Substituent effects in 1,3-dipolar cycloadditions. Variable reaction paths for the cycloaddition of benzonitrile N-oxides to styrenes

1973 ◽  
pp. 1769 ◽  
Author(s):  
Alessandro Dondoni ◽  
Gaetano Barbaro
Keyword(s):  
Substituent Effects ◽  
Reaction Paths ◽  
Dipolar Cycloadditions

scholarly journals Additive-assisted regioselective 1,3-dipolar cycloaddition of azomethine ylides with benzylideneacetone

2014 ◽  
Vol 10 ◽  
pp. 352-360 ◽  
Author(s):  
Chuqin Peng ◽  
Jiwei Ren ◽  
Jun-An Xiao ◽  
Honggang Zhang ◽  
Hua Yang ◽  
...  
Keyword(s):  
Substituent Effects ◽  
Azomethine Ylides ◽  
Dipolar Cycloaddition ◽  
Dipolar Cycloadditions ◽  
Nitrobenzoic Acid

1,3-Dipolar cycloadditions of isatins, benzylamine and benzylideneacetones were studied to prepare a series of novel spiropyrrolidine-oxindoles – 4′-acetyl-3′,5′-diarylspiro[indoline-3,2′-pyrrolidin]-2-ones and 3′-acetyl-4′,5′-diarylspiro[indoline-3,2′-pyrrolidine]-2-ones in good yields of up to 94% and with good regioselectivities. Regioselectivities are reversible by the addition of water or 4-nitrobenzoic acid, respectively. The substituent effects on the regioselectivity were also investigated.

Elimination of Substituted Fluoren-9-ylmethyl Benzenesulfonates: Hammett Substituent Effects at a Mechanistic Borderline

1999 ◽  
Vol 64 (11) ◽  
pp. 1833-1848 ◽  
Author(s):  
Finbar G. Larkin ◽  
Rory A. More O'Ferrall ◽  
Donal G. Murphy
Keyword(s):  
Sodium Methoxide ◽  
Transition States ◽  
Substituent Effects ◽  
Small Extent ◽  
Bond Breaking ◽  
Reaction Paths ◽  
Independent Evidence ◽  
Leaving Group ◽  
Negative Hyperconjugation ◽  
Degree Of Similarity

Rates of elimination of fourteen substituted fluoren-9-ylmethyl benzenesulfonates have been measured in methanolic sodium methoxide and 90% aqueous ethanolic solutions of triethylamine, trimethylamine and 4-methyl morpholine. For the sodium methoxide, a linear Hammett plot with ρ = 0.74, consistent with reaction by an E2 mechanism, is observed. For the amine bases the Hammett plots are curved, suggesting a transition from an E2 mechanism for electron-withdrawing substituents to an irreversible E1cB mechanism with a smaller value of ρ for electron-donating substituents. The evidence for a change of mechanism is weakened by systematic and random deviations of substituents from correlations which span small changes in reactivity (less than ten-fold), by a surprisingly large value of ρ = 2 implied for the concerted (E2) reaction and by the possible influence of negative hyperconjugation. Nevertheless, it is consistent with independent evidence that the borderline between concerted and stepwise mechanisms is associated with chemically distinguishable reaction paths, even though pronounced carbanion character (and probably a small extent of bond-breaking to the leaving group) ensures a degree of similarity of structure and sensitivity to substituents of their transition states.

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