Regioselectivity of the SEAr-based cyclizations and SEAr-terminated annulations of 3,5-unsubstituted, 4-substituted indoles

• Published in: Beilstein journal of organic chemistry Vol. 18; no. 1; pp. 293 - 302
• Main Authors: Das, Jonali, Das, Sajal Kumar
• Format: Journal Article
• Language: English
• Published: Trakehner Str. 7-9, 60487 Frankfurt am Main, Germany Beilstein-Institut 08.03.2022
• Subjects: annulation; Chemistry; cyclization; fused indoles; regioselectivity; sear
• ISSN: 1860-5397; 1860-5397
• DOI: 10.3762/bjoc.18.33

Indole-3,4- and 4,5-fused carbo- and heterocycles are ubiquitous in bioactive natural products and pharmaceuticals, and hence, a variety of synthetic approaches toward such compounds have been developed. Among these, cyclization and annulation of 3,5-unsubstituted, 4-substituted indoles involving an electrophilic aromatic substitution (S E Ar) as the ring closure are particularly attractive, because they avoid the use of 3,4- or 4,5-difunctionalized indoles as starting materials. However, since 3,5-unsubstituted, 4-substituted indoles have two potential ring-closure sites (indole C3 and C5 positions), such reactions in principle can furnish either or both of the indole 3,4- and 4,5-fused ring systems. This Commentary will briefly highlight the issue by summarizing recent relevant literature reports.