In situ vinylpyrrole synthesis. Diels‐Alder reactions with maleimides to give tetrahydroindoles

Abstract magnified image A series of 108 tetrahydroindoles has been prepared by a one‐pot synthesis from 2‐alkylpyrroles, cyclic ketones, maleimides, and an acid catalyst. A 5‐vinylpyrrole is formed by an acid‐catalyzed condensation of a 2‐alkyl‐substituted pyrrole with a ketone, which is subsequently trapped in situ by a maleimide in a predominantly endo‐addition Diels‐Alder reaction. Isomerization of the double bond into the pyrrole ring gives a tetrahydroindole with predominant cis‐fusion of the cycloalkane ring. J. Heterocyclic Chem., 46, 503 (2009).