scholarly journals Absolute configuration of seco‐eudesmanolide inuloxin D from experimental and predicted chiroptical studies of its 4‐ O ‐acetyl derivative

Chirality ◽  
2021 ◽  
Vol 33 (5) ◽  
pp. 233-241
Author(s):  
Jordan L. Johnson ◽  
Ernesto Santoro ◽  
Roukia Zatout ◽  
Ana G. Petrovic ◽  
Alessio Cimmino ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Acetyl Derivative

Alkaloids of Schelhammera pedunculata (Liliaceae). II. Reactions of schelhammeridine

1969 ◽  
Vol 22 (10) ◽  
pp. 2203 ◽  
Author(s):  
SR Johns ◽  
JA Lamberton ◽  
AA Sioumis ◽  
H Suares
Keyword(s):  
Acetic Acid ◽  
Hydrochloric Acid ◽  
Acetic Anhydride ◽  
Absolute Configuration ◽  
Acetic Acid Solution ◽  
Acetyl Derivative ◽  
Major Product ◽  
Ring System ◽  
Single Isomer ◽  
Formed Product

Catalytic hydrogenation of schelhammeridine (I) in acetic acid solution gives demethoxydihydroschelhammeridine (II), 1,2,6α,7- tetrahydroschelhammeridine (III), dihydroschelhammeridine (IV), and a tetrahydro derivative (V), the formation of which involves cleavage of the C5-N9 bond. The major product from heating schelhammeridine with 10% aqueous hydrochloric acid is the alcohol (VIIa) with the configuration at C 3 opposite to that in schelhammeridine. Other products are the alcohol (IX) and two amino alcohols (Xa) and (XIIa) which have a diphenyl ring system formed by the aromatization of ring A. The compounds (Xa) and (XIIa) have been shown to be diastereoisomers with the same absolute configuration for the dissymmetric diphenyl system, but the opposite configuration at C 7, and they have been characterized as N-acetyl derivatives (Xb) and (XIIb) which have been assigned the respective configurations shown in (XX) and (XVIII). On heating with acetic anhydride, schelhammeridine is converted into the N,O-diacetyl compound (XVa) which on hydrolysis affords (XVb), the optical antipode of (Xb). All three stereo-isomeric N-acetylamides (Xb), (XIIb), and (XVb), are oxidized to the same optically inactive ketone (XI). A mechanism for the acetic anhydride reaction that explains the formation of only a single isomer is discussed, and it has been shown that the formation of (XVa), enantiomeric with (Xc), in this reaction necessarily involves inversion of the configuration of the diphenyl system in the first-formed product, which must be the O-acetyl derivative of (XVIII). It is concluded that amide alcohols (XVIII) and (XX) retain the configuration for the diphenyl system that would be predicted from the known absolute configuration of schelhammeridine, but that the initially formed O-acetyl derivative of (XVIII) obtained in the reaction with acetic anhydride is converted quantitatively at the temperature of the reaction mixture into the O-acetyl derivative of (XXI) by inversion of the diphenyl configuration.

New rare atropisomers: structure elucidation, absolute configuration and antimicrobial activity

Planta Medica ◽  
2011 ◽  
Vol 77 (12) ◽  
Author(s):  
A Debbab ◽  
R Bara ◽  
A Pretsch ◽  
R Edrada Ebel ◽  
V Wray ◽  
...  
Keyword(s):  
Antimicrobial Activity ◽  
Absolute Configuration ◽  
Structure Elucidation

Influence of Absolute Configuration of Indanofan on Herbicidal Activity

2001 ◽  
Vol 26 (4) ◽  
pp. 383-384 ◽  
Author(s):  
Akemi HOSOKAWA ◽  
Osamu IKEDA ◽  
Chizuko SASAKI ◽  
Yasuko T. OSANO ◽  
Tetsuo JIKIHARA
Keyword(s):  
Absolute Configuration ◽  
Herbicidal Activity

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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