scholarly journals The role of steric hindrance in the intramolecular oxidative aromatic coupling of pyrrolo[3,2-b]pyrroles

2016 ◽  
Vol 52 (77) ◽  
pp. 11539-11542 ◽  
Author(s):  
Maciej Krzeszewski ◽  
Paweł Świder ◽  
Łukasz Dobrzycki ◽  
Michał K. Cyrański ◽  
Witold Danikiewicz ◽  
...  
Keyword(s):  
Carbon Atom ◽  
Steric Hindrance ◽  
Sterically Hindered

Sterically hindered tetraaryl-pyrrolo[3,2-b]pyrroles undergo oxidative aromatic coupling, forming a fluorene scaffold linked via a spiro carbon atom with a novel π-conjugated scaffold.

Synthesis of Conjugated Triynes via Alkyne Metathesis

2019 ◽  
Author(s):  
Idriss Curbet ◽  
Sophie Colombel-Rouen ◽  
Romane Manguin ◽  
Anthony Clermont ◽  
Alexandre Quelhas ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
High Selectivity ◽  
Alkyne Metathesis ◽  
Cross Metathesis ◽  
Synthetic Strategy ◽  
Sterically Hindered ◽  
Site Selective

<div> <div> <div> <div> <p>The synthesis of conjugated triynes by molybdenum-catalyzed alkyne metathesis is reported. Strategic to the success of this approach is the utilization of sterically-hindered diynes that allowed for the site- selective alkyne metathesis to produce the desired con- jugated triyne products. The steric hindrance of alkyne moiety was found to be crucial in preventing the for- mation of diyne byproducts. This novel synthetic strategy was amenable to self- and cross-metathesis providing straightforward access to the corresponding symmetrical and dissymmetrical triynes with high selectivity. </p> </div> </div> </div> </div>

The effect of steric hindrance on the SRN1 reaction of some α-Alkyl-p-nitrobenzyl chlorides

1976 ◽  
Vol 29 (12) ◽  
pp. 2621 ◽  
Author(s):  
RK Norris ◽  
D Randles
Keyword(s):  
Oxygen Atom ◽  
Steric Hindrance ◽  
Lithium Salt ◽  
Dimethyl Sulphoxide ◽  
Sterically Hindered ◽  
Srn1 Reaction

The reactions of a series of α-substituted p-nitrobenzyl chlorides, p- NO2C6H4CH(Cl)R (R = Me, Et, Prt, But), with the lithium salt of 2- nitropropane in dimethyl sulphoxide and dimethylformamide have been studied. When R = Me or Et, competing SRN1 and SN2 processes take place, giving C- and O-alkylated products respectively. In the more sterically hindered cases where R = Pri or But, the only reaction taking place has been shown to be an SRN1 reaction with exclusive O-alkylation. These observations indicate that the SRN1 reaction is prone to steric hindrance, and that radical alkylation of the ambident nitronate ion occurs on the more accessible oxygen atom in sterically hindered situations.

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