Cycloaddition Reactions of an o-Quinoid 10-? Electron System, 2H-Pyrrolopyridine

Article abstract of DOI:10.1021/jo00319a030

The cycloaddition reactions of ethyl 2-methyl-2H-pyrrolo<3,4-c>pyridine-6-carboxylate (1) with electron-deficient dienophiles have been investigated.While the reaction with an equimolar amount of diethyl acetylenedicarboxylate gives the 1:1 adduct 7 at room temperature, the 1:2 adducts 8a and 8b are obtained in equal amounts with an excess of dienophile.The stereochemistry of these 1:2 adducts is described.The reaction with N-phenylmaleimide is either endo or exo selective, depending on the reaction conditions.The competitive formation of the endo and exo isomers at 40 deg C was measured by 1H NMR.The kinetics of the endo-exo conversion at 40 deg C indicate an external pathway for the isomerization.