Novel ligands for asymmetric reactions: Development of biconformational diamines as chemo-responsive molecular switches.

Format:

Book

Thesis/Dissertation

Author/Creator:

Phuan, Puay-Wah.

Contributor:

Kozlowski, Marisa C., 1967- advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Chemistry, Organic.

0490.

Penn dissertations--Chemistry.

Chemistry--Penn dissertations.

Local Subjects:

Penn dissertations--Chemistry.

Chemistry--Penn dissertations.

0490.

Physical Description:

299 pages

Contained In:

Dissertation Abstracts International 64-10B.

System Details:

Mode of access: World Wide Web.

text file

Summary:

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.

Notes:

Thesis (Ph.D. in Chemistry) -- University of Pennsylvania, 2003.

Source: Dissertation Abstracts International, Volume: 64-10, Section: B, page: 4948.

Supervisor: Marisa C. Kozlowski.

Local Notes:

School code: 0175.

ISBN:

9780496567539

Access Restriction:

Restricted for use by site license.