivities (up to 77% ee) of the corresponding nitroalcohol for 4-chlorobenzaldehyde. 相似文献
92.
93.
Byron K. Peters Sai Kumar Chakka Tricia Naicker Glenn E.M. Maguire Hendrik G. Kruger Pher G. Andersson Thavendran Govender 《Tetrahedron: Asymmetry》2010,21(6):679-687
The use of the tetrahydroisoquinoline scaffold is well documented in biologically active compounds. However, reports of the utilisation of tetrahydroisoquinoline compounds in asymmetric catalysis are limited. The synthesis of novel diamine ligands possessing the tetrahydroisoquinoline (tetrahydroisoquinoline) backbone and evaluation of their activity in the asymmetric transfer hydrogenation of acetophenone are presented. The diamine ligands in conjunction with i-PrOH as the hydrogen source and [RhCl2(Cp1)]2 as the metal precursor proved to be the most effective of the tetrahydroisoquinoline derivatives for this catalytic system. Water was found to have a profound influence on the enantioselectivity of the reaction. Optimisation of the amount water, i-PrOH and catalytic loading content rendered the best result of 70% enantioselectivity for the (S)-1-phenylethanol isomer product. 相似文献
94.
95.
We consider principal pivot transform (pivot) on graphs. We define a natural variant of this operation, called dual pivot, and show that both the kernel and the set of maximally applicable pivots of a graph are invariant under this operation. The result is motivated by and applicable to the theory of gene assembly in ciliates. 相似文献
96.
Oluseye K. Onajole Patrick Govender Thavendran Govender Glenn E. M. Maguire Hendrik G. Kruger 《Structural chemistry》2010,21(6):1203-1209
The NMR elucidation of five novel SQ109 analogues including SQ109 is reported herein. These derivatives were synthesized as
potential anti-tuberculosis candidates. One-dimensional NMR (1H and 13C) techniques show a series of overlapping signals from the methine and methylene groups of these compounds, thereby making
it extremely difficult to assign all NMR signals. Two-dimensional (2D) NMR techniques were instrumental in overcoming these
challenges. This paper appears to be a rare report on the complete structure elucidation of mono-substituted adamantane moieties. 相似文献
97.
Oluseye K. Onajole Maya M. Makatini Patrick Govender Thavendran Govender Glenn E. M. Maguire Hendrik G. Kruger 《Magnetic resonance in chemistry : MRC》2010,48(3):249-255
The synthesis and complete NMR elucidation of eight novel pentacycloundecane (PCU) derivatives are reported. These compounds are precursors in the synthesis of PCU‐based anti‐tuberculosis (TB) agents and potential human immunodeficiency virus (HIV) protease inhibitors. Two‐dimensional (2D) NMR techniques were used to assign the NMR spectra for these compounds. Substitution of the cage molecule at (C‐8/11) further complicates the assignment, since some of the substituted alkyl chain groups overlap with the cage proton signals. The side chain heteroatoms also introduce a rare through‐space deshielding effect to some of the carbon atoms of the cage skeleton. Ring strain in the rigid cage skeleton appears to induce drastic electronic changes in some parts of the cage framework. This observation is more dramatic for the C‐4 methylene group of the cage diols and the cage ethers. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
98.
We investigate the derived structures of compact polygons at half-regular and at regular points. This enables us to give a geometric characterization of the real or complex split Cayley hexagon. 相似文献
99.
Hendrik De Bie 《Physics letters. A》2008,372(24):4350-4352
A superspace version of the Schrödinger equation with a delta potential is studied using Fourier analysis. An explicit expression for the energy of the single bound state is found as a function of the super-dimension M in case M is smaller than or equal to 1. In the case when there is one commuting and 2n anti-commuting variables also the wave function is given explicitly. 相似文献
100.
In this paper, we prove that the Hermitian quadrangle is the unique generalized quadrangle Γ of order (q
2, q
3) containing some subquadrangle of order (q
2, q) isomorphic to such that every central elation of the subquadrangle is induced by a collineation of Γ.
Dedicated to Dan Hughes on the occasion of his 80th birthday. 相似文献