Hg(OTf)2-catalyzed direct vinylation of tryptamines and versatile applications for tandem reactions

Abstract

Graphical AbstractWe have developed a unique catalytic protocol for direct gem-vinylation of tryptamine derivatives employing Hg(OTf) 2 as the optimum catalyst. The intermolecular vinylations with a series of aromatic acetylenes proceeded under ambient temperature at the C2 positions of indoles with high functional group tolerance. Based on the mechanistic insights, we further developed the tandem reactions successfully constructing a quaternary center.

Formation of a 1D-polymeric chain of Hg building blocks through C–C coupling under ambient conditions

“…The absence of any other impurities, therefore, suggests that Hg(II) is acting as a catalyst for the C-C coupling. 9 Moreover, the powder XRD spectrum of 1 is in agreement with the simulated PXRD patterns generated from single crystal data (Fig. S5 †).…”

Alkenylation of Arenes and Heteroarenes with Alkynes

“…Hg­(OTf) 2 (5 mol %) catalyzes the intermolecular alkenylation of tryptamines (3-substituted indoles) with alkynes (CH 2 Cl 2 , room temperature, 3 h), affording gem -2-vinyl-substituted tryptamines (79–86%) . The solid-supported Hg catalyst, viz., silaphenylmercuric triflate (10 mol %), was explored in the intramolecular cyclization of alkynes (CH 2 Cl 2 or MeCN, room temperature to 90 °C, 1–4 h) …”

“…Hg(OTf) 2 (5 mol %) catalyzes the intermolecular alkenylation of tryptamines (3-substituted indoles) with alkynes (CH 2 Cl 2 , room temperature, 3 h), affording gem-2-vinyl-substituted tryptamines (79−86%). 326 The solid-supported Hg catalyst, viz., silaphenylmercuric triflate (10 mol %), was explored in the intramolecular cyclization of alkynes (CH 2 Cl 2 or MeCN, room temperature to 90 °C, 1−4 h). 327 In conclusion, metals that catalyze (hetero)aryl alkenylation should be divided into two groups: the first group act as CC bond activators (e.g., indium, lanthanides and mercury), and the second group activates the C−H bond via formation of the C−M intermediate (e.g., manganese, rhenium, cobalt, and iridium).…”

Regioselective Direct C‐Alkenylation of Indoles

“…3‐Methylindole has been alkenylated with a couple of phenylacetylenes using Ru 3 (CO) 12 in the presence of NH 4 PF 6 as additive . A simple and mild procedure employs Hg II catalysis for the reaction of N ‐nosyltryptamine and N ‐nosyltryptophan with arylacetylenes (Scheme ) . The high toxicity of the catalyst is a severe limit for this method although it affords the target products in satisfactory yields and does not require any protection of the indole nitrogen atom.…”