Aza-Nazarov Synthesis of 2H-Pyrroles

Significance

Reported is the aza-Nazarov cyclization to form 2H-pyrroles. Since the 3-hy­droxypyrroles formed from the reaction proved too sensitive to be isolated, the reaction was conducted in the presence of acidic anhydrides to form the more stable esters. However, when the reaction was conducted in the presence of TFAA or pivaloyl chloride the free 3-hydroxypyrrole was isolated in poor yield in the tautomeric keto form. A reasonable mechanism supported by quantum chemical calculations is proposed and discussed at length. The design of indole as a leaving group is an innovative component of the reaction.