89771-80-2Relevant academic research and scientific papers
Azo Bridges from Azines, VII. - Diels-Alder Reactions with Inverse Electron Demand between Isopyrazoles and Cycloalkenes or Cycloalkadienes. - A Comparison of Acid Catalysis and Acceleration by Pressure
Beck, Karin,Huenig, Siegfried,Klaerner, Frank-Gerrit,Kraft, Petra,Artschwager-Perl, Uwe
, p. 2041 - 2052 (2007/10/02)
The acid-catalysed reaction of the isopyrazoles 1 and 2 with the cycloalkenes 3 - 8, norbornene (9), 1,4-cyclohexadiene (18), 1,5-cyclooctadiene (9), norbornadiene (20), and benzonorbornadiene (21) yields the expected azo-bridged ycyloadducts 10 - 17 nad 22 - 27.From 19 are also obtained the bisadducts 24a and 24b.At higher pressure (7 kbar) the non-acid -catalysed reaction of 2 and the previously mentioned olefines produces the respective cycloadducts usually in higher yields.In the case of 20 the additional bisadducts exo,exo-26b and endo,exo-26b are formed.Reaction rates for the (pressure-controlled) cycloadditions correlate with the reaction enthalpies of the cycloaddition between cycloalkenes and 1,3-cyclopentadiene.The exo/endo ratio of cycloadducts 25b, formed from 2 and 20 proves to be independent of temperature and pressure.
Azo Bridges from Azines, I. Isopyrazoles as Electron Deficient Dienes for the Synthesis of 2,3-Diazabicycloheptenes
Beck, Karin,Hoehn, Arthur,Huenig, Siegfried,Prokschy, Frank
, p. 517 - 533 (2007/10/02)
A general principle for + + 2> cycloaddition in Diels-Alder reactions with inverse electron demand is described, where protonated azines serve as electron deficient dienes and electron rich olefins as dienophiles.This reactivity pattern is illustrated by isopyrazoles 2a and 2b.The catalytic activity of some acids is studied and the reversibility of the cycloaddition is proved.Inter alia cycloadducts (endo-14a and endo-14b) are obtained with parallel C=C/N=N bonds, which show characteristic features in their UV and NMR spectra.
