Rhodium‐Catalyzed Regioselective Ortho C−H Olefination of 2‐Arylindoles via NH‐Indole‐Directed C−H Bond Cleavage

Abstract

In the past decades, CÀH oxidative olefination of indole at C-2, C-3, C-4 and C-7 positions was well addressed. We report here a rhodium-catalyzed NH-indole-directed ortho CÀH bond olefination of 2arylindoles. This cross-dehydrogenative-coupling proved to be broad in substrate scope, tolerating a variety of functional groups. The synthesis of 6H-isoindolo[2,1-a]indoles via rhodium-catalyzed ortho CÀH olefination and subsequent intramolecular aza-Michael reaction of 2-arylindoles was also demonstrated.

Rhodium-Catalyzed Oxidative Annulation of 2- or 7-Arylindoles with Alkenes/Alkynes Using Molecular Oxygen as the Sole Oxidant Enabled by Quaternary Ammonium Salt

“…1 H NMR (400 MHz, CDCl 3 ) δ 8.22 (s, 1H), 7.68 (d, J = 7.6 Hz, 1H), 7.60–7.55 (m, 2H), 7.39–7.32 (m, 3H), 7.24–7.15 (m, 2H), 6.48 (dd, J = 2.0, 1.2 Hz, 1H), 6.33 (d, J = 16.0 Hz, 1H), 4.06 (t, J = 6.4 Hz, 2H), 2.23 (s, 3H), 1.59–1.51 (m, 2H), 1.31–1.25 (m, 2H), 0.86 (t, J = 7.2 Hz, 3H). 13 C NMR and HRMS data for the desired product were in agreement with the previously reported literature data [ 44 ].…”

“…1 H NMR (400 MHz, CDCl 3 ) δ 7.98 (s, 1H), 7.73–7.71 (m, 1H), 7.67 (d, J = 8.0 Hz, 1H), 7.42–7.36 (m, 2H), 7.32–7.25 (m, 4H), 7.24–7.18 (m, 4H), 7.03 (d, J = 8.4 Hz, 2H), 6.54 (dd, J = 2.0, 0.8 Hz, 1H), 2.26 (s, 3H). 13 C NMR and HRMS data for the desired product were in agreement with the previously reported literature data [ 44 ].…”

“…2-phenyl-1 H -indole is commercially available. The other 2-arylindoles were synthesized from phenylhydrazine hydrochlorides via Fisher indole synthesis [ 44 ]. 7-phenyl-1 H -indoles were synthesized from 7-bromo-1 H -indoles and phenylboronic acid via Suzuki coupling [ 34 , 35 ].…”

Recent development in transition metal-catalysed C–H olefination

“…Indole NH directed Rh-catalysed ortho -di-olefination of 2-arylindoles was presented by Huang and co-workers in 2018. 29 It is worth mentioning that when the reaction was performed in DMF instead of EtOAc, formation of 6 H -isoindolo[2,1- a ]indole took place through intramolecular aza-Michael reaction.…”

Revisiting the mechanism of the Fujiwara–Moritani reaction

“…[7][8][9][10] In recent years, directing scaffolds were also used very effectively in controlling selective olefination at distal positions. 11,12 Moreover, the reaction is no longer exclusive to Pd : Ru, [13][14][15][16][17][18] Rh [19][20][21][22][23] and Ir 24 complexes have also been reported to be effective catalysts for certain systems.…”