Acid‐Relayed Organocatalytic exo‐Diels–Alder Cycloaddition of Cyclic Enones with 2‐Vinyl‐1H‐indoles

Abstract With the aid of the hydrogen‐bond relay of ( S )‐camphorsulfonic acid, the enantioselective exo ‐Diels–Alder cycloaddition of cyclic enones and 2‐vinyl‐1 H ‐indoles catalyzed by prolinosulfonamide was developed. The corresponding Diels–Alder cycloadducts were readily obtained by a single recrystallization, free of column chromatography. Consequently, tetracyclic tetrahydrocarbazole ring systems with three contiguous stereogenic centers were prepared in moderate yields with excellent diastereoselectivities ( exo / endo up to >20:1) and enantioselectivities (up to > 99 % ee ).