Copper-catalyzed tandem reaction of 2-alkynylanilines with benzoquinones: efficient access to 3-indolylquinones

Abstract

A simple, mild, catalytic and efficient method for the straightforward synthesis of an interesting class of 2-aryl/alkyl-substituted-3-indolyl quinones in good to high yields is reported for the first time. This atomefficient method proceeds via copper-catalyzed one-pot sequential intramolecular hydroamination (C-N bond formation) of 2-alkynylanilines followed by oxidative C-C coupling with benzoquinones.

An overview on the copper‐promoted synthesis of five‐membered heterocyclic systems

“…Unsymmetrical benzoquinones with methyl and methoxy substitutions tolerated this tandem reaction and gave a mixture of isomers with a 1:1 ratio. Very interestingly, unsymmetrical benzoquinone with phenyl substitution solely afforded one product in a regioselective manner (Scheme ) …”

Light induced cyclization of tryptamine-naphthoquinone hybrids

“…4 Their synthesis has been mainly based on the nucleophilic character of indole towards electrophiles to produce the characteristic indole(C-3)-quinone bond. In these methods Lewis acids 5,6 transition metal catalysis, 7 C-H activation, 8 activation "on water", 9 microwave irradiation 10 photo-induced addition to enones, 11 mechanochemical, 12 and oxidizing conditions have been employed. [13][14][15] In contrast, the formation of the isomeric C-2 Indole quinone compounds has been less studied.…”

A Commercially Available and User‐Friendly Catalyst for Hydroamination Reactions under Technical Conditions

“…Seminal work by Müller and co‐workers hinted the potential of even very simple salts of late transition metals as hydroamination catalysts, including [Cu(NCMe) 4 ](PF 6 ) , . Great advances have been achieved since in the intra‐ or intermolecular hydroaminations of alkynes and alkenes, although the catalytic systems reported are typically air‐sensitive/not readily available or use extremely toxic CuCN , . Hence, in a quest for a readily available copper(I) catalyst for hydroamination reactions, we decided to go back to tetrakis‐acetonitrile copper(I) derivatives and develop reactions as user‐friendly as possible by avoiding high purity solvents, and oxygen‐ or moisture‐free conditions.…”