Identification and Assignment of the Absolute Configuration of Biologically Active Methyl-Branched Ketones from Limnephilid Caddis Flies

2001 ◽  
Vol 2001 (16) ◽  
pp. 3175 ◽  
Author(s):  
Jan Bergmann ◽  
Christer Löfstedt ◽  
Vladimir D. Ivanov ◽  
Wittko Francke
Keyword(s):  
Absolute Configuration ◽  
Biologically Active ◽  
Caddis Flies ◽  
Active Methyl ◽  
The Absolute

Studies on Biologically Active Pteridines: III. The Absolute Configuration at the C-6 Chiral Center of Tetrahydrobiopterin Cofactor and Related Compounds1

1980 ◽  
Vol 87 (3) ◽  
pp. 951-957 ◽  
Author(s):  
Sadao MATSUURA ◽  
Takashi SUGIMOTO ◽  
Hiroyuki HASEGAWA ◽  
Shunsuke IMAIZUMI ◽  
Arata ICHIYAMA
Keyword(s):  
Absolute Configuration ◽  
Biologically Active ◽  
Chiral Center ◽  
The Absolute

Catalyst- and Silane- Controlled Enantioselective Hydrofunctionalization of Alkenes by Cobalt-Catalyzed Hydrogen Atom Transfer and Radical-Polar Crossover

2020 ◽  
Author(s):  
Kousuke Ebisawa ◽  
Kana Izumi ◽  
Yuka Ooka ◽  
Hiroaki Kato ◽  
Sayori Kanazawa ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Absolute Configuration ◽  
Kinetic Resolution ◽  
Hydrogen Atom Transfer ◽  
Biologically Active ◽  
Atom Transfer ◽  
High Concentration ◽  
Chain Reaction ◽  
Radical Chain ◽  
Radical Chain Reaction

Catalytic enantioselective synthesis of tetrahydrofurans, which are found in the structures of many biologically active natural products, via a transition-metal catalyzed-hydrogen atom transfer (TM-HAT) and radical-polar crossover (RPC) mechanism is described herein. Hydroalkoxylation of non-conjugated alkenes proceeded efficiently with excellent enantioselectivity (up to 94% ee) using a suitable chiral cobalt catalyst, <i>N</i>-fluoro-2,4,6-collidinium tetrafluoroborate, and diethylsilane. Surprisingly, absolute configuration of the product was highly dependent on the steric hindrance of the silane. Slow addition of the silane, the dioxygen effect in the solvent, thermal dependency, and DFT calculation results supported the unprecedented scenario of two competing selective mechanisms. For the less-hindered diethylsilane, a high concentration of diffused carbon-centered radicals invoked diastereoenrichment of an alkylcobalt(III) intermediate by a radical chain reaction, which eventually determined the absolute configuration of the product. On the other hand, a more hindered silane resulted in less opportunity for radical chain reaction, instead facilitating enantioselective kinetic resolution during the late-stage nucleophilic displacement of the alkylcobalt(IV) intermediate.

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