Pericyclic reactions general considerations

Pericyclic reactions Continued) cycloadditions, 162-165 cycloreversions, 162-165 electrocyclic, 165 general considerations, 161 sigmatropic, 166-167... 

Competition Between Ene and Diels-Alder Reactions. One area of considerable research centers on the reactivity of diethyl azodicarboxylate with conjugated dienes, systems in which two pericyclic reaction pathways are possible Diels-Alder and ene. Although a number of researchers have investigated this area, no clear explanation for the preference of one pathway over another has emerged. In most cases, one reaction course seems to be strongly predominant. At this time, only generalizations are possible. 

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