Pyrrole studies. Part 28. The effect of steric hindrance upon the reaction of 2-vinylpyrroles with dimethyl acetylenedicarboxylate

Steric interaction between the N-substituent and the vinyl substituent of 1-substituted 1-(1-substituted pyrrol-2-yl)ethenes destabilises the cisoid conformation (1b), thereby inhibiting (π4 +π2) cycloaddition reactions leading to dihydroindoles. Bulky N-substituents also sterically inhibit the Michael addition of dimethyl acetylenedicarboxylate at the 5-position of the pyrrole ring.