A simple and efficient method for constructing azepino[4,5-b]indole derivatives via acid catalysis

Abstract

A new synthetic methodology has been developed to prepare the biologically important azepino[4,5-b]indole derivatives under Brønsted acid catalysis. The notable features of this protocol include its operational simplicity, high reaction yields and environmentally benign and mild reaction conditions.

Regioselective Synthesis of Indole-Fused Seven-Membered N-Heterocycles via Photoredox-Catalyzed Intramolecular Cyclization

“…1 H NMR (400 MHz, CDCl 3 ): δ 8.47 (s, 1H), 7.57 (d, J = 7.6 Hz, 1H), 7.18−6.97 (m, 4H), 6.94 (s, 1H), 6.93 (d, J = 7.6 Hz, 1H), 6.72 (s, 1H), 3.77 (s, 2H), 3.05 (t, J = 6.8 Hz, 2H), 2.96 (t, J = 6.8 Hz, 2H), 2.23 (s, 6H), 1.23 (br s, 1H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ): δ 136.8, 136. 5,136.3,128.1,127.2,126.8,122.0,121.6,118.9,118.6,113.3,111.1,50.0,47.6,25.6,19.4;HRMS (ESI) m/z: 279.1861; found, 279.1885.…”

Regioselective Direct C‐Alkenylation of Indoles

“…The second approach employs as substrates 2‐tryptamino ketones which by simple catalysis using trifluoromethanesulfonic acid afford azepinoindoles in good yield (Scheme ) . Better results are obtained with N ‐sulfonyl over N ‐benzylated derivatives and using arylketones which probably provide thermodynamically more stable azepinoindoles.…”

Synthesis of Tetrahydroazepines through Silyl Aza-Prins Cyclization Mediated by Iron(III) Salts

“…Classical methods to synthesize this type of heterocycles include Brønsted or Lewis acid-mediated cyclizations, 7 , 8 atom-transfer radical cyclization (ATRC), 9 cycloadditions, 10 , 11 conjugate addition cyclizations, 12 , 13 ring expansions (cyclopropanes, 14 aziridines, 15 azetidines, 16 − 18 2-cyano-6-oxazolopiperidine 19 ), and ring-closing metathesis. 20 − 25 Among the different types of acid-mediated cyclizations, the aza-Prins cyclization is a powerful tool for obtaining nitrogenated heterocycles.…”

“…Classical methods to synthesize this type of heterocycles include Brønsted or Lewis acid-mediated cyclizations, , atom-transfer radical cyclization (ATRC), cycloadditions, , conjugate addition cyclizations, , ring expansions (cyclopropanes, aziridines, azetidines, − 2-cyano-6-oxazolopiperidine), and ring-closing metathesis. − Among the different types of acid-mediated cyclizations, the aza-Prins cyclization is a powerful tool for obtaining nitrogenated heterocycles. It has been widely used for the synthesis of piperidines and pyrrolidines. − However, there are few examples of synthesis of tetrahydroazepines through this methodology. , In 2016, Barbero and co-workers achieved the synthesis of azepane rings, with an exocyclic double bond, through a diastereoselective silyl aza-Prins cyclization mediated by InCl 3 (Scheme ).…”