Estudio teórico de la reacción hetero diels - alder [4+2] entre los sistemas N-(orto, meta y para nitrofenil)maleimida y (E)-1-isopropenil-2-fenildiazeno
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Orozco García, Luis Felipe | 2015-01-13
The presence of two nitrogen atoms more electronegative than carbon,
combined with one or more substituent electro -atrayentes electron, origin in
azo-alkene, especially 1,2-Diaza-1,3-dienes, a pronounced character
electrophilic, and therefore their cycloadditions are predominantly inverse
electronic demand (Lemos, Cycloaddition reactions of conjugated azoalkenes
, 2010). However, the presence of neutral or more electron donating groups
instead of the electro-attractive azo-alkene groups, and reaction with strongly
electrodeficientes dienophiles, allow these dienes react via cycloaddition with
normal electronic demand. Therefore, the present study evaluated through
DFT methods, the mechanism for hetero Diels-Alder reaction with a normal
electronic demand, among N-(o, m and p-nitrophenyl) maleimide systems and
azo-alkene (E)-1-isopropenyl-2-phenyldiazene, B3LYP level theory / 6-311 +
G (d). The results indicate that gas phase approach endo form, produces
mechanisms kinetically favorable in all cases. Remarking a lower activation
energy for the endo approach between m-nitrophenyl) maleimide and azoalkene.
In all cases it is evident that such cycloadditions are exothermic. The
formation of the cycloadducts takes place through a concerted asynchronous
process, with the latest C-C bond formation (shorter link), compared to the
formation of the C-N bond. From the values of charge transfer (CT) and overall
electrophilicity difference (Δω), it follows that three cycloaddition may be
classified as Diels - Alder nonpolar.
LEER