Iron-Catalyzed Oxidative Coupling of Benzylamines and Indoles: Novel Approach for Synthesis of Bis(indolyl)methanes

Abstract

A novel route for synthesis of bis(indolyl)methanes has been developed by the oxidative coupling of benzylamines and indoles in the presence of iron(II) triflate as a catalyst and molecular oxygen as an oxidant. This method promises versatility, cost-effectiveness, and efficiency.

Synthesis of (E)‐3‐Alkylideneindolin‐2‐ones by an Iron‐Catalyzed Aerobic Oxidative Condensation of Csp3–H Bonds of Oxindoles and Benzylamines

“…On the basis of above experimental results and earlier reports, [ 4a,12f ] a plausible mechanism is outlined in Scheme 6. Initially, the enol form of oxindole reacts with iron(II) bromide in the presence of oxygen to give an iron(III) enolate 12 .…”

Development of an imidazole salt catalytic system for the preparation of bis(indolyl)methanes and bis(naphthyl)methane

“…R f = 0.33 (40:10 PE:EA); mp 74–75 o C, lit. mp 71–72 o C [45]; 1 H NMR (400 MHz, CDCl 3 ) δ 0.80–0.90 (3H, m), 1.24–1.44 (8H, m), 2.20–2.38 (2H, m), 4.48 (1H, t, J = 6.0 Hz), 6.99 (2H, d, J = 2.2 Hz), 7.04 (2H, t, J = 7.5 Hz), 7.15 (2H, t, J = 7.6 Hz), 7.33 (2H, d, J = 8.0 Hz), 7.61 (2H, d, J = 7.9 Hz), 7.86 (2H, br s); 13 C NMR (100 MHz, CDCl 3 ) δ 22.7, 28.3, 29.5, 31.8, 31.9, 34.0, 111.0, 119.0, 119.7, 120.7, 121.4, 121.7, 127.7, 136.6; HRMS (ESI-) calcd for C 23 H 25 N 2 [M−H] − 329.1999, found 329.2012 (error 3.9 ppm). All spectroscopic data were in agreement with the literature values.…”

Oxidative Coupling of Benzylamines with Indoles in Aqueous Medium to Realize Bis‐(Indolyl)Methanes Using a Water‐Soluble Cobalt Catalyst and Air as the Oxidant

“…Unlike aldehydes and ketones, there are very few reports on catalytic methods for oxidative synthesis of BIM′s using alcohols and amines as substrates . In particular, Gopalaiah and co‐workers have reported iron catalyzed oxidative coupling of benzylamines and indoles, but the reaction has been carried out in chlorobenzene at 110 °C with higher catalyst loading …”

“…It further reacts with the indole molecule in the presence of Co(bpb) to form intermediate G followed by loss of benzylamine to give intermediate H . Intermediate H reacts with another molecule of indole to give the desired 3,3′‐benzylidenebis(1H‐indole) I . The formation of the intermediates E and F were confirmed by 1 H‐NMR and GC‐MS analysis of reaction mixture of 4‐methoxybenzylamine in the absence of indole (Schemes d, Scheme ).…”