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作者 Phuan, Puay-Wah
書名 Novel ligands for asymmetric reactions: Development of biconformational diamines as chemo-responsive molecular switches
國際標準書號 0496567535
book jacket
說明 299 p
附註 Source: Dissertation Abstracts International, Volume: 64-10, Section: B, page: 4948
Supervisor: Marisa C. Kozlowski
Thesis (Ph.D.)--University of Pennsylvania, 2003
The work described in this dissertation encompassess two major areas of research. The first part centers on explorations of novel gamma-aminoalcohol and diamine ligands for asymmetric reactions. cis-Decalin gamma-aminoalcohols 1 and 2 along with constrained analogues were identified a computer-aided ligand design program, and were synthesized and examined in the asymmetric organozinc additions to benzaldehyde. The selectivities of these ligands were low to moderate. Theoretical studies of the transition structures were done to understand the origin of the enantioselectivities.*
The simplest chiral portion of sparteine, which is bispidine 18 , was prepared and was found to exhibit moderate enantioselectivity as a ligand in the asymmetric lithiation-substitution reaction of N-Boc pyrrolidine. Theoretical studies of the transition structures indicate that 18 should be far less selective than sparteine. Thus, the important stereochemical features of sparteine have been definitively established.*
The second area of research is in the study of the conformational switch of aza-cis-decalins, such as 33, and 2- exo-bispidines, such as 42, in the presence of a chemical signal. Thus these aza-cis-decalins and bispidines were synthesized and conformational properties such as energy barriers to interconversion and conformer ratios in several solvents, were determined rigorously using variable temperature and 2D-NMR experiments as well as calculated 13C chemical shifts
Metal complexation studies provided insight into the structural suitability of cis-decalins and bispidines as molecular switches. For the aza-cis-decalins such as 33, there is no dominant pathway for a binary-type conformational switch. Instead 1:1 and 2:1 metal:diamine complexes exist in equilibrium.*
Remarkably, 42 behaved as an unambiguous binary conformational switch; only 1:1 metal:diamine complexation occurred. Excess metal did not cause formation of 2:1 metal:diamine adduct, due to the steric hindrance from the bridging methylene group.*
Based on the results of the bispidines, a pyrene-functionalized bispidine 49 was prepared and developed into an allosteric cation sensor. Fluorescence studies of 49 titrated with alkaline and transition metal cations showed chelation-enhanced fluorescence emission.*
*Please refer to dissertation for diagrams
School code: 0175
Host Item Dissertation Abstracts International 64-10B
主題 Chemistry, Organic
Alt Author University of Pennsylvania
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