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Chiral Discrimination in Rhodium(I) Catalysis by 2,5-Disubstituted 1,3 a,4,6 a -Tetrahydropenatalene Ligands -More Than Just a Twist of the Olefins?

Melcher, Michaela Christina LU ; Rolim Alves Da Silva, Bianca; Ivšić, Trpimir LU and Strand, Daniel LU (2018) In ACS Omega 3(3). p.3622-3630
Abstract

Chiral dienes are useful ligands in a number of asymmetric transition-metal-catalyzed reactions. Here, we evaluate the efficiency of 2,5-disubstituted 1,3a,4,6a-tetrahydropentalenes as ligands to rhodium(I). 2,5-Dibenzyl and diphenyl tetrahydropentalenes were synthesized in two steps and resolved, either chromatographically, or through fractional crystallization of diastereomeric rhodium(I) salts. When evaluated in a 1,4-arylation reaction, the 2,5-dibenzyl ligand gave up to 99% ee. The use of a well-defined rhodium complex as catalyst, Cs2CO3 as the base, and toluene/water as solvent was found to have a pronounced beneficial effect on the selectivity of the reaction. The homologous 2,5-diphenyl ligand on the other... (More)

Chiral dienes are useful ligands in a number of asymmetric transition-metal-catalyzed reactions. Here, we evaluate the efficiency of 2,5-disubstituted 1,3a,4,6a-tetrahydropentalenes as ligands to rhodium(I). 2,5-Dibenzyl and diphenyl tetrahydropentalenes were synthesized in two steps and resolved, either chromatographically, or through fractional crystallization of diastereomeric rhodium(I) salts. When evaluated in a 1,4-arylation reaction, the 2,5-dibenzyl ligand gave up to 99% ee. The use of a well-defined rhodium complex as catalyst, Cs2CO3 as the base, and toluene/water as solvent was found to have a pronounced beneficial effect on the selectivity of the reaction. The homologous 2,5-diphenyl ligand on the other hand proved to be highly prone to racemization/loss of chirality during catalysis. Control experiments reveal that this rearrangement proceeds via a rhodium-mediated 1,3-hydride shift. Implications for ligand design and catalysis are discussed.

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organization
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type
Contribution to journal
publication status
published
subject
in
ACS Omega
volume
3
issue
3
pages
9 pages
publisher
American Chemical Society (ACS)
external identifiers
  • scopus:85044836487
ISSN
2470-1343
DOI
10.1021/acsomega.8b00127
language
English
LU publication?
yes
id
fe0d0909-1d98-419b-be8a-4a1eda6bb33b
date added to LUP
2018-04-16 14:17:45
date last changed
2018-04-16 14:17:45
@article{fe0d0909-1d98-419b-be8a-4a1eda6bb33b,
  abstract     = {<p>Chiral dienes are useful ligands in a number of asymmetric transition-metal-catalyzed reactions. Here, we evaluate the efficiency of 2,5-disubstituted 1,3a,4,6a-tetrahydropentalenes as ligands to rhodium(I). 2,5-Dibenzyl and diphenyl tetrahydropentalenes were synthesized in two steps and resolved, either chromatographically, or through fractional crystallization of diastereomeric rhodium(I) salts. When evaluated in a 1,4-arylation reaction, the 2,5-dibenzyl ligand gave up to 99% ee. The use of a well-defined rhodium complex as catalyst, Cs<sub>2</sub>CO<sub>3</sub> as the base, and toluene/water as solvent was found to have a pronounced beneficial effect on the selectivity of the reaction. The homologous 2,5-diphenyl ligand on the other hand proved to be highly prone to racemization/loss of chirality during catalysis. Control experiments reveal that this rearrangement proceeds via a rhodium-mediated 1,3-hydride shift. Implications for ligand design and catalysis are discussed.</p>},
  author       = {Melcher, Michaela Christina and Rolim Alves Da Silva, Bianca and Ivšić, Trpimir and Strand, Daniel},
  issn         = {2470-1343},
  language     = {eng},
  month        = {01},
  number       = {3},
  pages        = {3622--3630},
  publisher    = {American Chemical Society (ACS)},
  series       = {ACS Omega},
  title        = {Chiral Discrimination in Rhodium(I) Catalysis by 2,5-Disubstituted 1,3 a,4,6 a -Tetrahydropenatalene Ligands -More Than Just a Twist of the Olefins?},
  url          = {http://dx.doi.org/10.1021/acsomega.8b00127},
  volume       = {3},
  year         = {2018},
}