Pd/C‐Catalyzed Cyclizative Cross‐Coupling of Two ortho‐Alkynylanilines under Aerobic Conditions: Synthesis of 2,3′‐Bisindoles

Abstract

A palladium-catalyzed cyclizative cross-coupling of two o-alkynylanilines to 2,3'-bisindoles under aerobic oxidative conditions was developed. Mechanistic studies suggested that the two catalytic cycles, namely the formation of 3-alkynylindoles 8 and their subsequent cyclization to bisindoles 5, are temporally separated. The aminopalladation of 3-alkynylindoles 8 occurred only after all the N,N-dialkyl-o-alkynylanilines were consumed. The solid support (activated charcoal) played a crucial role in the second intramolecular aminopalladation process.

Synthesis of Diversely Functionalized Oxindoles Enabled by Migratory Insertion of Isocyanide to a Transient σ‐Alkylpalladium(II) Complex

“…Depending on the reaction conditions,t he reaction can be tuned to generate either the amides 3 or esters 4. [25] In addition, athree-component reaction involving akey intermolecular direct arylation of an alkylimidoyl-Pd II complex was documented for the first time [26] and ac yclizative heterocoupling reaction [27] leading to the indolinone-benzoxazole framework was achieved using af unctionalized isocyanide (2b). An enantioselective domino carbopalladation/ isocyanide insertion/methoxylation has been developed.…”

Development of the Applications of Palladium on Charcoal in Organic Synthesis

“…An outstanding example of the synthesis of 2,3′‐bisindoles by Pd/C‐catalyzed cyclizative cross‐coupling of two o ‐alkynylanilines was reported in 2015 by Zhu et al [Eq. (69)] …”

“… the mechanism of the synthesis of 2,3′‐bisindoles. Redrawn with permission . Copyright 2015, Wiley‐VCH, Weinheim.…”

Asymmetric Cyclizative Dimerization of (ortho‐Alkynyl Phenyl) (Methoxymethyl) Sulfides with Palladium(II) Bisoxazoline Catalyst

“…Cyclizative dimerization of nucleophile‐bearing alkynes is a synthetically efficient transformation for the synthesis of bi‐heteroaryls, because the construction of two heteroaryls and the coupling reaction occur in a one‐step procedure . A few examples of cyclization–dimerization of alkynyl ketones, o ‐alkynylanilines,,,, o ‐alkynylphenols and homopropargylic amines have been reported, affording bifurans, bisindoles, bibenzofurans and bipyrroles in good to low yields in racemic form. If the cyclization–dimerization could be expanded to the synthesis of axially chiral biaryls, the process would be more valuable.…”